Jovian Wrapup - Uranus and Neptune - Uranus was discovered by accident Neptune was found via predictions from gravitational physics.
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Jovian Wrapup – Uranus and Neptune
● Uranus was discovered by accident
● Neptune was found via predictions from gravitational
physics.
Uranus Neptune
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William Herschel's Discovery of Uranus
● In 1781 William Herschel noticed a moving object
(moving night-to-night) that he supposed was a comet.
● He reported the “comet” and people around the world
began to observe it.
– They soon realized that the object was in a circular orbit
around the Sun beyond Saturn – a new planet!
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Neptune's Discovery
● By the mid-1800's Uranus had completed an orbit
around the Sun since its discovery.
– Astronomers noted that it was not quite following the path
predicted by Newton's physics and gravitation
– It was likely that a massive unknown planet beyond Uranus
was tugging Uranus off of its expected path.
– Working backwards English mathematician Adams and
French mathematician LeVerrier independently calculated
the location of the unknown planet.
– LeVerrier contacted astronomers in Berlin who found
Neptune within an hour of the start of the search (only a
finger's width away from the predicted position).
Adams
LeVerrier
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Uranus and Neptune
● Uranus and Neptune are Jovian worlds dominated by
Hydrogen/Helium mantles.
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Uranus and Neptune
● Jupiter and Saturn have “solar” composition.
– Uranus and Neptune are more dominated by ice (and rock).
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Uranus and Neptune
● Jupiter and Saturn have “solar” composition.
– Uranus and Neptune are more dominated by ice (and rock).
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Uranus and Neptune
– Methane gas absorbs red light but lets blue light pass into
the atmosphere, off the particulates, and back to us giving
them their blue-green color.
– Since they are colder than Jupiter and Saturn the high white
clouds are made of methane ice crystals.
8 Uranus and Neptune
9
Uranus and Neptune
● Uranus and Neptune both have systems of thin rings
Infrared views
reveal/exaggerate
the Uranian rings
since the planet is
quite dark at these
wavelengths.
Visible light views
hardly show them
at all.
10
Uranus and Neptune
● Uranus and Neptune both have systems of thin rings11
Uranus and Neptune
● Uranus and Neptune both have systems of thin rings
Neptune's Rings12
Uranus/Neptune Wrapup
● Uranus and Neptune both have systems of icy moons13
Uranus/Neptune Wrapup
● Uranus and Neptune both have systems of icy moons14
Triton
● Triton is a
Pluto-sized
world with a
“youthful” icy
surface.
● It holds on to
a thin nitrogen
atmosphere.
● It orbits
Neptune
“backwards”
and is likely a
captured
cousin of Pluto15
Triton
● Like Enceladus and the
Uranian satellites,
Triton is dominated by
water/ice and is rich in
volatiles like ammonia,
nitrogen and methane.
This mix enables
geological activity at
the frigid temperatures
of the outer Solar
System with only
modest interior
warmth.
● Triton is likely to be
representative to what
Frozen lakes on Triton?
we will find when we
arrive at Pluto in 2015.16
Triton's Atmosphere, Ice Caps and Geysers
● Triton's south pole is just coming out of a decades-long winter
where it is so cold the thin nitrogen atmosphere has frozen solid
on the surface.
● The dark streaks arise from nitrogen/ice geysers that shoot
material into the atmosphere.
● The nitrogen atmosphere freezes out at the poles in winter.
Warmed in the summer, the gas bursts out from below the frozen
surface layers.17
● The dark streaks arise from nitrogen/water/ice
geysers that shoot material into the
atmosphere.18
Pluto: Major Planet or Minor Nuisance?
● Pluto/Charon is a double world at the outskirts of the
Jovian Planet region of the Solar System19
Pluto: Major Planet or Minor Nuisance?
● Smaller than the Earth's Moon, it's status as a “major”
planet, secure for 70 years, was recently lost.20
Pluto: Major Planet or Minor Nuisance?
● From its discovery in 1930 until its demotion in 2006
Pluto was regarded as one of nine major planets in the
Solar System.
Pluto and its
satellite Charon21
Pluto: Major Planet or Minor Nuisance?
● The formal definition of Pluto as a “dwarf planet” by the
International Astronomical Union in 2006 brought
strong reaction from both astronomers and non-
scientists.22
Pluto: Major Planet or Minor Nuisance?
● The formal definition of Pluto as a “dwarf planet” by the
International Astronomical Union in 2006 brought
strong reaction from both astronomers and non-
scientists.23
If you want to understand the issues surrounding Pluto's
planetary status, then you first must understand...
Solar System Debris:
Comets and Asteroids
● Primarily found in two zones in the solar system.
The Asteroid The
Belt (rocky, Edgeworth/Kuiper
between Belt (beyond
Jupiter and Mars) Neptune) and
Oort Cloud (way
out there) –
sources of comets
(icy)24
Solar System Debris
● Why do comets and asteroids exist?.... Solar system
formation is a messy process.25
Solar System Debris
● During the accretion of the planets, the planets sweep
up and fling out most of the debris but stable/protected
zones remain.26
Solar System Debris: Asteroids
● Jupiter interfered with the formation of a planet
between Mars and Jupiter. Some fraction of the debris
remains today as the asteroid belt.
