Climate Change on Mars - By Peter J. Sherman Astrobiology, Harvard Summer School August 2011
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Climate Change
on Mars
By Peter J. Sherman
Astrobiology, Harvard Summer School
August 2011
Mars is the sole planet whose surface can be observed from Earth using a
telescope. Due to the clear view of the Martian surface from Earth, humans have
long been intrigued by the possibility of life in outer space. While the human
interest in extraterrestrial life has been existent for many centuries, viewing the
universe from Mars’ perspective had not been feasible until a few decades ago.
On July 14, 1965, NASA sent Mariner 4 to Mars. Mariner 4 was the first probe
sent by any space organization to successfully orbit Mars. From Mariner 4, we
learned about what we were dealing with on Mars; the images showed a
seemingly lifeless planet with craters that greatly ranged in size. Important to
note from the results was the low atmospheric pressure (4.1 to 7.0 mb) and
temperatures (-100 C) and the lack of a magnetic field on the surface of Mars
(http://www.astronautix.com/project/mariner.htm). Although Mariner 4’s planetary expedition occurred
just over 45 years ago, we have discovered much more about Mars through
more expeditions.
We have recently sent more probes to Mars to provide us with information
about the potentiality of life outside of Earth. These space missions have helped
to determine the characteristics of Mars and whether life could be sustainable.
Probes have found signs of erosion and liquid water on the surface of Mars.
With well-designed probes like these, we should be able to find even more
information about Mars.
Aside from NASA’s most recent discovery of craters forming salty, liquid
water just a few days ago, NASA was also recently baffled by the fact that parts
of Planum Australe, the Martian south pole, was evaporating into theatmosphere. Fenton 2007 compared two images taken by the Mars Global
Surveyor, one in 1977 and 1999 (http://www.skepticalscience.com/Climate-Change-on-Mars.html). It is known
Planum Australe is primarily composed of water ice and dry ice, with some parts
being permafrost and others being seasonal. Based on the two images 23 years
apart, NASA noted that not only the seasonal ice caps disappeared, but also
parts of the permafrost. The disappearance of parts of the permafrost ice caps
can best be attributed to the rapidly growing average surface temperature which,
in fact, has increased by an astonishing .5 C since 1970
(http://www.timesonline.co.uk/tol/news/uk/article1720024.ece), a rapid average climate change which is very
similar to that of ours on Earth due to global warming. If Mars’ atmosphere were
being blasted away by solar winds (due to its lack of a magnetic field), large
asteroids, and Mars’ own internal workings, Mars would deal with a significantly
weaker greenhouse effect; there would be less of an atmosphere to insulate the
rays from the sun on Mars. This would lead to a much colder Mars. The
stripping of the Martian atmosphere begs the question as to how it would be
possible for the average temperature to rise (at a fast rate) when all of its
insulation is rapidly disappearing.
Scientists have tried to determine possible reasons as to why the average
Martian temperature would rapidly increase despite a shrinking atmosphere.
People have attempted to explain this phenomenon through many different
theories, based off of the many characteristics of Mars and its history. These
theories run the gamut from solar irradiance on Mars to large global dust storms
which change the composition of Mars’ atmosphere. This research paper will goover possible theories for the increased average surface temperature and
determine the validity of each one. It will start by investigating dust storms and
strong winds due to Mars’ low thermal inertia and the Martian wobble (caused by
its tilt and rotation) as possible catalysts for the large climate change that
scientists have witnessed over the past 40 years. Then, it will look at how these
small changes in the Martian environment could have led to a lower albedo and
how that could have affected the Martian climate change. This researcher will
then determine the validity of these theories or whether Mars is heating up simply
because of solar irradiance, solar cycle variations which affect the average
temperature of all planets in the sun’s orbit. Solar cycles could be used to
explain Mars’ as well as Earth’s global warming as a natural occurrence – not
completely man-made. This paper will then proceed to determine the final
location of the evaporated Martian water from the polar ice caps, as we know
that, because of probes, water vapor is an extremely small component of the
Martian atmosphere. If the Martian atmosphere is composed of only a small
amount of water vapor, where is all the water vapor going if the polar ice caps
are evaporating? Finally, this paper will conclude with a discussion as to which
theory has the most validity to its claim. A variety of factors could have
potentially influenced the current climate change on Mars, but do some hold
more validity than others?
Mars has a low thermal inertia; when the sun shines on the surface, it
heats up quickly, and when the sun’s rays do not hit the surface, Mars cools
down almost immediately. The low thermal inertia of Mars can be seen thoughits daily temperature swings, which can have a range as large as 100 K per day
(http://en.wikipedia.org/wiki/Climate_of_Mars). Like on Earth, the temperature swings on the surface of
Mars lead to large windstorms –
significantly larger than that on Earth because
the temperature swings are much greater on
Mars. These large Martian windstorms
contribute two things to their environment; they
trap heat on Mars and they throw everything on the
Figure 1: This is an
surface of Mars around, image of Mars taken in like a Martian version of a
2001. In the bottom right
corner, a light patch of
tornado. The Martian brown can be seen, wind’s ability to trap heat
indicating a dust storm.
could be an explanation of http://en.wikipedia.org/wiki/File:Mars_ the beginning for Mars’
pits 1999.gif
rapid climate change. When the Mariner 9 probe first landed on Mars in 1971,
NASA noticed that all the images taken were difficult to see. The images were
unclear due to a large dust storm that encompassed a large portion of the planet.
