Titan’s Greenhouse Effect and Climate: Lessons from the Earth’s Cooler Cousin
A White Paper Submission to the NRC Planetary Science Decadal Survey
Conor A. Nixon1,*, Athena Coustenis2, Jonathan I. Lunine3, Ralph Lorenz4, Carrie M. Anderson5, F. Michael Flasar5, Christophe Sotin6, J. Hunter Waite Jr.7, V. Malathy Devi8, Olivier Mousis9, Kim R.
Reh6, Konstantinos Kalogerakis10, A. James Friedson6, Henry Roe11, Yuk L. Yung12, Valeria Cottini1, Giorgos Bampasidis13, Richard K. Achterberg1, Nicholas A. Teanby14, Gordon L. Bjoraker5, Eric H.
Wilson6, Tilak Hewagama1, Mark A. Gurwell15, Roger Yelle3, Mark Allen6, Nathan J. Strange6, Linda J. Spilker6, Glenn Orton6, Candice J. Hansen6, Jason W. Barnes16, Jason M. Soderblom3, Vladimir B.
Zivkovic17, Anezina Solomonidou13, David L. Huestis10, Mark A. Smith3, David H. Atkinson18, Patrick G. J. Irwin14, Mathieu Hirtzig2, Simon B. Calcutt14, Timothy A. Livengood5, Sandrine Vinatier5,
Theodore Kostiuk5, Antoine Jolly19, Nasser Moazzen-Ahmadi20, Darrell F. Strobel21, Mao-Chang Liang22, Patricia M. Beauchamp6, Remco de Kok23, Robert Pappalardo6, Imke de Pater24, Véronique
Vuitton25, Paul N. Romani5, Robert A. West6, Lucy H. Norman26, Mary Ann H. Smith27, Kathleen Mandt7, Sebastien Rodriguez28, Máté Ádámkovics24, Jean-Marie Flaud29, Kurt K. Klaus30, Michael
Wong31, Jean-Pierre Lebreton32, Neil Bowles14, Marina Galand33, Linda R. Brown6, F. Javier Martin-Torres12, Brook Lakew5, Shahid Aslam34.
1Univ.
Maryland, *conor.a.nixon@nasa.gov, 2Obs. Paris, 3Univ. Arizona, 4APL, 5NASA GSFC, 6Caltech/JPL, 7SWRI, 8Coll. Wm. and Mary, 9Obs. Besançon, 10SRI, 11Lowell Obs., 12Cal. Inst. Tech, 13Univ. Athens, 14Univ. Oxford,
15Harvard-Smithsonian, 16Univ. Idaho (Physics), 17Univ. N. Dakota, 18Univ Idaho (E.Eng.), 19LISA Univ. Paris, 20Univ. Calgary, 21JHU, 22Academica Sinica, 23SRON, 24UC Berkeley, 25Lab. Plan. Grenoble, 26UCL, 27NASA LRC,
28CEA/Univ. Paris, 29LISA/CNRS, 30Boeing, 31STScI, 32ESA/ESTEC, 33Imperial Coll. London, 34MEI Technologies.
ABSTRACT
3. SEASONAL CHANGE: SMILE OR FROWN?
4. THE FATE OF THE ATMOSPHERE
• The Decadal Survey for Planetary Science conducted by
the Space Studies Board of the US National Academies,
recently issued a call for white papers, to inform
prioritization of future funding for research, including
missions. This poster summarizes our submitted paper.
• Titan experiences an ~30 yr seasonal cycle due
to its orbital inclination.
• Titan’s upper atmosphere functions as a vast chemical factory, turning the
raw materials (N2, CH4, H2O) into more complex molecules and haze.
• Imaging in 1992 showed a ‘smile’: a bright upturned arc in the southern hemisphere at red
wavelengths. Blue images showed the opposite:
a bright northern hemisphere.
• These condense and fall from the atmosphere, causing an irreversible
depletion of methane. The CH4 inventory will last just ~107 Myr, unless
resupplied: perhaps by volcanism, outgassing, or cometary impacts.
• We show here that Titan is an atmospheric ‘greenhouse
world’, like the Earth, Mars and Venus.
• In 2002 the trend was reversed, with a
‘frowning’ bright (red) north.
• Study of Earth’s planetary ‘cousins’, including Titan, has
great potential to inform us about the nature of the
greenhouse effect and long-term climate change on our
world.
• See the final box for our recommendations on how best to
address this important topic.
1. GREENHOUSE EFFECT: HOW DOES IT WORK?
• This seasonal ‘migration’ of haze from south to
north and back is caused by a summer-pole-towinter-pole circulation in the stratosphere.
• MESSAGE: Titan experiences seasons with
parallels to the Earth. Modeling these changes
is a useful test of terrestrial models: including
physical, chemical and dynamical processes.
Image: R. Lorenz/STScI
2. ANTI-GREENHOUSE EFFECT
• Key molecules in Titan’s
atmosphere are more
transparent to visible light
than to infrared radiation.
• An opposing anti-greenhouse
effect cools the atmosphere.
• This is mainly due to stratospheric
haze particles that are transparent
to infrared but absorb visible light.
• When sunlight reaches
Titan’s surface, some reradiated thermal energy is
trapped, warming the lower
atmosphere and surface.
• A feedback loop also
exists, whereby small
increases in H2, which is not
limited by saturation,
causes more CH4 to be
retained in the atmosphere,
increasing and amplifying
the warming.
• The net result of the positive (+23
K) and negative (-11 K) greenhouse
effects is +12 K, raising the surface
temperature from 84 K to 94 K.
• Compare to the Earth (+30 K),
Venus (+500 K) and Mars (+5 K).
Titan Atmosphere Schematic. Credit: ESA
At least 12 haze layers are seen on this
Cassini ISS image at 10°S. (NASA/JPL/SSI)
• MESSAGE: Titan’s greenhouse
effect resembles the Earth’s. By
studying Titan we can better
understand the Earth’s
atmospheric processes.
• If all CH4 is removed, then
the atmosphere may
periodically collapse and
freeze out on the surface.
• MESSAGE: Titan is a case
study in climate change. By
investigating Titan’s fate, we
can better appreciate how
the Earth may undergo
natural or anthropogenic
climate change.
Graphic: NASA TSSM Final Report/J. Lunine.
OUR RECOMMENDATIONS:
To advance critical research into Titan's climatology - simultaneously
advancing our understanding of the Earth’s atmosphere - we advocate to
the NRC Decadal Survey for Planetary Science the following steps:
1. Endorse: the strong positive findings of the recent Senior Review of the
Cassini Solstice Mission, to continue the mission until 2017.
2. Urge that a successor Titan-focused mission be given very high priority
for near-term development and launch.
3. Recommend continued funding for strong ground-based, airborne and
space-based observing campaigns for continuous, long-term Titan
monitoring.
4. Support continued funding for applicable NASA R&A programs and the
NSF Planetary Astronomy Program; and for associated laboratory
experiments, modeling and theoretical calculations.
5. Propose that a dedicated NASA outer planetary flagship mission
program be initiated, analogous to the Mars and lunar programs, to
encompass the continued operations of Cassini, and follow-on flagship
missions.
For more information, including electronic downloads of this poster and the full white paper, please visit: http://www.astro.umd.edu/~nixon/titanclimate.html