The report examines extraterrestrial atmospheres, specifically focusing on Venus and Jupiter, while also addressing an interesting aspect of Earth's climate change related to methane release from melting ice. It discusses unique atmospheric phenomena such as greenhouse gases on Venus leading to extreme temperatures and the Great Red Spot hurricane on Jupiter. The analysis incorporates current research and findings to illustrate the significance of understanding these celestial atmospheres in atmospheric science.

1. Extraterrestrial Atmospheres
by Poruri Sai Rahul.
This report on `Extraterrestrial Atmospheres' is to accompany a presentation made
on the same as part of the course ME 5530 `Introduction to Atmospheric Science'. This
report contains 4 sections. In the Introduction, I mention what my motivation was to
choose this particular topic. In the subsequent sections on Venus and Jupiter, I brie
y
mention some of the interesting atmospheric phenomenon observed and current research
avenues being pursued to understand said phenomenon. Finally, in the last section on
Earth, I look at an interesting and usually neglected side eect of global warming i.e
release of trapped methane.
1 Introduction
Broadly speaking, the study of any extraterrestrial atmosphere is classi

2. ed as `Extrater-
restrial Atmospheric Science', ranging from planetary atmospheres to that of exo-planets,
the atmospheres of various moons and in a few cases, the atmospheres of comets and as-
teroids. As part of the course on `Atmospheric Science', we've studied the vertical pro

3. les
of pressure and temperature on Earth, clouds and rainfall, winds and brie
y, radiative
heat transfer and climate change. Much of the science we've learnt as part of the course
can be applied in a rudimentary fashion to understand extraterrestrial atmospheres. In
addition, extraterrestrial atmospheres present exotic phenomenon, a few of which ob-
served on Venus and Jupiter will be addressed later in this report. A study of such
phenomenon can lead to a better understanding of the underlying science and in general,
a deeper insight into Atmospheric Science in general.
1

4. 2 Venus
Venus is the closest planet to Earth, orbiting the Sun at 0.7 AU1. It's radius is 6051.8
kms, roughly 0.952 times that of Earth. It receives Solar Irradiance of 2613.9 W=m2,
roughly 1.911 times that of what Earth receives. Assuming a simple radiative heat
transfer model to balance the incoming solar radiation and the outgoing radiation from
the planet's surface, the black-body temperature of Venus is estimated to be 184.2 K. But
the surface temperatures on Venus have actually been recorded at 737 K2, far greater than
the estimated black-body temperature. Multiple reasons contribute to such extremely
high temperature conditions on the surface of Venus, the most important of which is
the eect of greenhouse gases. In stark contrast with that on Earth, the atmosphere on
Venus is largely comprised of CO2, a small amount of N2 and trace amounts of SO2,
Ar and CO. It is also worth mentioning that the concentration of water vapour in the
atmosphere of Venus is 20 ppm. CO2 is a common greenhouse gas and being present in
such large quantities lead to an extraordinary greenhouse warming in the atmosphere.
More recently, Ehrenreich et al. (2012) designed a new way to estimate the contribution
of CO2 towards atmospheric albedo of Venus. Venus has a Bond albedo3 which is 0.90,
2.94 times that of Earth's Bond albedo! In general, the authors have designed a new
way to understand the atmospheric transmission spectrum, ATS here forth, of Venus.
Obtaining the ATS of any atmosphere will help us understand the composition of the
atmosphere better. For example, in the case of Earth, the ATS is dominated largely by
Rayleigh scattering at shorter UV wavelength and by water vapour absorption bands in
the longer IR wavelengths.4 Fig. 1 illustrates a qualitative look at the ATS of Earth
and Fig. 2 illustrates the contribution of various components in the atmosphere towards
ATS. Understanding ATS has further applications in studying exo-planets, speci

