Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org

 
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
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        Probing for Planets
                              Space agencies prepare
                                  next generation
                               of exoplanet hunters

T H E   U N I V E R S I T Y   O F   T E X A S   AT   A U S T I N   M c D O N A L D   O B S E R VAT O R Y
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
STARDATE STAFF                                                                                                                            MARCH/APRIL • Vol. 47, No. 2
            EXECUTIVE EDITOR
         Damond Benningfield
                 EDITOR
            Rebecca Johnson
             ART DIRECTOR

                                                                               F eatures                                           Departments
               C.J. Duncan
          TECHNICAL EDITOR
             Dr. Tom Barnes

                                                                      4 Poets, Philosophers, Queens, Astronomers
        CONTRIBUTING EDITOR
             Alan MacRobert                                                                                                           Merlin                                             3
        MARKETING MANAGER
              Casey Walker                                                       Early women astronomers drafted
        MARKETING ASSISTANT                                                      calendars, plotted eclipses, built                   Sky Calendar MARCH/APRIL                          10
              Joanne Duffy                                                       observatories, and helped shape
                                                                                 humanity’s early understanding of the                The Stars in MARCH/APRIL                          12
                                                                                 universe
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                                                                                                    On The Cover
University of Texas McDonald Observatory.                                                           Artist’s concept of Kepler-62f, the
                                                                                                    smallest planet the Kepler spacecraft
                                                                                                    has found orbiting in a star’s
                                               NASA AMES/JPL-CALTECH/T. PYLE

                                                                                                    habitable zone. Kepler’s mission
   Visit StarDate Online at
     stardate.org or on:                                                                            recently ended, but its successors
                                                                                                    will continue to probe exoplanets for
                                                                                                    their secrets. For more, see Page 16.

                                                                           This Page                                               Coming Up
                                                                           Hydrogen gas glows red in the Ghost Nebula,             Our May/June issue brings you excerpts from
                                                                                                                                                                                              NASA/ESA/STScI/H. ARAB (UNIV. OF STRASBOURG)

                                                                           seen by Hubble Space Telescope 550 light-               new books in astronomy and space science
                                                                           years away in the constellation Cassiopeia.             to spice up your summer reading. We’ll also
                                                                           The gas is heated by blasts of ultraviolet              bring you summer skywatching notes and
       S t a rD a t e                                                     radiation from the nearby blue giant star               charts, Merlin’s answers, and more.
       S t a rD a t e M a g a z i n e
       Frank N. Bash Visitors Center                                      Gamma Cassiopeiae (not shown), which is
                                                                           34,000 times more powerful than the Sun.

        2          MARCH/APRIL 2019
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
Merlin
Dear Merlin,                           tional force. Presumably they
   Celestial bodies (planets, as-      continue to draw in matter (and
teroids, comets, etc.) obey the        grow larger and gravitation-
laws of gravitational physics.         ally stronger) until all the
Is it possible to have a celestial     nearby matter is absorbed.
object that travels askew to the       Is it possible, then, that
gravitational forces of the solar      the galaxies we observe
system — something that plays          — billions of light-years
by rules that transcend our local      distant, and therefore bil-
forces?                                lions of years in the past
                     Bill Dockery      — have been consumed
             Knoxville, Tennessee      by a giant black hole and
                                       no longer even exist in

                                                                                                                                                                 ÖM
   Following the laws of phys-         our time frame?

                                                                                                                                                              STR
                                                                                                                                                             ND
ics isn’t just recommended, it’s                       Owen Daniel

                                                                                                                                                         LU
                                                                                                                                                        YN

                                                                                                                                                       E
required. There is no way for                             Fort Worth                                                                                  LA

any object to break those laws.
That’s a comforting thought,              Possible, but highly unlikely.
because otherwise scientists              Black holes in the centers
would have no way of knowing           of galaxies can grow to mon-
where any object was going, so         strous proportions. The larg-       give birth to new stars.)            Kuiper Belt, which is a dough-
they might never know if an            est yet measured top 10 bil-           Also, keep in mind that while     nut-shaped region beyond the
object endangered Earth.               lion times the mass of the Sun,     10 billion solar masses is a lot,    realm of the major planets.
   Having said that, Merlin will       which certainly produces a          it’s insignificant compared to       The calculations aren’t precise
add that the motions of objects        powerful gravitational pull.        the mass of a major galaxy.          enough to pinpoint the possible
in the solar system can be af-            Yet several things conspire      The Milky Way, for example,          planet’s location, though, so
fected by objects outside the          to prevent a black hole from        has a mass of more than a tril-      astronomers must scan large
solar system. A passing star, for      devouring its entire host gal-      lion Suns, and its disk spans        regions of the sky — far from
example, can stir up the Oort          axy. For one thing, as a black      100,000 light-years or more.         the ecliptic — to try to find it.
Cloud, which is a vast shell of        hole “feeds,” it surrounds itself   All of that material exerts its         Even though the planet is
comet-like bodies that extends a       with a spinning disk of gas. As     own gravitational pull, keep-        estimated to be several times
light-year or more from the Sun.       the gas gets closer to the black    ing stars and gas clouds from        Earth’s diameter, it is hun-
These objects can get enough of        hole it moves faster, so it pro-    falling toward the central           dreds of times farther from the
a push to fall toward the Sun,         duces friction. That heats the      black hole.                          Sun than Earth is, so sunlight
where they could possibly run          gas to millions of degrees, so it      So while astronomers can’t        would be only a tiny fraction
into Earth or another body.            produces a lot of radiation. The    be sure that black holes haven’t     as strong as at Earth. It the
   Such encounters strictly fol-       radiation produces pressure         sucked up their entire galactic      planet is at its farthest pro-
low the laws of physics, how-          that pushes away the material       homes, they know that it’s not       jected distance, in fact, sun-
ever — no cheating allowed!            that’s trying to fall toward the    likely.                              light would be less than one-
                                       black hole. That acts as a tidy                                          millionth as strong as at Earth,
Dear Merlin,                           regulator, preventing the black     Dear Merlin,                         which means there would be
   As I understand black holes,        hole from overindulging. (The          Why is Planet 9 so difficult      little to illuminate it. Objects
they tend to exist in the centers of   outward-moving pressure also        to track down, especially if it is   in that part of the solar sys-
galaxies, and that nothing (even       can cause clouds of gas around      as large as presumed? Is it too      tem typically are darkened by
light) can escape their gravita-       the black hole to collapse and      far away from the Sun? Would it      long exposure to cosmic radia-
                                                                           be found on the ecliptic with the    tion, too, so a possible Planet 9
                                                                           other planets?                       would be quite dark.
                                       Send questions to                                        Corrin Gani        The planet might shine
                                       Merlin
                                                                                                     Austin     brighter in the infrared, but
                                       StarDate
  Merlin is unable to send             University of Texas at Austin
                                                                                                                still would be a faint target. So,
  personal replies. Answers to         2515 Speedway, Stop C1402             Astronomers have inferred          as with the discovery of Pluto
  many astronomy questions are         Austin, TX 78712                    the presence of Planet 9 from        almost a century ago, if Planet
  available through our web site:      stardatemerlin@gmail.com            the alignment and motions of         9 exists it will take a lot of pa-
  stardate.org/astro-guide             stardate.org/magazine               a group of iceballs outside the      tient searching to find it.