We later found out that these dust storms are a frequent occurrence on Mars
because winds only need to be around 40-50 miles per hour to cause such
storms (http://en.wikipedia.org/wiki/Climate_of_Mars). Strong enough winds would shoot dust from
Mars’ surface into the air. This also occurs on Earth, but on Mars, the dust
becomes an important contributor to the atmosphere because there is more of it
and because of precipitation. On Earth, we are able to get rid of dust in our
atmosphere, before it can become a major contributor to the atmosphere
through, precipitation. This process of precipitation requires too warm a
temperature and too high an atmospheric pressure to currently occur on Mars.Therefore, while the dust thrown into the wind on Earth is cleaned out of the
atmosphere by precipitation, more dust on Mars (because there are stronger
winds) is left in the atmosphere. The combination of heat trapped by the large
surface winds and no loss of heat from the atmosphere (that is neither growing
nor shrinking because the Mars’ surface dust counters the affects of the Martian
atmosphere stripping) could be an explanation for the beginning of the increased
average surface temperatures on Mars since the late 1970s. This is an
extremely plausible theory because there are many images of large windstorms
on Mars, like in Figure 1, which indicate large quantities of dust being thrown into
the air all over the Martian surface. What other scientific theories have been
taken into account as possibilities for the climate change on Mars?
Every planet in our solar system experiences a wobble due to the
gravitational pull from the
sun with respect to its
tilt from the rotational axis.
Changes in the tilt, as
small as they may be, can
result in drastic climate
changes. Milutin
Milankovitch, a renowned
Serbian
mathematician, noticed that Figure 2: This diagram
Earth’s average surface
indicates the relation of
degrees to the change in
temperature in the
Vostok ice core in
Milankovitch cycles.
http://en.wikipedia.org/wiki/File:Milank
ovitchCyclesOrbitandCores.pngtemperature was directly related to its axial tilt from its orbital plane. As the axial
tilt decreases, the seasons have much milder temperatures because the sunlight
hits the entire surface of Earth with the same amount of power. This is the
opposite from when the axial tilt is large because the seasons will be extremely
polarized due to sunlight shining brightly on some areas of Earth and little on
others (http://www.universetoday.com/14894/mars-tilt/). Milankovitch addressed the relationship of
Earth’s axial tilt versus Earth’s average surface temperature, which had a period
of around 41,000 years (http://en.wikipedia.org/wiki/Milankovitch_cycles). This relationship is known as
Milankovitch Cycles, which are similar to a sinusoidal function. While Earth and
Mars are not entirely characteristically similar, similar cycles can be attributed to
Mars, as well. Mars’ axial tilt is currently increasing, which is making the
summers hotter and the winters colder. Martian seasons are about twice as long
as Earth’s seasons. With a hotter summer, the seasonal martian polar ice caps
on Mars evaporate into the atmosphere at a faster rate than usual. Even some
of the permafrost on Mars evaporates due to the strong effects of the axial tilt.
This could be a plausible explanation for the Martian climate change because the
summers would be hotter than usual, and the polar ice caps would evaporate into
the atmosphere.
A few other scientists believe that a change in solar irradiation was the
catalyst for climate change on both Earth and Mars. Solar irradiance is “the
amount of solar energy that arrives at a specific area at a specific time.”
(http://www.oilgae.com/ref/glos/solar_irradiance.html). Over the past few decades, some scientists have
noted a slight distinction in the amount of solar irradiation received by Earth,which varied by about .2% (http://en.wikipedia.org/wiki/Solar_variation#Solar_irradiance_of_Earth_and_its_surface). Comparing solar irradiation versus time, scientists saw a sinusoidal graph, as shown in Figure 3. In this belief of solar irradiation, the amount of power received is not the only thing changing; ultraviolet irradiance and solar winds are also greatly impacted. While there is a percent variation of just .2% for total irradiance, things such as UV irradiance have greatly changed over the past few centuries. The UV irradiance has increased by 4.3% since the Maunder Minimum (a period from 1645-1715 where sunspots were seldom seen by solar observers), and the sun’s magnetic flux has increased by a factor of 2.3 since 1901 (http://en.wikipedia.org/wiki/Solar_variation#Changes_in_total_irradiance). The increase of UV radiation and the sun’s magnetic flux over the past few centuries would be an indication of climate change, not just on Earth, but in our entire solar system. This means that all planets in our solar system would have a parallel global warming; everyone is increasing temperature at the same rate. A parallel global warming would concur with the evidence that Mars and Earth have increased average surface temperatures of about the same rate over the past 40 years. While this theory is backed by a few scientists, it is widely regarded as ludicrous by the majority of the scientific community. Aside from the many other reasons why this theory is a tad bit preposterous, this theory also claims that humans have no impact whatsoever on our current climate change on Earth. Not only does this theory make little physical sense, solar irradiance could also be attributed to the elliptical rotations of the planets around the sun. Although this theory receives censure from the large majority of the scientific community, the solar irradiance theory
agrees with both the wind- Figure 3: This graph
dust storm and axial tilt
shows the amount of
theories in that they show solar flux received per that Mars is rapidly heating
year. The function is
sinusoidal
up, and causing its polar ice caps to evaporate into
http://wattsupwiththat.com/2009/05/14
/the-solar-radio-microwave-flux/
the atmosphere. However Mars has an incredibly thin
atmosphere, and water vapor composes only .03% of its atmosphere
(http://www.daviddarling.info/encyclopedia/M/Marsatmos.html). Since Mars has a thin atmosphere and water
vapor is an infinitesimal portion of it, water vapor is, essentially, non-existent in
the Martian atmosphere. Where is the final destination of the evaporated water if
it is essentially not in the composition of the Martian atmosphere?