5. cally
their atmospheres. This is what motivated the authors to develop this new method. The
authors intend on observing the atmosphere of Venus during it's transit of the Sun as
observed from Earth on June 2012. Such a Venus transit has happened earlier on June
2004 but will only be happening again in December 21175. Also note that in order to
measure an ATS, one needs a standard, calibrated radiator or emitter and what better
than our own Sun. The authors simulated how such an transit ATS will look by using
in-situ measurements of Venus made by the Venus Express6. Assumptions regarding the
atmosphere were made such as a variation only along the altitude and ignoring variations
along the latitudinal and longitudinal directions. The authors concluded that Rayleigh
scattering by CO2 molecules is a prominent contributor at heights of 70 kms above the
11 AU = 1 Astronomical Unit = distance between the Sun and the Earth.
2Russian probes Venera 13, 14, 15 and 16 landed on the surface of Venus and recorded surface
characteristics.
3Albedo can be quanti

6. ed using Bond albedo or Geometric albedo. Bond albedo looks at the entire
spectral range of emission, absorption and scattering, it is a more accurate measure of albedo.
4Water Vapour, as mentioned in class, is one of the lesser known greenhouse gases. Because of
it's peculiar electronic and molecular structure, the molecule can absorb emissions in a large range of
wavelengths in the IR regions leading to the ATS having a band structure.
5en.wikipedia.org/wiki/Transit of Venus
6Launched in November 2005 by the European Space Agency, Venus Express has been observing
Venus since April 2006 and is considered one of the most successful missions to Venus.
2

7. surface of Venus and Mie scattering as important between heights of 80-100 kms above
the surface. A complete spectral view is shown in Fig. 3.
An interesting fact about Venus which we haven't discussed so far is the fact that the
planet takes 243 days to rotate about itself. Just to remind oneself, it takes 24 hours of
1 day for the Earth to rotate about itself! It is speculated that Venus collided with an
asteroid or comet early on it's life, a collision that reduced it's angular momentum to such
a low value and causing retrograde rotation7. We are not interested in why Venus has such
a small rotational angular momentum. Rather, we are interested in it's consequences.
Such a long day-night cycle means that the same face on Venus is facing the Sun for a
large period of time, receiving a large amount of solar radiation! This could in-fact be
another reason for the extremely high temperatures on Venus. In fact, temperatures on
Venus is much larger than that on the day-side of Mercury, the closest planet to the Sun!
This extreme heating on one side of the atmosphere also leads to a phenomenon referred
to as Superrotation. The wind speeds measured in the upper atmospheric layers of Venus
are 90 m/s. In contrast, the fastest wind speeds measured on Earth are 113 m/s during
tropical cyclones and 135 m/s in tornadoes. Mind you, these events on Earth are transit
phenomenon where as the high wind speeds on Venus persist! The atmosphere is in fact
moving so fast that even though it takes 243 days for the planet to rotate about itself,
it only takes 4 days for the atmosphere to go around the planet! Hence referred to as
Superrotation. Superrotation is observed in only one other place in the solar system, on
Titan, one of Saturn's moons. Interestingly, while such high wind speeds are observed in
the upper layers of the atmosphere, the surface winds are of the order of . . . m/s, similar
to that on Earth. Such unique wind patterns make Venus an interesting case study to
understand winds in general. In fact, J. Peralta et al. (2014) I and II have in fact used
observations from the Venus Express mission to categorize the various types of winds on
Venus. The authors have been able to broadly distinguish them as
Acoustic Waves
Inertia-Gravity waves
Lamb waves
Surface waves, similar to those on Earth in the geostrophic regime.
Centrifugal waves, a special case of the Rossby waves arising from the cyclostrophic
approximation.
Following an understanding of the underlying wind patterns, Yamamoto and Takahashi
(2006) suggest meridional
ow as a possible cause for Superrotation whereas Durand-
Manterola (2010) attributes trans-terminator
ow as the cause!
I have tried providing a brief overview of the various exotic atmospheric phenomenon
observed on Venus I feel that a better understanding of the underlying science will
help us gain deeper insight into winds and in general, into Atmospheric Science.
7Retrograde rotation refers to motion in the direction opposite to the motion of a reference object,
in this case the motion of Venus around the Sun.
3

8. 3 Jupiter
Jupiter is the largest planet in the solar system, 371.83 times heavier than Earth and
only 0.09% that of the Sun! In astronomical terms 0.09% is a negligible amount. In
fact, it is commonly argued that Jupiter is a failed star. This argument is supported by
multiple observations made about the planet. The