                                                                                                                                    S ta r D at e 3
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
POETS,
PHILOSOPHERS,
QUEENS,
ASTRONOMERS
Early women astronomers drafted calendars, plotted
eclipses, built observatories, and helped shape
humanity’s early understanding of the universe

By Jasmin Fox-Skelly

4   MARCH/APRIL 2019
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
Visitors check out Cheomseongdae,
the observatory created by Sonduk.
Opposite page, from left: Sonduk; a
        modern depiction of Hypatia

                                       TOP6BIN/WIKIPEDIA; LEFT PAGE, FROM LEFT: WIKIMEDIA, NASA/CXRO/CFA

                     S ta r D at e 5
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
H
                                enrietta Swan Leavitt helped make the expanding universe possible. She discovered that
                                a class of bright pulsating stars made perfect “standard candles” for determining the scale
                                of the universe: Measure such a star’s maximum brightness and the length of its pulses
                                and you could determine its distance. Edwin Hubble used those stars to discover that
                 swirling, spiral-shaped motes of matter are far outside the Milky Way galaxy, greatly increasing the size
                 of the known universe. He also used them as a first step in determining that the universe is expanding.
                   Leavitt’s discovery helped revolutionize humanity’s concept of the universe. She wasn’t the first
                 woman to do so, however. History is full of examples of female astronomers whose work changed the
                 way we think about the cosmos. In fact, some of the very first astronomers were female, and women
                 have been studying the stars since antiquity. From the ancient Greeks, Romans, Egyptians, and Sume-
                 rians, here are the stories of some of the earliest women astronomers.

                 EN HEDU’ANNA                              throughout the year, allowing her to       ing the Moon, which means building
                 En Hedu’anna was a princess who           create a lunar calendar. She also likely   a table that plotted the phase and
                 was born about 4,300 years ago in         recorded the seasons and the position      position of the Moon at various times
                 Sumer, part of the historical region of   of the Sun.                                of day throughout the month. It could
                 southern Mesopotamia, which is part         “The term ‘scientist’ did not come       then be used to forecast crop planting
                 of modern-day Iraq. Her father, King      into general use until the mid-19th        and harvesting dates.”
                 Sargon of Akkad, united the cities of     century,” says Sethanne Howard, an           According to Howard, it is from the
                 northern and southern Mesopotamia         astronomer and author of the book The      work of these early astronomers that
                 and established a mighty empire. To       Hidden Giants, which tells the story of    modern religious calendars developed.
                 help consolidate his power he ap-         more than 4,000 years of women in          For example, we date Easter, Passover,
                 pointed his daughter as head priestess    science, technology, engineering, and      and Ramadan using work derived by
                 of the temple of the Moon goddess in      mathematics. “Instead, scientists were     the ancient Sumerians.
                 the city of Ur.                           known as astronomers/mathemati-              En Hedu’anna is perhaps most fa-
                   En Hedu’anna’s job involved de-         cians, philosophers, or priestesses.       mous as the first known poet in histo-
                 ciding when crops should be planted         “En Hedu’anna controlled the ex-         ry, earning her the title of the “Shake-
                 and harvested and when important          tensive agricultural enterprise sur-       speare of Sumeria.” Like other Sumeri-
                 religious festivals should take place.    rounding the temple as well as reli-       an writings, her poems were imprinted
                 To do this, she observed the Moon         gious activities scheduled around the      on damp clay tablets, which were left
                 and tracked its position across the sky   year. Her calendar was based on track-     to harden in the sunlight. Many of

                 An ancient
                 Sumerian disk
                 depicts En
                 Hedu’anna (third
                 figure from right).
     IA
IPED        IK
      KIR/W
   ZUN

                 6        MARCH/APRIL 2019
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
these still survive, including three long                                   Pythagoras teaches a class of women, perhaps including
poems to the goddess Inanna, three                                                Theano (foreground, facing away from Pythagoras
poems to the god Nanna, and 42 tem-
ple hymns that can be found in trans-
lation today. The most famous tablet,
honoring Inanna, is at the University
Museum in Philadelphia.
  Many of her writings allude to her
work studying the Moon and stars. For
example, in one hymn she writes:
    In the gipar the priestesses’ rooms
    that princely shrine of cosmic order
    they track the passage of the moon.
Another reads:
    The true woman who possesses
      exceeding wisdom,

                                                                                                                                     WIKIPEDIA
    She consults a tablet of lapis lazuli
    She gives advice to all lands…
    She measures off the heavens,           She wrote books entitled Cosmology,        Bicknell, a classical scholar at Monash
    She places the measuring-cords on       The Theorem of the Golden Mean, The        University in Victoria, Australia, the-
      the earth.                            Theory of Numbers, and The Construc-       orized that Aglaonice’s disappearing
  “This poem describes the work of a        tion of the Universe. She also wrote a     Moons could have occurred during
scientist and leader,” says Howard. “To     biography about her husband, Life of       a solar cycle that is different from its
measure off the heavens is to engage        Pythagoras.                                well-known 11-year cycle of increas-
in astronomy, whilst to measure the            Theano theorized that the universe      ing and decreasing magnetic activity.
Earth requires surveying skills as well     consists of 10 concentric spheres,           Whatever the case, Aglaonice is
as astronomy. These are all technical       which held the Sun, Moon, Saturn,          written about in a number of ancient
subjects requiring great skill to ac-       Jupiter, Mars, Venus, Mercury, Earth,      Greek texts. In the book Instructions
complish.”                                  an unseen counter-Earth, and the stars.    for Married Couples, written around
  En Hedu’anna was the first in a long                                                 the end of the first century AD, Plu-
line of Sumerian astronomer-priest-         AGLAONICE                                  tarch, a renowned biographer and es-
esses, of whom little is known. Her         Around the time that Greek astrono-        sayist, writes:
achievements are especially remark-         mers first used geometry to predict          “Aglaonice the daughter of Hegetor
able considering that she lived and         that Earth was round, Aglaonice, the
worked 2,000 years before the Golden        daughter of Hegetor (or Hegemon) of
Age of Greece and just 900 years after      Thessaly, was using her observations
writing had been invented.                  of the phases of the Moon to master
                                            the art of predicting lunar eclipses.
THEANO                                      In fact, not only did she predict the
To find the next female astronomer          times of lunar eclipses, she also calcu-
of whom anything is known, fast for-        lated their degree of brightness. She
ward to circa 546 BC and the ancient        was said to be able to predict when
Greeks. One of the scientific leaders of    an eclipsed Moon would completely
the era was Pythagoras, a philosopher       disappear — a trick she used to her
who founded a movement of political         advantage when convincing people
and religious teachings and calculat-       that she could command the Moon.
ed the numerical constant pi, which,          Total “blackouts” of the Moon, in
among other things, can be used to          which the eclipsed lunar disk turns
calculate the area of a circle. However,    completely black instead of orange or
few know that his wife, Theano, also        red, are almost unheard of, and have
was an accomplished astronomer and          sometimes been attributed to volca-
mathematician. After her husband’s          nic dust spewing from an eruption.
death she supposedly led his followers,     However, historical records show that
the Pythagoreans.                           there were no such eruptions during
  Theano reportedly wrote many texts        Aglaonice’s time, making it a mystery
                                                                                                                                     ALZINOUS/WIKIMEDIA

on medicine, physics, mathematics,          as to how the sky became so dark that
                                                                                                             A modern-day artist’s
and psychology, and was especially          people believed the Moon had disap-
                                                                                                           impression of Aglaonice
interested in issues related to children.   peared. In a paper in the 1980s, Peter

