Titan's Meteorology Over the Cassini Mission: Evidence for Extensive Subsurface Methane Reservoirs

Research areas:
Year:
2018
Authors:
  • E. P. Turtle
  • J. E. Perry
  • J. M. Barbara
  • A. D. Del Genio
  • S. Rodriguez
  • Stéphane Le Mouélic
  • Christophe Sotin
  • J. M. Lora
  • S. Faulk
  • P. Corlies
  • J. Kelland
  • S. M. MacKenzie
  • R. A. West
  • A. S. McEwen
  • J. I. Lunine
  • J. Pitesky
  • T. L. Ray
  • M. Roy
Journal:
GEOPHYSICAL RESEARCH LETTERS
Volume:
45
Number:
11
Pages:
5320-5328
Month:
JUN 16
ISSN:
0094-8276
Abstract:
Cassini observations of Titan's weather patterns over >13years, almost
half a Saturnian year, provide insight into seasonal circulation
patterns and the methane cycle. The Imaging Science Subsystem and the
Visual and Infrared Mapping Spectrometer documented cloud locations,
characteristics, morphologies, and behavior. Clouds were generally more
prevalent in the summer hemisphere, but there were surprises in
locations and timing of activity: Southern clouds were common at
midlatitudes, northern clouds initially appeared much sooner than model
predictions, and north polar summer convective systems did not appear
before the mission ended. Differences from expectations constrain
atmospheric circulation models, revealing factors that best match
observations, including the roles of surface and subsurface reservoirs.
The preference for clouds at mid-northern latitudes rather than near the
pole is consistent with models that include widespread polar
near-surface methane reservoirs in addition to the lakes and seas,
suggesting a broader subsurface methane table is accessible to the
atmosphere.
Plain Language Summary We monitored methane clouds in the atmosphere of
Saturn's moon Titan for over 13 years, using images from the Cassini
spacecraft. The observations cover almost half of Titan's year, showing
how weather patterns changed from late southern summer to northern
summer (approximately mid-January through late June on Earth). During
southern summer, extensive clouds and, on one occasion, rainfall were
observed near Titan's south pole. But surprisingly, this weather pattern
did not repeat at the north pole in northern summer. By comparing
weather observations to atmospheric models, we can determine sources for
the moisture in the atmosphere. Our analysis shows that, in addition to
Titan's lakes and seas, there may also be liquid beneath the surface
near both poles. This result is consistent with other evidence that
suggests there may be underground connections between some of the lakes
and seas. Knowing there may be more liquid below Titan's surface helps
explain how methane is supplied to the atmosphere and how Titan's
methane cycle works (similar to Earth's water cycle: evaporation, cloud
formation, rain, and surface collection into rivers, lakes, and oceans).
With the end of the Cassini mission, Earth-based telescopes will
continue to watch for large clouds on Titan.