9. rst being it's atmospheric composition
constituting 89.8% of H2 and 10.2% of He along with a few trace elements, a composition
similar to that of our own Sun or in fact any other star in this universe! The second
observation is the surface temperature of Jupiter, which is much higher than that expected
from solving radiative heat transfer! This is attributed to the fact that Jupiter has an
internal source of heat, speci

10. cally a source of heat that is gravitational in nature8.
Looking at Jupiter's atmosphere, the Hadley circulation cells we observe between vari-
ous latitudes on Earth are ampli

11. ed leading to the presence of bands on Jupiter stretching
large a latitude range. Interestingly, these bands also travel in opposite directions, caus-
ing eddies and vortices at the boundary layer due to shear between the bands! Another
observation on Jupiter, which we will be looking at in further detail, is the Giant red
spot on Jupiter. Fig. 4 shows a portion of Jupiter's band structure across latitudes and
the Giant red spot. It was taken by the Voyager 1 mission as it
ew by Jupiter in 1979.
The Great red spot, GRS here forth, is a hurricane of epic proportions! It's size is
24-40,000 kms E-W by 12-14,000 kms N-S9. To put those numbers in context, one could

12. t three Earths into that hurricane! The wind speeds observed at the boundary of the
GRS are 120 m/s, similar to that observed during the strongest hurricanes on Earth!
More interestingly, the GRS has been observed since 1665 i.e for almost 350 years! In
contrast, a hurricane on Earth can last a few weeks, maybe even a month in a few cases.
Although it is now observed to be shrinking, it's longevity is still a mystery. In fact, a
similar problem is faced by scientists trying to predict the longevity of a hurricane on
Earth where the the hurricane is observed to decay much slower than what is predicted
by theory or simulations! Hassanzadeh and Marcus (2013) have come up with a possible
explanation for the longevity of the GRS on Jupiter, attributing to meridional
ow as
the culprit. Their simulations showed that such a meridional
ow helped extract shear
energy from the adjacent bands to sustain the GRS. It is suggested that earlier simulations
didn't model the meridional
ow to sucient extent and that their model overcomes these
misgivings.
And to mention brie
y, Tsumura et al. (2014) implemented a new way to study the
ATS of Jupiter, a method similar to what was explained earlier in the case of Venus. The
authors observed the Jovian moons Europa, Callisto and Ganymede through Jupiter's
shadow and studied their spectra to infer properties about the planet's atmosphere! This
is an ingenious development as it removes the need for satellites to be sent all the way to
Jupiter to observe it's atmosphere!
8referred to as the Kevin-Helmholtz mechanism of heating in astronomical objects.
9en.wikipedia.org/wiki/Atmosphere of Jupiter#Great Red Spot
4

13. I have barely scratched the surface here, many more interesting features follow from
the references I've mentioned so far.
4 Back to Earth
Coming back to Earth, so far in the course we've looked at the causes of climate
change and the various eects it has, the primary of which is a drastic increase in mean
sea level. While an increase in mean sea level is a signi

14. cant threat to human life there
is another side eect of the melting of glacial and polar ice that hasn't been discussed
. Looking back, earlier in the course, we discussed the distribution of Carbon on Earth,
in the atmosphere, in the Earth's core and in polar glacial ice! We also measured
the rate of melting assuming a constant solar irradiance and a constant surface area for
ice. In reality, modelling the melting of ice is a tricky question as we need to take into
consideration the interaction between molten ice and ice! Water has a higher albedo than
ice does and therefore absorbs more heat than ice! . Therefore, when one is estimating
the rate of ice melting, one should consider the extra heat added by this molten ice!
Most of the carbon trapped in glacial and polar ice is in the form of methane. Once
glacial ice starts to melt, this trapped methane starts to leak up to the surface and
will escape into the atmosphere. Methane is a known greenhouse gas and an increase
in methane concentration will drive a positive feedback cycle that would cause further
heating, further melting and further release of harmful methane into the atmosphere!
This is an altogether neglected bit of information while discussing climate change.
Coming to the main point, glacial ice, speci