                                                                                                                       S ta r D at e 7
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
being thoroughly conversant with the       cal treatise considered by some to be             actions prudent and public-spirited,
periods of the Full Moon when it is        the most influential textbook ever                and the rest of the city gave her suit-
subject to eclipse, and knowing be-        written, and Book III of Ptolemy’s                able welcome and accorded her special
forehand when the moon was due to          Almagest, which described the move-               respect.”
be overtaken by the Earth’s shadow,        ments of the stars and planets and sug-              One man with whom she developed
imposed upon audiences of women            gested that the Sun revolves around               a particularly close friendship was the
and made them all believe that she         Earth — a model of the universe that              governor of Alexandria, Orestes. Un-
drew down the Moon.”                       wouldn’t be overturned until the time             fortunately for Hypatia, though, her
  In fact, Aglaonice was so famous         of Copernicus and Galileo.                        association with him would lead to her
in her time that she was the subject         Hypatia also taught students, includ-           gruesome death.
of an ancient Greek proverb, “as the       ing a man named Synesius. Much of                    Hypatia lived in an era of extreme
Moon obeys Aglaonice.” It’s likely         what we know about her comes from                 religious and sectarian conflict. The
that she was seen as a sorceress, and      letters between the two. These letters            archbishop of Alexandria, Cyril, was
later authors referred to her and other    include instructions on how to con-               particularly intolerant of other faiths.
female astronomers of the period as        struct an astrolabe — a sort of portable             A power struggle broke out between
the “witches” and “enchantresses” of       astronomical calculator that can keep             Cyril and Orestes, with Hypatia caught
Thessaly.                                  track of the Sun, Moon, and stars.                in the middle. The conflict between
                                             Hypatia never married, although the             them peaked after Cyril led a mob
HYPATIA                                    Suda Lexicon, a Byzantine 10th-centu-             that expelled the Jews from the city
Perhaps the most famous female as-         ry encyclopedia of the Mediterranean              and ransacked their homes and tem-
tronomer of ancient times was Hypa-        world, describes her as being “exceed-            ples, which followed the massacre of a
tia, who was born in Alexandria,           ingly beautiful and fair of form ... in           group of Christians by Jewish extrem-
Egypt, which at the time was con-          speech articulate and logical, in her             ists. Orestes complained to the Roman
trolled by Rome. Although still a cen-
ter of culture and learning, by the time
Hypatia was born, sometime between
the years 350 and 370, the city was
in decline. Its famous library, home to
half a million scrolls, had been burned
down (although it was rebuilt). By
364, the great Roman Empire had split
in half, and fighting had broken out
between Alexandria’s Christians, Jews,
and pagans.
   Hypatia was the daughter of Theon,
the last known member of Alexan-
dria’s university (which was associated
with the library) and a mathematician
and astronomer. Hypatia continued
her father’s work and taught philoso-
phy, math, and astronomy. Her lec-
tures were well attended, and people
traveled from great distances to hear
her talk.
   The philosopher Damascius wrote
after her death: “Donning [the robe
of a scholar], the lady made appear-
ances around the center of the city,
expounding in public to those willing
to listen on Plato or Aristotle.”
   Hypatia was one of the last great
thinkers of ancient Alexandria, and
wrote commentaries on such famous
classical works as Diophantus’ Ar-
ithmetica, an ancient Greek text on          An illustration of the 1893 play ‘Hypatia,’ based on an 1853
mathematics and algebra. Other texts         novel. Hypatia’s life has been depicted in many books,
                                                                                                                                        WIKIPEDIA

that she wrote commentaries about in-        plays, and movies, including the 2009 film Agora.
clude Euclid’s Elements, a mathemati-

8       MARCH/APRIL 2019
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
government in Constantinople, which
led to a rift between the two men.
When Orestes refused Cyril’s attempts
at reconciliation, Cyril’s monks tried
unsuccessfully to kill him.
  Unfortunately for Hypatia, a rumor
spread that she was preventing Or-
estes and Cyril from reconciling. As a
pagan who publicly spoke about non-
Christian ideas, she was an easy target,
and in the year 415 or 416, a mob of
Christian fanatics led by Peter the
Lector dragged her from her carriage
into a church, where they stripped her,
beat her to death, tore her body apart,                                                       Resources
and burned it.
                                            Queen                                             Books
  Alexandria’s university and library
were burned not long afterward, end-        Sonduk                                            The Unforgotten Sisters: Female Astronomers and Scientists
ing the city’s long reign as one of the                                                       before Caroline Herschel, by Gabriella Bernardi, 2016
world’s leading centers of learning and                                                       The Hidden Giants: 2nd Edition, by Sethanne Howard,
science.                                                                                      2013

                                                                                  WIKIMEDIA
                                                                                              Hypatia of Alexandria: Mathematician and Martyr, by
QUEEN SONDUK                                                                                  Michael A.B. Deakin, 2007
The final female astronomer on our         wrote: “Will we ever know the truth
list is Queen Sonduk, the first female     about the stars? I am too young to ven-            Hypatia: Her Life and Times, by Faith L. Justice, 2013
ruler of the Korean Buddhist kingdom       ture a theory about our universe. I only           Hypatia: The Life and Legend of an Ancient Philosopher,
known as Shilla, who ascended to the       know that I want to understand more                by Edward J. Watts, 2017
throne in 632. She had developed a         deeply. I want to know all I can know.
keen interest in the stars as a child,     Why should it be forbidden?”
but was prevented from studying as-          After she became queen, Sonduk                   Internet
tronomy because women were seen as         created Cheomseongdae (“tower of                   Women Astronomers Through History
subordinate to men, and education for      the stars”), an observatory that was               adsabs.harvard.edu/full/2008POBeo..85..207D
girls was considered improper. When        built according to her design. The                 Theano
she was 15, it is rumored that Sonduk      milk bottle-shaped tower, which is                 www.agnesscott.edu/lriddle/women/theano.htm
asked the Chinese ambassador, Lin          about 30 feet tall, was constructed
                                                                                              Hypatia of Alexandria
Fang, who was also an astronomer, to       from 365 stones, one for each day of
                                                                                              http://www-history.mcs.st-andrews.ac.uk/Biographies/
teach her more about the universe. He      the year. Observations of the Sun and
                                                                                              Hypatia.html
reportedly replied, “Surely you cannot     Moon probably helped determine the
imagine that I would converse on such      planting and harvesting seasons, while             Hypatia, Ancient Alexandria’s Great Female Scholar
a serious subject with a young lady? It    observations of the stars, which were              www.smithsonianmag.com/history/hypatia-ancient-alexan-
would be unnatural and wholly against      important to astrology, would have                 drias-great-female-scholar-10942888
the laws of propriety.”                    had important political significance.              Hypatia of Alexandria: The Passing of Philosophy to
   The relationship between Sonduk         The observatory is still standing — the            Religion
and Lin Fang deteriorated further          oldest surviving astronomical observa-             www.ancient.eu/article/76/hypatia-of-alexandria-the-passing-
when Lin Fang convinced the king to        tory in East Asia.                                 of-philosophy-to
introduce a new official calendar based                                                       The Unforgotten Sisters: Sonduk, the astronomer queen
on the Chinese Sui calendar. After           These five examples show that                    cosmosmagazine.com/space/the-unforgotten-sisters-sonduk-
Sonduk correctly predicted when a          despite facing incredible obstacles,               the-astronomer-queen
solar eclipse was to occur, an event       women have shared the exciting world
                                                                                              Queen Seondeok
missed by the official calendar, the am-   of science with men from the be-
                                                                                              www.ancient.eu/Queen_Seondeok
bassador became angry and reportedly       ginnings of written history, making
said, “Astronomy is not for women.         important contributions to human-                  UNESCO: Cheomseongdae Observatory
Go do something female like look           ity’s ever-increasing knowledge of the             www3.astronomicalheritage.net/index.php/show-entity?identi
after silkworms.”                          universe.                                          ty=19&idsubentity=1
   The king consequently forbade Son-
duk to study astronomy. At the age         Jasmin Fox-Skelly is a science writer in
of 15, in a message she placed in her      Cardiff, Wales, and a previous contribu-
grandmother’s ancestral jar, Sonduk        tor to StarDate.