– Jupiter stirred up the planetesimals so that collisions were violent
rather than gentle.27
Asteroids
● Asteroids are small, rocky, cratered and irregularly
shaped.
– They are the collisionally modified remains of leftover
planetesimals between the orbits of Mars and Jupiter.28
Asteroids
● Asteroids are small, rocky, cratered and irregularly
shaped.
– They are the collisionally modified remains of leftover
planetesimals between the orbits of Mars and Jupiter.29
30
Asteroids
● Asteroids are small, rocky, cratered and irregularly
shaped.
– They are the collisionally modified remains of leftover
planetesimals between the orbits of Mars and Jupiter.31
Asteroids
● Millions of these objects orbit in the Asteroid belt –
staying between Mars and Jupiter.
– Some have orbits that cross the inner planets.32
Asteroids
● Millions of these objects orbit in the Asteroid belt –
staying between Mars and Jupiter.
– Some have orbits that cross the inner planets.33
Asteroids
● Some asteroids are “binary” objects.34
Asteroids
● The original “parent bodies” that were the predecessors of
the asteroids were large enough to differentiate.
– some asteroids are metallic, consisting of the core fragments of a
large parent body.
– the largest asteroids may be intact parent bodies. The DAWN
mission, now in orbit around Ceres targets two of the largest – Ceres
and Vesta.35
The Dawn Mission
● The Dawn spacecraft, launched in 2007,
arrived at Ceres (2011) and will travel on
to Vesta (arriving in 2015).36
The Dawn Mission
● Ceres and Vesta are thought to
represent substantially intact
planetesimals from the early Solar
System.37
Vesta from Dawn
Click on the image for a movie of Vesta's rotation38 Vesta from Dawn
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Asteroids and Meteorites
● Meteorites that fall to Earth are just small asteroids. They
tell the story of the differentiation and fragmentation of
the asteroids.
– Some are entirely metallic, some are stony, some appear to come
from unmodified undifferentiated objects.40
Asteroids and Meteorites
● Meteorites that fall to Earth are just small asteroids.
They tell the story of the differentiation and
fragmentation of the asteroids.
– Some are entirely metallic, some are stony, some appear to come
from unmodified undifferentiated objects.41
Meteorites
● If you want to find a meteorite, go to a place on Earth
where Earth-rocks are rare.
– Antartica and the Sahara Desert are good choices.42
Asteroids and Meteorites
● Meteorites that fall to Earth are just small asteroids.
They tell the story of the differentiation and
fragmentation of the asteroids.
– Meteorites are often spectral fingerprint matches to distant
asteroids. You can hold a piece of Vesta in your hand with
certainty.43
Meteorites
● There are four major classes of meteorites
– Stones: rocky meteorites with iron flecks.
– Stones represent the majority of “falls” but are found in equal
numbers with “iron” meteorites.44
Meteorites
● There are four major classes of meteorites
– Stones tend to be composed of chondrules – glassy beads
making up most of the mass of the rock.
– Astronomers still argue about the origin of chondrules – how did
these glassy beads form during the formation of the Solar
System?45
Meteorites
● There are four major classes of meteorites
– Irons represent the other significant type of meteorite.
– Only about 6% of “falls” are irons, but they represent the
majority of “finds” because they are so recognizable as
something completely odd.46
Meteorites
● There are four major classes of meteorites
– Irons represent the other significant type of meteorite.
– When etched with nitric acid a crystalline patter appears in cross
sections of iron meteorites.
– This pattern can only arise from the slow cooling of molten iron
(one degree every million years) consistent with formation in the
center of a huge differentiated asteroid!47
Meteorites
● There are four major classes of meteorites
– “Stony-iron” meteorites (a.k.a. Pallasites) appear to have come
from the core-mantle boundary in a differentiated asteroid. They
are quite rare.48
Meteorites
● There are four major classes of meteorites
– “Carbonaceous chondrites are possibly the most interesting of
meteorites of all. They represent about 1% of falls.
– Carbonaceous chondrites are undifferentiated and largely
unprocessed. They must come from small parent objects too
small to become hot and melt and differentiate.
– Some carbonaceous chondrites contain amino acids formed in
the Solar Nebula – the building blocks of protiens.49
Meteorites
● Meteorites are important astronomically because they
represent material preserved from the time of the
origin of the Solar System.
– Recall that radioactive dating uniformly finds an age of 4.56
billion years for all of these objects.50
Pluto: Major Planet or Minor Nuisance?
● The formal definition of Pluto as a “dwarf planet” by the
International Astronomical Union in 2006 brought
strong reaction from both astronomers and non-
scientists.51
The Discovery of the Asteroids (ca. 1800)
● On January 1, 1801 an object (Ceres), much smaller
than the Earth's Moon, was discovered orbiting the Sun
between the orbits of Mars and Jupiter.
●
At first it was thought to be the 8th planet (only 7 were
known at the time), but...
– On March 28, 1802 another object (Pallas) was discovered in
nearly the same orbit, and another (Juno) in 1804, and yet
another (Vesta) in 1807.