15. cally in Greenland, is melting faster than
ever before thanks to soot! We've discussed the positive, cooling eects of soot in the
Earth's atmosphere but soot only has a residence time of the order of a few weeks in the
atmosphere! It will therefore settle on the earth's surface eventually. It has now been
observed that large portions of ice on Greenland are now covered with soot! Soot, as we
know, has a high albedo and soot covered ice will therefore heat and melt faster. The
Dark Snow project led by Jason Box, is one of the teams studying the eects of soot on
glacial melting and mapping Greenland's surface to understand the extent of soot cover!
North-American and Russian forest

16. res, industrial exhaust and bio-waste management
are the major sources of soot in the atmosphere. Keegan et al. (2014) have studied,
independently, the melting of glacial ice on Greenland and looked for a correlation with
forest

17. res in the North American mainland. While anomalies do exist, there is sucient
evidence to suggest that soot deposits increase the rate of melting, lead to a longer period
of glacial melting, one that begins earlier ends later and in an overall larger loss of
ice cover! Bacteria have also been observed on the glacial ice surface, bacteria that were
previously unobserved and that increase the albedo of ice!Technological advancements
such as the use of unmanned aerial drones have helped survey a larger region of Greenland
and have helped survey it faster!
Climate change is one of the most pressing topics of our generation and technologi-
cal advancements expertise in various

18. elds need to be brought together in order to
5

19. understand it better and tackle it!
References
Ehrenreich et al. (2012)
J. Peralta et al. (2014) I and II
Yamamoto and Takahashi (2006)
Durand-Manterola (2010)
Tsumura et al. (2014)
Keegan et al. (2014)
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html
http://csep10.phys.utk.edu/astr161/lect/venus/features.html
http://csep10.phys.utk.edu/astr161/lect/jupiter/features.html
http://darksnow.org/
http://www.meltfactor.org/blog/?p=1329
6

20. Venus Earth Ratio
Radius(km) 6051.8 6356.8 0.952
Bond albedo 0.90 0.306 2.94
Solar irradiance (W=m2) 2613.9 1367.6 1.911
Black-body temperature (K) 184.2 254.3 0.724
Sidereal Orbit period (days) 224.701 365.256 0.615
Sidereal rotation period (hrs) -5832.6 23.9345 243.690
Surface pressure(bars) 92 1 92
Average temperature (K) 737 288 2.599
Table 1: Venus fact sheet
(by vol) Venus Earth
CO2 96.5% 400 ppm
N2 3.5% 78.08%
O2 - 20.95%
SO2 150 ppm -
Ar 70 ppm 9340 ppm
H2O 20 ppm -
CO 17 ppm -
He 12 ppm 5.24 ppm
Ne 7 ppm 18.18 ppm
Table 2: Atmospheric composition of Venus.
Jupiter Earth Ratio
Mass (1024 kg) 1898.3 5.9726 371.83
Radius(km)* 66,854 6356.8 10.517
Bond albedo 0.343 0.306 1.12
Solar irradiance (W=m2) 50.50 1367.6 0.037
Black-body temperature (K) 110.0 254.3 0.433
Sidereal Orbit period (days) 4332.589 365.256 11.862
Sidereal rotation period (hrs) 9.9250 23.9345 0.415
Surface pressure(bars) 1000 1 1000
Temperature (at 1 bar) (K) 165 288 0.572
Table 3: Jupiter fact sheet.
*Jupiter is an oblate planet and the polar - equatorial radii dier by a signi

21. cant amount.
(by vol) Jupiter Earth
H2 89.8% 0.55 ppm
He 10.2% 5.24 ppm
CH4 3000 ppm 1.7 ppm
NH3 260 ppm -
O2 - 20.95%
H2O 4 ppm -
Table 4: Atmospheric Composition of Jupiter.
7

22. Figure 1: Atmospheric transmission of Earth - a qualitative look.
Figure 2: Atmospheric transmission of Earth - component wise contributions.
8

23. Figure 3: Atmospheric transmission of Venus
Figure 4: Atmospheric bands and the Great red spot on Jupiter
9