                                                                                                                                        S ta r D at e 9
Probing for Planets Space agencies prepare next generation of exoplanet hunters - Stardate.org
by Alan MacRobert

S   pring has sprung, and its stars are making their
    move into prominence. Regulus, Leo’s bright
heart, is moving high across the south. Spica, shining
                                                                    the height of the planet’s os-
                                                                    tentatious display last sum-
                                                                    mer, it was three times bright-
                                                                                                        MARCH 16 - 31
                                                                                                        Sirius, brightest spark of
                                                                                                     the evening sky, now shines
                                                                    er than Sirius!                  due south as the stars begin
in Virgo, rises high by March’s end. In April, look for               Look to the upper right        to come out. How early can
the Moon and Mars to stage appearances alongside                    of Sirius for Orion. Procyon     you spot Sirius in the fading
Taurus, the bull, and its bright eye Aldebaran.                     shines to Sirius’ upper left. Be-light of day? Face south. To
                                                                    telgeuse, Orion’s Mars-colored   tell how high to look, subtract
                                                                    shoulder, teams up with Sirius   your latitude from 73 degrees.
MARCH 1 - 15                       the seasonal westward turn-      and Procyon to form the Win-     For example, Austin is at lati-
   Is a planet ever unwelcome? ing of the constellations as         ter Triangle, showy and equi-    tude 30 degrees. So at Austin
When Mars is in the evening Earth goes around the Sun.              lateral.                         you’ll find Sirius 43 degrees
sky, it’s always that guest who      But by now we’ve far out-        Leo stands high in the east    above horizontal when it’s
just stays and stays. And, like run Mars and left it in the         to southeast, with Regulus as    due south.
the inebriated life of the party distance, small and faint. So      his modestly bright forefoot.       And how high is that? For
who never gets the message, in early March, as we see it            Leo’s Sickle asterism extends    most people, your fist at arm’s
Mars just keeps turning dim- crossing Aries, it’s a paltry          to the upper left from Regulus.  length is about 10 degrees tall.
mer and less interesting.          magnitude +1.2 (paltry for a       And since it’s now almost      That’s a good enough mea-
   Last summer, the Red Plan- naked-eye planet). And in a           spring, the Big Dipper stands    suring tool to get you close.
et was the night-life dazzler, telescope it looks like a tiny,      on its handle high in the           Sirius is the brightest star
attracting everyone’s atten- disappointing little blob.             northeast as soon as the stars   of Canis Major, the big dog.
tion with its closest,                                                                                          More of the con-
brightest opposition                                                                                            stellation comes
in 15 years. Those                                                                    March 26                  into view as night
days are gone, but                                                  March 27                                    arrives. Look for
Mars isn’t. It re-                                                                                              Murzim 5 degrees
mains high in the                         Saturn                             Jupiter                            to Sirius’ right.
west in early eve-                                                                           Antares            Its name means
ning, a mediocre                                       March 28                                                 “The Announcer;”
remnant of its for-                March 29                                                                     Murzim always pre-
mer self.                                                                                                       cedes Sirius across
   Why does Mars al-                                                                                            the sky, like a herald
ways do this? The sit-                                                                                          clearing the way for
uation is not caused                                                                                            the king.
by Mars itself, but                                                                                                Look about 10
by our viewing plat-                                                                                            degrees below Siri-
form from the mov-                                                                                              us, and a bit to the
ing Earth. We’re the                                                                                            left, for the triangle
next planet closer to                                                                                           of the dog’s hind-
                                                                                                             CJ DUNCAN

the Sun, and not by         30 minutes before sunrise                             S                             quarters and tail-
very much as solar-                                                                                             tip. These four stars
system distances go. So, after       Spot it in the west after      come out.                        plus Sirius form a big-bladed
opposition, Mars moves along dark. It’s the brightest point            For early risers, three plan- meat cleaver with a short
its orbit only a little slower below the Pleiades. As always,       ets await in early dawn. Ju- handle at the bottom; Sirius is
than Earth does on its. This its fire-orange color helps to         piter dominates the south as a sparkle on the cleaver’s top
means that compared to the give it away. The waxing cres-           morning twilight begins, with back corner.
other outer planets, Mars cent Moon hangs under it on               Antares and the head of Scor-       With the arrival of deep
takes a long time to fall behind the evening of March 10 and        pius to its right. Look two or night in an un-light-pollut-
us in its orbit.                   to the left of it on the 11th.   three fists to Jupiter’s lower ed sky, the full stick figure of
   Here’s another way to view        Sirius shines much brighter    left for Saturn, dimmer and Canis Major comes into view.
the situation. Mars’ fast mo- in early evening in the south.        yellowish. Follow this line far- He’s seen in profile, prancing
tion eastward against the eve- The star sparkles white with         ther to the lower left and you on his hind feet. Sirius is a
ning constellations, from our 12 times as much light (at            hit bright Venus, lower every shiny dog tag on his chest,
viewpoint, partly counteracts magnitude –1.5) as Mars. At           morning.                         Murzim is his forefoot, and

