Methane on Titan and Enceladus: Nature vs. Nurture?

In other recent work on Titan’s methane, scientists have modeled the process by which methane gas moves from the interior to the atmosphere and determined the time it takes for the methane to be lost to space. It turns out that about 60 to 180 million years ago, Titan could have had up to 3 to 4 times the amount of methane now observable there. That period, covering a time when large dinosaurs either flourished or were breathing their last on Earth, is believed to have been the start of the most recent period of major methane outgassing on Titan, when stores of methane gas in Titan’s interior began to be released to the surface. That is about the time when the methane seen on Titan today started to take center stage in Titan’s modern environment, shaping the landscape into the hazy, dune- and lake-dotted world Cassini is revealing to us today. Whether Titan had a constant or intermittent supply of methane in its much more distant past remains an outstanding question.

Central to these findings are data Cassini collected on the ratio of heavy hydrogen, or deuterium, to ordinary hydrogen in both Titan’s atmosphere and Enceladus’ plume. Variations of the deuterium-to-hydrogen ratio in organic compounds, and in water, provide clues to a planet or moon’s evolution, including the loss of gases that contain hydrogen.

Data used in the study came from the Cassini Ion and Neutral Mass Spectrometer and the Composite Infrared Spectrometer along with data returned in 2005 from the Huygens Probe’s gas chromatograph-mass spectrometer as it descended via parachute to Titan’s surface. Five of Cassini’s flights through the plume of Enceladus provided measurements of the same kind of isotope ratios.

As scientists discover more about the processes that led to the formation of bodies throughout our solar system, they can better understand how the Earth formed—and the likelihood that planets akin to Earth might form elsewhere in the cosmos.

This Cassini Science League entry is an overview of a science paper authored, or co-authored, by at least one Cassini scientist. The information above was derived from the following publications:

1) “A primordial origin for atmospheric methane of Saturn’s moon Titan,” Olivier Mousis (University of Arizona and Université de Franche-Comté, France); J. I. Lunine, Matthew Pasek (University of Arizona); Daniel Cordier (Institute de Physique de Rennes and Ecole Nationale Superieure de Chimie de Rennes); J. H. Waite, Jr., Kathleen Mandt, William Lewis, Mai-Julie Nguyen (Southwest Research Institute (SwRI) San Antonio), Icarus, Volume 204, Issue 2, p. 749-751.

2) “Formation conditions of Enceladus and origin of its methane interior,” Olivier Mousis (University of Arizona and Université de Franche-Comté,); J.I. Lunine (University of Arizona); J.H. Waite, Jr., B. Magee, W.S. Lewis, K.E. Mandt (Southwest Research Institute (SwRI), San Antonio, Texas); D. Marquer (Université de Franche-Comté, France); D. Cordier (Institute de Physique de Rennes and Ecole Nationale Superieure de Chimie de Rennes, France), Astrophysical Journal, Aug. 10, 2009

3) “Isotopic evolution of the major constituents of Titan’s atmosphere based on Cassini data,” K. Mandt, J. H. Waite, Jr., William Lewis, Brian Magee, Jared Bell (Southwest Research Institute, San Antonio, Texas), Jonathan Lunine, (University of Arizona); Olivier Mousis (University of Arizona and Université de Franche-Comté, France),; Daniel Cordier (Institut de Physique de Renne and Ecole Nationale Superieure de Chimie de Rennes); Planetary and Space Science, accepted June 10, 2009

4) “Liquid water on Enceladus from observations of ammonia and 40Ar in the plume,” J. H. Waite Jr, W. S. Lewis, B. A. Magee (Southwest Research Institute (SwRI, San Antonio, Texas.); J. I. Lunine (University of Arizona); W. B. McKinnon (Washington University, St. Louis, Missouri_; C. R. Glein (Arizona State University); O. Mousis (University of Arizona and Observatoire de Besançon, Besançon Cedex, France); D. T. Young, T. Brockwell, J. Westlake, M.-J. Nguyen, B. D. Teolis (SwRI, San Antonio, Texas); H. B. Niemann (NASA Goddard Space Flight Center, Greenbelt, Maryland); R. L. McNutt Jr., M. Perry (Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland); W.-H. Ip (National Central University, Taiwan),Nature 460, 487-490 (23 July 2009)

5) “Detection of 13CH3D on Titan,” Bruno Bezard (LESIA, Observatory of Paris, University of Paris, Diderot); Conor A. Nixon (University of Maryland); Isabelle Kleiner (LISA, University of Paris and CNRS); Donald E. Jennings (NASA Goddard Space Flight Center, Maryland) Icarus, (Note), 14 July, 2007

-- Mary Beth Murrill, Cassini science communication coordinator