2GM
We have learned in class that v esc = . Although the radius of Mars
r
is about 50% of Earth’s radius, the mass of Mars is about 11% of Earth’s mass.
Using the equation, this means that the escape velocity is going to be
significantly smaller on Mars compared to Earth. A smaller escape velocity
means that a significantly larger amount particles are able to escape from the
Martian atmosphere in comparison to Earth’s atmosphere. In class, we have
3KT
also learned the equation vThermal = . Using 218 K as the average
m
temperature on Mars, we find that vThermal = 17.36800756 m/s. Using 3,376.2 kmas the radius of Mars and 6.4185 * 1023 kg, we can plug these variables into the
escape velocity equation. We find that vesc = 5027 m/s. Since the escape
velocity only needs to be six times greater than the thermal velocity, and
5027/17.36800756 = 289.2392482, water vapor is able to escape out of the
Martian atmosphere and into space. Will the disappearing ice have an impact on
the average surface temperature on Mars?
Since ice is a brighter surface than liquid water, it has a higher albedo.
Albedo is the reflectivity
of an object. The higher
the albedo an object has,
the less amount of light
the object can absorb.
The lower the refelectivity
the more the surface of
the object can heat up.
When Mars was given a slight heat boost from
Figure 4: This figure
either wind-dust storms, an increased indicates what happens axial tilt, or
when the albedo is
lowered. This occurred
solar irradiation, the seasonal ice, and on Mars through the even some of
original melting of ice.
the permafrost, began to melt. This http://maps.grida.no/go/graphic/ice-
decreased the
albedo-feedback-process
albedo of Mars because there was less ice covering
the surface. This in turn led to a rapid heating on the surface of Mars, and can
explain the .5 C increased temperature over the last 40 years. Now that weknow the end result of this whole process, which heating process makes the
most sense for Mars?
I believe that each of the three theories played a role, whether large or
small, in the process of evaporating ice on Mars. Certain concepts from each of
these theories could be an explanation for what has been a big question mark for
scientists over the past few years of noticing this change. Wind-dust storms, the
axial tilt, and solar irradiance could have all greatly been catalysts for the climate
change on Mars over the past few decades, which led to the lower albedo on
Mars. Climate change is becoming an important topic to discuss, not just for
Earth, but for Mars, as well.WORKS CITED 1. "Climate change hits Mars." The Sunday TImes. N.p., 29 Apr. 2007. Web. 8 Aug. 2011. . 2. Wikipedia contributors. "Climate of Mars." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 5 Aug. 2011. Web. 8 Aug. 2011. 3. Wikipedia contributors. "Solar variation." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 21 Jul. 2011. Web. 8 Aug. 2011. 4. "Global warming and climate forcing by recent albedo changes on Mars." Nature International Weekly Journal of Science (Feb. 2007): n. pag. Nature Publishing Group. Web. 8 Aug. 2011. 5. "Mars Melt Hints at Solar, Not Human, Causing for Global Warming, Scientist Says." National Geographic 28 Oct. 2010: n. pag. National Geographic. Web. 8 Aug. 2011. . 6. Cook, John. "Climate Change on Mars." Skeptical Science. N.p., 13 Mar. 2008. Web. 8 Aug. 2011. .
7. Wikipedia contributors. "Mars." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 7 Aug. 2011. Web. 8 Aug. 2011. 8. Barry, Patrick. "A Tale of Planetary Woe." NASA. N.p., 6 Nov. 2009. Web. 8 Aug. 2011. . 9. "Evidence for Recent Climate Change on Mars." Malin Space Science Systems. N.p., 6 Dec. 2001. Web. 8 Aug. 2011. . 10. Wikipedia contributors. "Milankovitch cycles." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 8 Aug. 2011. Web. 8 Aug. 2011. 11. Wikipedia contributors. "Solar variation." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 21 Jul. 2011. Web. 8 Aug. 2011.
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