10       MARCH/APRIL 2019
the last several weeks. By April    is perhaps the most famous             down when you face north.
 Meteor Watch                                1, the Pleiades is passing a cou-   double star for amateur tele-            Look below the Big Dipper
                                             ple of finger widths to Mars’       scopes, though its compo-              for the much dimmer Little
  The Shower
                                             right. The cluster moves down       nents are a less interesting           Dipper. It’s highlighted only
  Lyrids
                                             to the lower right thereafter.      icy white.                             by Polaris, its handle-end on
  Peak                                          Look to the left of Mars for                                            the left, and the two stars
  Night of April 22                          Aldebaran, slightly brighter.       APRIL 16 - 30                          forming the end of its bowl
                                             On the evening of April 8, the        The Arch of Spring is form-          on the right: Kochab and
  Notes                                      waxing crescent Moon hangs          ing up nicely high in the west.        Pherkad, the “Guardians of
  The Lyrids are modest, with around         under the arc of Mars, Al-          Pollux and Castor, nearly hor-         the Pole,” forever circling Po-
  one or two dozen meteors per hour          debaran, and the Pleiades. On       izontal, form its top. The south       laris.
  at best. The Moon climbs into view         the 9th, the Moon poses above       end of the Arch is Procyon, to           If you have an open hori-
  before midnight and is about 90            Aldebaran.                          their lower left. The other end,       zon to the north, look low on
  percent full, so it will wash out most        With the coming of April,        farther flung to their right,          the other side of Polaris from
  of the meteors.                            Arcturus, “the spring star,”        consists of Menkalinan (Beta           the Big Dipper for the dipper’s
                                             twinkles in the east. Spica,        Aurigae) and Capella.                  eternal opposite: W-shaped
his faint, pointy-nosed head                 not quite as bright, is well off      The Arch of Spring is the            Cassiopeia, lying low for the
is a long triangle to Sirius’                to its right or lower right. If     last, trailing half of the even        warm season.
left and upper left. The stick               you live as far south as Miami,     bigger Winter Hexagon.                   Turn around. Look high
figure becomes obvious once                  you’ll find Arcturus and Spica      But not all the other Hexa-            overhead in the south for
you know it.                                 equally high. Farther north of      gon stars are yet gone. Sirius         Leo. We see the lion in profile,
   Now that winter is turning                there your eastern horizon is       sparkles brightly, low in the          stalking westward, with its
to spring, Orion tips south-                 tilted differently with respect     southwest, for a while dur-            tail-star Denebola on the left
westward, to the right of Sir-               to the stars, so Arcturus ap-       ing and after twilight. From           and the Sickle pattern form-
ius as soon as night is fully                pears higher.                       there, look to the right for           ing the lion’s head, mane, and
dark — and Orion’s Belt is in                   High to the upper left of        Orion with his horizontal belt.        forequarters on the right.
its horizontal springtime ori-               Arcturus, in the northeast,         Can you still spot Rigel down            Leo always announces
entation. The belt points to                 the Big Dipper is starting          under the belt? Continuing to          spring. Now that spring is
the left, back to Sirius, and                to turn over to dump April
a little farther to the right,               showers. The dipper’s curv-
toward Aldebaran in Taurus.                  ing handle arcs back toward            Springing a New Season
   Look to the lower right of                Arcturus.
                                                                                    Spring begins in the northern hemisphere at 4:58 p.m. CDT March
Aldebaran for Aldebaran-                        The dipper handle can also
colored Mars. How closely,                   guide you to a lesser-known
                                                                                    20 as the Sun crosses the equator heading north. For many of us in
to your eyes, do their colors                sight. If you picture the han-         modern times, that moment, the spring equinox, is little more than a
match? To me, the tint of                    dle and the side of the dipper         notation on the calendar. But to many cultures in bygone centuries, it
Mars looks just a trace deeper               bowl that it’s attached to as          was a time for celebration, as the Sun warmed the earth and banished
orange.                                      a segment of a (very rough)            the long, cold nights of winter.
                                             circle, then near the circle’s
APRIL 1 - 15                                 center is modestly bright Cor
   Mars remains in the west                  Caroli, a grand yellow-and-vi-      the right from the belt, you           here, he’s already walking
during and just after twi-                   olet double star in a telescope.    come to Aldebaran, now with            westward on his way to de-
light, as it will continue to do             It’s in the dim constellation       Mars above or to its upper             parting into the sunset come
through May. But now it has                  Canes Venatici, the hunting         right.                                 summer.
an interesting partner. You                  dogs.                                  Meanwhile, the Big Dipper
may have noticed the Pleiades                   And the star at the bend         is assuming its highest posi-          Alan MacRobert is a senior edi-
cluster descending toward it for             of the dipper’s handle, Mizar,      tion after dark, floating upside       tor of Sky & Telescope.

          6                                14                     20                       27
MARCH

          10:04 am                         5:27 am                8:43 pm                  11:10 pm                       Moon phase times
                                                                                                                              are for the

          5                                12                     19                       26
                                                                                                                          Central Time Zone.
APRIL

          3:50 am                          2:06 pm                6:12 am                  5:18 pm

                                                                                                                                               S t a r D a t e 11
How to use these charts:                                                                                                                                                                          February 20                                                            11 p.m.
       1. Determine the direction you are facing.                                                                                                                                                        March 5                                                                10 p.m.
       2. Turn the chart until that direction is at the bottom.
                                                                                                                                                                                                         March 20                                                                8 p.m.*
                                                                                                                                       NORTH
                                                                                                                                                                                                        * Daylight Saving Time begins March 10.

                                                                                                                                                CE PH EU S                                              A
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                                                                                                                                           SOUTH

   12         MARCH/APRIL 2019
How to use these charts:                                                                                                                                                                                            March 20                                                                                     11 p.m.
 1. Determine the direction you are facing.                                                                                                                                                                          April 5                                                                                      10 p.m.
 2. Turn the chart until that direction is at the bottom.
                                                                                                                                                                                                                     April 20                                                                                      9 p.m.
                                                                                                                                                   NORTH

                                                                                                                                                  A ld e
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                                                                                                                                                                                                                                                                                                                               TAU RU S
EAST

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                                                                                                                                                   SOUTH

                                                                                                                                                                                                                                                                                                                  S t a r D a t e 13
Astro Miscellany

                                 The Arecibo radio dish; Right:
NSF/NAIC ARECIBO OBSERVATORY

                                 A colorized version of the 1974
                                 message; Bottom: Teams must
                                 turn this sequence of numbers
                                 into an 18-character password

                                                                                                                                                                   WIKIPEDIA
                                 to enter the contest.

                           A New Message for the Galaxy
                               L
                                      ike a person updating          The Arecibo Observatory,        numbers 1-10, information       the competing teams must
                                      her voicemail greet-         which operates a 1,000-foot       about DNA, a figure of a per-   be accompanied by a nar-
                                      ing, the radio observa-      radio telescope in Puerto         son, and details on the Are-    rative that explains why the
                               tory that beamed the first          Rico, beamed out the origi-       cibo telescope.                 message is important, ad-
                               greeting from Earth into            nal message on November             The new message will          dresses possible risks of send-
                               space is getting ready to           16, 1974. It was designed by      be composed by one of 45        ing it to another civilization,
                               update the message. It has          Frank Drake, a pioneer in the     teams that make the initial     and provides such practical
                               started a contest that calls on     search for extraterrestrial in-   cut. To reach that point, the   details as where to aim the
                               groups of students — from           telligence, with help from as-    teams must decode a pass-       telescope (the first message
                               kindergarten through grad-          tronomer and science popu-        word that allows them to        was beamed toward M13, a
                               uate school — to prepare            larizer Carl Sagan. It consist-   enter the contest and solve a   globular star cluster 25,000
                               their own greetings to other        ed of 1,679 ones and zeroes       puzzle about a mystery in the   light-years from Earth).
                               civilizations. The winning          arranged in a grid of 73 rows     telescope control room, then       The winner will be an-
                               message will be transmitted         and 23 columns. Among             register by late March.         nounced on the September
                               in November.                        other details, it included the      Completed messages by         equinox.