– In 1828 textbooks listed 11 planets, however by 1851 twelve(!)
more of these objects had been found.
● Finally, in 1852, astronomers recognized these
“asteroids” as a separate class of object and went back
to a Solar System with eight planets (Neptune having
been discovered in 1846).
– The asteroids were tiny compared with the “classical” planets
See http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html52
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The Discovery of Pluto in 1930
● Pluto was discovered in 1930 during a deliberate search
for a planet beyond Neptune.
– When it was discovered it was thought to be larger than the
planet Mercury.
– All hailed it as the Ninth Planet in the Solar System.
– That designation stuck until 1992 when the first of hundreds of
similar objects were found orbiting the Sun beyond Neptune.54
Pluto's Stock Plummets
● By 2000 it was apparent that Pluto was simply the largest
object yet discovered in an outer (icy) asteroid belt.
– Astronomers counted the days until an object larger than Pluto was
discovered in this region.
– It happened with the discovery of 2003UB313 (now Eris) in 2003.
● Astronomers now had to cope with the issue. Was
2003UB313 Planet 10, or was it time to demote Pluto to
non-planetary status?
– In 2006 the vote was official – The Solar System has Eight planets.
Eris and
Dysnomia55
Pluto's Demotion
● The Solar System now officially contains 8 major
planets. Pluto, along with Ceres and Eris are “dwarf”
planets.
– The body that governs the naming of astronomical objects has
officially decided:
● "A planet is a celestial body that (a) has sufficient mass for its self-
gravity to overcome rigid-body forces so that it assumes a hydrostatic-
equilibrium (nearly round) shape, and (b) is the dominant object in its
local population zone, and (c) is in orbit around the Sun."56
Why Pluto Never Had a Chance
● Bottom line – the Solar System has Four
well defined zones
– The rocky terrestrial planets – Mercury,
Venus, Earth, Mars
– The asteroid belt
– The immense gas giant worlds – Jupiter,
Saturn, Uranus, Neptune.
– The outer icy asteroid (Kuiper) belt –
containing Pluto and hundreds of
thousands of other objects.57
But Pluto's Status as an Interesting World
has not Changed
● Pluto has a large moon, Charon, and an atmosphere.
– Two new smaller moons were discovered in 2005. One or maybe
even two even smaller ones turned up recently.
● The “New Horizons” spacecraft (the fastest thing ever
launched by Humans) will arrive in 2015.
– Pluto is getting farther from the Sun at present
– New Horizons hopes to arrive before the atmosphere freezes
out.58
Detecting Pluto's Atmosphere
● How do you tell that a world that is just a dot in a
telescope has an atmosphere?
– Watch it pass in front of a star...59
Spending on Space
● Guiding principle: All federal investments should
maximize societal benefit
● Direct return
– The information returned may directly benefit us all
● Protection against rogue asteroids
● Perspective on Earth climate
– Earth orbit is the ideal platform for Earth monitoring.
● Finding resources or a future refuge.... unfortunately not.
– Exploration for exploration's sake... the data themselves are
worth the cost.
● Products of space exploration (pictures of Titan) are of
intrinsic worth equal to expenditure.
– A definition/expectation of a great civilization.60
Spending on Space
● Guiding principle: All federal investments should
maximize societal benefit
● Indirect return
– Economic stimulus on steroids
– Note that NASA does not launch gold bars into space valued
at billions of dollars
● Funding spent on NASA ( ½ a percent of the federal budget)
gets spent here on the ground employing people and
developing our high-technology infrastructure.
– 100 times more than the NASA budget is already spent on
social programs. Savaging NASA would make the smallest
dent here on Earth.
● Of the $4 billion spent on the Cassini mission, the salvage
value of the spacecraft is maybe $100,000 the rest went
into jobs and technology development in the US.
● Even spectacular NASA failures (e.g. the recent Orbiting
Carbon Observatory) are economic successes.61
We Should Solve Our Problems Here on
Earth First
● This is exactly the outcome of spending on space
exploration.
– Development of new practical technologies (why do you
think you have an iPhone?)
– High quality highest-technology jobs here in the U.S.
– Significant budgetary multiplier – Every dollar of NASA
spending is estimated to provide several dollars of return
to the economy.
– Inspiration
● Fostering the next generation of scientists is possibly the
most important outcome of NASA spending
● Astronomy is the most visually compelling and thus instantly
inspiring of the sciences.
● If you want to lift a child out of poverty make him/her want
to be a scientist (and provide the opportunities to pursue
that goal – maybe the hardest part, back to social
programs....).62
Investing in the Future
– Today's high-tech society and its resultant wealth-generating
power can be tied in many ways to the significant
investment made in space exploration in the 1960s.
– How can we afford not to take as aggressive an approach to
science today??? We're not...63
Bottom Line(s)
● Investment in Space drives technology innovation
benefiting all of society.
– Technology is the ultimate engine of our economy in the
present era.
– World leadership is the outcome.
● Space Exploration, in many ways is the ultimate
economic stimulus.
● How can we afford NOT to invest in space exploration in
the midst of a recession or at any other time???You can also read