                                                                                                       www.areciboobservatory.org/challenge

                           00000000000000000000000000000000000000000000000000001010
                           10001110010101000111001010100011100101010000100010101001
                           11110101010101110110101010111011010101010101101000101110
                           11010001011101101000101110110100010101011010001010101100
                           00000101001000000010100100000001010010000000101001000000
                           01010010000000101001000000010100100000011011000000000000
                           00000000000000000000000000000000000000000
                               14       MARCH/APRIL 2019
Picturing a Destiny in Space
U     ntil Surveyors and Mariners and Voyagers
      began beaming back close-range pictures of the
worlds of the solar system, most Americans saw the
                                                                            teamed with rocket pioneers Willy Ley and Wernher
                                                                            von Braun to publish a book and a series of maga-
                                                                            zine articles that showed how humans could expand
Moon, Mars, and other worlds through the eyes of                            into the solar system.
Chesley Bonestell, an architect, designer, and artist.                         The documentary, which premiered last year, in-
   Bonestell and his work are profiled in a docu-                           cludes clips of Bonestell himself, as well as interviews
mentary that will appear at several venues this                             with rocket scientists, filmmakers, artists, and other
year. “Chesley Bonestell: A Brush With the Future,”                         notables, who discuss his influence on our concept
chronicles his career and his influence on space                            of worlds beyond our own.
exploration.
   Bonestell began painting depictions of the Moon                          UPCOMING SHOWINGS:
and planets, rockets, and other space-related sub-                          March 24       The Filoli Estate, Woodside, California
jects in the 1930s. His work appeared in maga-                              March 27-31    Sonoma International Film Festival
zines and books and in “War of the Worlds,” “Des-                           April 23       Mount Diablo Astronomical Society, Walnut Creek, Calif.
tination Moon,” and other classic sci-fi movies. He                         July 18        Wings Over the Rockies Museum, Denver

                                                                            www.chesleybonestell.com/home.html

                                              Getting to Know the Moon Bit by Bit
                                              M      ore than 30,000 years ago,
                                                     the Aurignacians, the earliest
                                              modern humans in present-day Eu-
                                                                                          Sky at Night, it is a compendium of
                                                                                          just about every Moon-related topic.
                                                                                            Aderin-Pocock talks about observ-
                                              rope, notched a series of holes and         ing the Moon, the history of moon-
                                              crescents in a short segment of ea-         watching (including the Abri Blan-
                                              gle’s bone. The bone was discovered         card calendar), the Moon in folklore
                                              in the early 20th century at Abri           and science fiction, the history of
                                              Blancard, a rock shelter in France.         lunar exploration, lunar science,
                                              Decades later, an archaeologist con-        and the possible future commer-
                                              cluded that the notches represented         cialization of lunar resources, from
                                              the phases of the Moon, and that the        water and solar power to helium-3,
                                              bone was the earliest known lunar           a possible fuel for nuclear fusion
                                              calendar.                                   reactors.
                                                People have been recording the              Although each section is brief, it
    The Book of the Moon                      Moon ever since, on walls, moun-            provides a thorough overview of
    A Guide to Our Closest Neighbor
                                              tainsides, canvases, video screens,         each topic without getting bogged
    By Maggie Aderin-Pocock
    Penguin Books, $24.99 (April 1)
                                              and especially paper. One of the lat-       down in too much detail. So read-
    www.abramsbooks.com/                      est is The Book of the Moon: A Guide        ers can learn about everything from
    product/book-of-the-                      to Our Closest Neighbor. Written by         moonquakes to H.G. Wells to lunar
    moon_9781419738494                        Maggie Aderin-Pocock, a scientist           volcanism to werewolves in a quick,
                                              and host of BBC television’s weekly         easy package.

                                                                                                                                S t a r D a t e 15
As a successful planet-hunting
                                spacecraft came to the end of its
                                mission, a successor took flight.
                                Several others are expected to
                                follow in the next decade

                                By Rebecca Johnson
NASA AMES/JPL-CALTECH/T. PYLE

                                                                    NASA AMES

                                16   MARCH/APRIL 2019
O
            n October 30, NASA announced that its pre-                                           work through all of them.
                                                                                                    Borucki “converted me from a skep-
            mier planet hunter, Kepler, had run out of fuel                                      tic to a true believer” in the concept,
            and could no longer conduct science. A few                                           Cochran says. Cochran served as co-
                                                                                                 investigator on “all four proposals that
            weeks later, the agency sent its final com-
                                                                                                 got turned down, until the fifth one was
mands to the spacecraft, severing its communication                                              successful,” he recalls.
link with Earth. Kepler’s mission ended on November 15,                                             By the time Kepler launched, astrono-
                                                                                                 mers had found a few handfuls of planets
388 years to the day after the death of its namesake, the                                        orbiting other stars using ground-based
astronomer Johannes Kepler. The spacecraft is now drift-                                         telescopes (using a different technique
ing in a safe orbit around the Sun, 94 million miles from                                        from Kepler). So the question of whether
                                                                                                 other planets were out there — long be-
Earth. After nine years and thousands of planets, Kepler                                         lieved, but never proven — had been an-
is passing the torch to newer planet hunters.                                                    swered. But there weren’t nearly enough
                                                                                                 known planets to do any kind of statis-
                                                                                                 tical studies — to know the variety of

K
        epler began its journey with a             team found a workaround, which in-            planets or their parent stars.
        night launch from Cape Canaver-            volved allowing the spacecraft to change         Kepler produced a torrent of new plan-
        al on March 6, 2009. It soon began         its field of view every few months. A new     et discoveries. By early February, 2,662
searching for planets around other stars           mission, called K2, then began as Kepler      planets discovered with Kepler have been
by looking for transits. In these events,          continued hunting planets, now all across     confirmed, and a roughly equal number
a planet passes in front of a star, briefly        the sky. All told, the spacecraft probed      of candidates await confirmation. About
eclipsing a small portion of the star’s sur-       more than half a million stars for orbiting   3,000 scientific papers based on Kepler
face, causing it to grow a tiny bit fainter.       planets.                                      research have been published so far.
  Over its 3.5-year primary mission, Ke-              What the spacecraft found has changed         “Kepler has shown that virtually all
pler kept a constant eye on the light of           the picture of planets in our galaxy.         of the stars that we see in the sky prob-
150,000 stars in the constellations Cyg-              “When we started conceiving this mis-      ably host planetary systems,” Cochran
nus and Lyra. The mission’s larger goals           sion 35 years ago we didn’t know of a sin-    says. “Now we are discovering that a
were to use this sample to extrapolate             gle planet outside our solar system,” says    significant number of those systems are
the total number of Earth-like planets in          Bill Borucki, who created the Kepler con-     very much like our own and may have the
the Milky Way galaxy, and to better un-            cept and served as the mission’s original     capability of being habitable.”
derstand the characteristics of other solar        principal investigator, based at NASA’s          After launch, Cochran and his team at
systems to help scientists put our own in          Ames Research Center in California.           McDonald Observatory, along with as-
context.                                              McDonald Observatory research pro-         tronomers at other observatories around
  Soon after its primary mission ended,            fessor Bill Cochran worked with Borucki       the world, conducted follow-up obser-
Kepler’s science halted when one of its            on planning the mission, discussing the       vations to confirm or disprove Kepler’s
reaction wheels, which helped keep it              scientific and technical hurdles they         discoveries. Their observations could dis-
                                                                                                                                                    NASA GSFC/FRANCIS REDDY

pointed at its target, failed. The Kepler          would have to overcome and helping to         tinguish between a genuine planet transit
                                                                                                 and other behaviors in stars that can
The planet K2-288Bb, seen at bottom in this artist’s concept, orbits two red dwarf               mimic it, such as starspots.
stars. It’s the latest find in the Kepler data archive. Left: Kepler and TESS hunt                  This ground-based work studies these
for planets using the transit method, looking for a dip in a star’s light output that            stars in a completely different way than
indicates a planet is passing in front of it. Far left: This artist’s concept shows how          Kepler, using a technique called the “radi-
Kepler’s field of view changed positions across the sky during the K2 mission.                   al velocity” method. It entails monitoring

                                                                                                                               S t a r D a t e 17
the star’s motion toward and away from                          Kepler’s landslide of discoveries has                 not exist in our own solar system.
         Earth to detect any wobbles caused by the                    helped astronomers learn a lot about                       Other solar systems often have many
         gravitational pull of orbiting planets.                      planets in the Milky Way.                                planets orbiting very close to their parent
           The McDonald observations helped                              There are more planets than stars in                  stars, making our solar system look sparse
         confirm the first Earth-sized planet orbit-                  the Milky Way, for example, and small                    in comparison. While our system has four
         ing in the habitable zone of a star (Ke-                     planets are common. In fact, as many as                  small, rocky planets close to the Sun,
         pler-22); the most Earth-like planet yet                     half of the stars in the Milky Way may                   some have as many as eight planets with-
         seen orbiting another star (Kepler-452);                     have small, rocky planets orbiting in                    in the same distance. Astronomers want
         the first multi-planet system orbiting a                     the habitable zone, the distance from a                  to know if these packed-in planets formed
         binary star (Kepler-47); a system of six                     star where temperatures are just right for               close to their parent stars, or formed far-
         planets, some near-Earth-sized, orbiting                     liquid water to exist on a planet’s surface              ther out and later migrated inward.
         in the habitable zone of a star (Ke-                         — a likely prerequisite for life, at least life            Kepler’s findings provide a tantalizing
         pler-11); and an ancient system of five                      as currently understood.                                 beginning for future exoplanet searches.
         Earth-sized planets that dates to the dawn                      Planets come in diverse forms. And the                  “Now that we know planets are every-
         of the Milky Way galaxy (Kepler-444).                        most common form, which appears to be                    where,” Borucki says, “Kepler has set us
                                                                      between Earth and Neptune in size, does                  on a new course that’s full of promise for
                                                                                                                               future generations to explore our galaxy.”
                                                                                                                                 Indeed, one of Kepler’s successors is
                                                                                                                               already hard at work.
                                                                               Artist concepts of HD 21749b (left)

                                                                                                                               K
                                                                               and a lava world like LHS 3844b
                                                                                                                                       epler’s immediate follow-up mis-
                                                                                                                                       sion was launched from Cape Ca-
                                                                                                                                       naveral April 18. As its name in-
                                                                                                                               dicates, the Transiting Exoplanet Survey
                                                                                                                               Satellite (TESS) is searching for planets
NASA/2

                                                                                                                               using the same transit method as Kepler.

         TESS Logs Busy Start
                                                                                                                               What’s different is the types of target
                                                                                                                               stars. While Kepler looked at faint stars
                                                                                                                               between 300 and 3,000 light-years away,

         T
                   ESS began logging exo-       23 times the mass of Earth but          exploding stars.                       TESS is studying closer stars that are 30
                   planet discoveries just      only three times Earth’s diameter,         Some of its planet hunting and      to 100 times brighter.
                   a few months after its       which places it in the same cat-        astrophysics work overlap.                Over its initial two-year mission, TESS
         launch. By late January, it had        egory as Neptune, the outermost            For example, it discovered          will survey about 200,000 nearby red-
                                                                                                                               dwarf stars, covering an area of sky 400
         discovered eight confirmed plan-       of the Sun’s major planets. It’s        a planet orbiting the star HIP
                                                                                                                               times larger than Kepler did. Red dwarfs
         ets and almost 350 additional          separated from its star by just 20      116158. It also used a technique       are smaller and cooler than the Sun, but
         candidates. It also recorded more      percent of the Earth-Sun distance,      called asteroseismology to dis-        they are the most common type of star in
         than two dozen exploding stars,        though, so its surface is too hot to    cover dozens of sets of vibrations     the galaxy.
         flares on the surfaces of red-         be inhabited by Earth-like life.        on the star’s surface, which are          Astronomers at McDonald Observa-
         dwarf stars, and scores of other           A second, unconfirmed, planet       caused by the motions of gas and       tory are planning to follow up TESS
         flickering objects.                    in the system appears to be about       other processes deep within the        planet discoveries, too. A new instrument
             “The torrent of data is starting   the same size as Earth but about        star. The vibrations revealed that     for the Hobby-Eberly Telescope, one of
         to flow already,” said George          2.5 times as massive, making it a       the star is 1.2 times the mass of      the world’s largest optical telescopes, has
         Ricker, TESS principal investigator,   “super-Earth.”                          the Sun and 2.9 times its diam-        been designed to study red-dwarf stars
         during a press conference at the           LHS 3844b is an Earth-sized         eter, about 4.9 billion years old,     and their potential planets. Called the
         American Astronomical Society          world orbiting a stellar pipsqueak      and that it’s beginning the transi-    Habitable Zone Planet Finder (HPF), it
                                                known as a red dwarf. Although                                                 is being commissioned now.
         meeting January 7 in Seattle.                                                  tion to its red-giant phase, when it
                                                                                                                                  Michael Endl is a senior research sci-
         “TESS is going to be a robust          the star is a faint ember, the          will get much bigger and brighter.
                                                                                                                               entist at McDonald Observatory who
         planet finder and a supernova          planet, whose mass has not yet             The combination of observa-         has worked on Kepler follow-up with
         machine,” added Thomas Bar-            been determined, is so close to it      tions, along with follow-up work       Cochran, as well as projects using ground-
         clay, a mission scientist at NASA’s    that “it’s probably a lava world,”      from the ground, then produced         based telescopes to look for planets
         Goddard Space Flight Center.           said Chelsea Huang, a mission sci-      a dossier on the planet, which is      around red dwarfs. He was involved in
             One of the most recent dis-        entist at the Kavli Institute at MIT.   classified as a “hot Saturn”: It’s     the discovery of Proxima b, the planet
         coveries is HD 21749b, orbiting            TESS also has discovered            about 9.2 times Earth’s diameter       orbiting the nearest star to the Sun, a red
         a small, cool star about 53 light-     many other types of astronomi-          but 60 times Earth’s mass, so it’s     dwarf called Proxima Centauri.
         years away. The planet is about        cal objects, including dozens of        big and fluffy.                DB         “TESS and HPF are working together,”
                                                                                                                               Endl says. “TESS announces a candidate,

         18          MARCH/APRIL 2019
NASA ARC/J. DOTSON/W. STENZEL

                                                                                                                                                                                   NASA (2)
                                                                                                                                W
                                and then everybody jumps to follow up.”         A graphic from December 2017 (left) shows                  ith Kepler, the study of exo-
                                  TESS has begun to return some results         how Kepler provided a landslide of planet                  planets got its first motherlode
                                (see sidebar). Its planets should be close      finds (yellow) compared to missions before                 of data, providing key new in-
                                enough to Earth for astronomers to begin        and since (blue, purple). Technicians prepare   sights. And now it’s time for the new kids
                                looking for signs of life using spectroscopy    TESS for its April 18 launch (right).           on the block to make their contributions.
                                — spreading the light from the planet                                                              “As NASA’s first planet-hunting mis-
                                into its component wavelengths to look          large, bright, and relatively far from their    sion, Kepler has wildly exceeded all our
                                for chemical elements and compounds             parent stars.                                   expectations and paved the way for our
                                in its atmosphere that could have been             Because missions can take decades of         exploration and search for life in the solar
                                produced by living organisms.                   planning and technology development,            system and beyond,” said Thomas Zurbu-
                                                                                space agencies are already planning mis-        chen, associate administrator of NASA’s

                                A
                                          few more planet-hunting and           sions with exoplanet-studies goals that         Science Mission Directorate. “Not only
                                          -studying spacecraft are sched-       won’t launch until well into the next           did it show us how many planets could
                                          uled to launch soon.                  decade or beyond.                               be out there, it sparked an entirely new
                                   CHEOPS (CHaracterizing ExOPlanets               WFIRST (Wide Field InfraRed Survey           and robust field of research that has
                                Satellite) is a joint project of the European   Telescope) will take on multiple sci-           taken the science community by storm.
                                Space Agency (ESA) and the Swiss Space          ence missions. In addition to studying          Its discoveries have shed a new light on
                                Office, with the participation of several       dark energy, it will study exoplanets in        our place in the universe, and illuminated
                                other nations. Set to launch in October or      a couple of ways. First, it will conduct a      the tantalizing mysteries and possibilities
                                November from the Guiana Space Center           survey by staring at a dense region of stars    among the stars.”
                                on the South American coast, its mission        toward the center of the galaxy to look
                                will last at least 3.5 years.                   for brightenings caused when two stars          Rebecca Johnson is editor of StarDate.
                                   Unlike Kepler or TESS, which use sur-        exactly align. Such alignments, called
                                veys of many stars to discover exoplanets,      microlensing events, also reveal the pres-
                                CHEOPS will study systems with already
                                known planets. Specifically, it will target
                                                                                ence of planets around the stars, and mis-
                                                                                sion planners expect WFIRST to detect
                                                                                                                                Resources
                                exoplanets smaller than Saturn that orbit       more than 2,000 worlds. The telescope           Internet
                                bright stars with orbital periods of less       also will take direct images of perhaps 50      Exoplanet Exploration
                                than 50 days. By zeroing in on such a           planets around other stars.                     http://exoplanets.nasa.gov
                                specific set of exoplanets, mission plan-          Europe’s PLATO (PLAnetary Tran-              Kepler & K2
                                ners hope to narrow down the structure          sits and Oscillations of stars) mission is      http://nasa.gov/kepler
                                of these planets and figure out how they        scheduled to launch in 2026. It’s a follow-
                                formed and evolved.                             up to CHEOPS, and will build on that            TESS
                                                                                                                                http://nasa.gov/tess
                                   James Webb Space Telescope (JWST)            mission’s findings. “With PLATO, we
                                is another near-term space mission that         are focusing on Earthlike planets orbit-        JWST
                                will follow up on known exoplanets.             ing in the habitable zone around other          http://jwst.nasa.gov
                                Unlike CHEOPS, though, it’s not made            stars which are similar to our Sun,” said       CHEOPS
                                exclusively for planet work. JWST, which        Johann-Dietrich Wörner, director gen-           http://sci.esa.int/cheops
                                currently is scheduled for launch in 2021,      eral of ESA. “This will be a major step
                                                                                                                                WFIRST
                                will study a wide range of phenomena in         towards finding another Earth.”                 http://wfirst.gsfc.nasa.gov
                                infrared light, including in-depth follow-         A few years later, ESA will launch
                                up observations of exoplanets. The tele-        ARIEL (Atmospheric Remote-sensing In-           PLATO
                                scope will take spectra of these planets        frared Exoplanet Large-survey). This satel-     http://sci.esa.int/plato
                                to study their atmospheres. It may even         lite is designed to study the atmospheres of    ARIEL
                                be able to take images of planets that are      a diverse group of about 1,000 exoplanets.      http://sci.esa.int/ariel

                                                                                                                                                              S t a r D a t e 19
by Damond Benningfield and Rebecca Johnson

Resetting the Clock on Saturn’s Rings
B
        eauty is ephemeral.           the rings and Saturn itself.         ring, the D ring, “rains” into      could make the rings vanish in
           Consider, for example,       Previous estimates of the age      Saturn’s upper atmosphere.          as little as 100 million years.
        the rings of Saturn.          of the rings have varied widely,     Much of this falls toward the          Researchers also used obser-
These bands of ice and dust           with some suggesting the rings       equator. (The D ring may be         vations of Saturn’s rings to de-
are among the most beautiful          are as old as Saturn itself.         resupplied by material from the     termine the length of the plan-
features in the solar system,           The trajectory measure-            next ring out, the C ring.)         et’s day: 10 hours, 33 minutes,
yet they could be short lived.        ments showed that the rings             Cassini found, however,          38 seconds.
Recent research suggests they         are about 40 percent the mass        that a substantial amount of           Scientists have been unable
are no more than 100 mil-             of Mimas, a small moon of            material rains toward higher        to determine the rate of Sat-
lion years old, and could disap-      Saturn, or roughly half the          latitudes, roughly 45 degrees       urn’s rotation because there
pear in as little as 100 million      mass of the ice sheet cover-         north and south of the equa-        are no solid landmarks on the
years more — a mere blink             ing Antarctica. According to         tor.                                gas-giant planet to follow. At-
in the planet’s 4.5 billion-year      models of ring formation, the           When researchers combined        tempts to determine the rota-
lifetime.                             low mass suggests a recent ori-      the Cassini observations with       tion rate using variations in
   The Cassini spacecraft pro-        gin — probably in the last 10        some older views of Saturn          Saturn’s magnetic field yielded
vided new details on the rings        million to 100 million years.        from a ground-based telescope,      estimates that varied by as
during the last phases of its         The rings probably formed            they found changes in the           much as 10 minutes.
13-year reconnaissance of the         when a small comet or one or         planet’s ionosphere, an elec-          Cassini scientists, though,
Saturn system, which ended            more small moons passed too          trically charged layer of the       determined that the rings reso-
when the craft plunged into           close to Saturn. The planet’s        atmosphere. The changes may         nate to motions deep within
Saturn’s atmosphere in Sep-           powerful gravity pulverized the      be caused by bits of ice in the     Saturn itself, creating waves
tember 2017. Cassini passed           unlucky progenitor. Over time,       rings falling toward Saturn.        that ripple through the rings.
between Saturn and the inner          collisions ground the debris to      The particles have their own        The waves were difficult to sep-
edge of the rings during each         smaller and smaller particles,       electric charge, so they’re guid-   arate from waves caused by the
of its 22 final orbits of the giant   which spread out to form the         ed by Saturn’s magnetic field.      gravitational influence of Sat-
planet. The rings’ minuscule          magnificent rings.                   As they hit the atmosphere,         urn’s moons, but careful anal-
gravitational pull allowed sci-         Today, the rings consist pri-      they wash away particles of         ysis revealed the waves caused
entists to “weigh” them more          marily of tiny bits of ice, with a   haze, leaving dark bands de-        by the planet’s own gravita-
precisely than ever before. The       smattering of dust and pebbles.      tected by the ground-based          tional field, yielding what the
passages also provided a close        Some of the material at the          observations. The researchers       researchers say is the best mea-
view of interactions between          inner edge of the closest major      calculated that this icy rain       surement of Saturn’s day. DB

     A Cassini view of the
     rings, with Saturn in
     the background
                                                                                                                                              NASA/JPL/SSI

20        MARCH/APRIL 2019
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