Michael J. Mumma on Mars as a Possible Abode for Life
Fast Breaking Commentary, August 2010
Article Title: Strong Release of Methane on Mars in Northern Summer 2003
Authors: Mumma, MJ;Villanueva, GL;Novak,
RE;Hewagama, T;Bonev, BP;DiSanti, MA;Mandell, AM;Smith,
Michael J. Mumma talks with ScienceWatch.com and answers a few questions about this month's Fast Breaking Paper paper in the field of Space Science.
Why do you think your paper is highly cited?
We report the first definitive detection of methane gas on Mars. The atmosphere of Mars is highly oxidized, consisting mainly (95%) of carbon dioxide gas. With a photochemical lifetime of only 400 years, methane should not be present unless it was released recently. On Earth, methane is produced mainly (>95%) by biology, with a much smaller amount produced by geochemistry.
The presence of methane on Mars demonstrates that Mars is an active planet, now releasing trace gases that provide a window on internal processes.
Does it describe a new discovery, methodology, or synthesis of knowledge?
We describe the release of methane during Northern Summer on Mars, and its subsequent rapid removal—both results are surprising. The release occurs over regions rich in sub-surface hydrogen and also over an ancient volcanic construct. The seasonal nature of this release suggests thermal control of the release mechanism.
After three Earth years, one-half of the released methane had vanished. This rapid removal of methane requires a mechanism faster than photochemistry by a factor of about 100.
These discoveries have changed our view of Mars as a possible abode for life. But, the released methane could also be produced deep underground by geochemical processes such as serpentinization.
This paper has triggered major responses from atmospheric scientists and biologists.
Would you summarize the significance of your paper in layman's terms?
"Observation of Mars in Northern Summer..."
"The methane plumes on Mars..."
"Subsurface structure envisioned for Mars..."
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The release of methane on Mars suggests that Mars might now harbor an active microbial community below the surface. Or, it might now be releasing methane produced by reactions of hot rock with water and carbon dioxide deep underground. Either way, Mars is now revealed as an active planet that presents the possibility of using the escaping gases as tracers of internal processes.
This discovery challenges the current view of Mars as a "dead" planet, and demonstrates that we can learn much about Earth by studying Mars. The extreme life forms now living deep below Earth's surface—and fueled ultimately by hydrogen gas instead of photosynthesis—could have cousins living on Mars.
How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?
My Ph.D. dissertation research (in molecular physics and atmospheric sciences) coincided with the early attempts to explore Mars with spacecraft. Before then, the nature of Mars was virtually unknown and still quite mysterious. The 19th century views of astronomer Percival Lowell (abundant water, canals, widespread vegetation) were as yet untested, until the first spacecraft images (Mariner 4, in 1965) revealed Mars as a heavily cratered object that was clearly not Earth-like.
Mariner 9 was the first spacecraft to orbit the planet, and by mid-1972 it had revealed Mars as a dry non-vegetated planet. The Viking missions in 1976 conducted detailed searches for near-surface microbial life, but the consensus is that none was found.
Meanwhile, astronomers sought gases that could be produced by life on Mars. On Earth, biological processes produce methane so most Mars searches targeted its detection as a possible biomarker. Successive searches since 1969 used ever more sensitive instruments and telescopes, pushing the detection limits to levels far below those of terrestrial methane.
My Team achieved the first definitive detections in 2003 by using infrared spectroscopy from the summit of Mauna Kea, Hawaii, and the Mars Express orbiter obtained an indication of methane in 2004.
We reported our results at several conferences, but we became increasingly concerned about subtle instrumental effects that emerged as our analysis improved. Finally, we discarded the approach used, and started anew. We developed an entirely fresh set of analytical procedures that removed the instrumental artifacts completely and revealed multiple spectral lines of methane, along with carbon dioxide and water on Mars.
Our measurements of water and carbon dioxide (detected simultaneously with methane) show excellent agreement with measurements by instruments on Mars-orbiting spacecraft. We published our results in 2009.
Where do you see your research leading in the future?
In August 2009, we began the next phase of our investigation. Through June 2010, we used three major ground-based telescopes to map Mars in multiple gases over a major portion of the Mars year. We will continue such surveys in future apparitions and with future instruments as they become available.
Prior to our discovery, budgetary issues had stalled the Mars Exploration Programs of both Europe and the United States. Our discovery triggered NASA and ESA to combine their Mars exploration programs, initiate the Trace Gas Orbiter mission (to be launched in 2016), and re-open plans for a joint surface exploration by two landed rovers in 2018. These missions were long envisioned to search for signs of life at sites where ancient geochemical signatures suggest local conditions on early Mars were amenable to life. They are important.
However, the full exploitation of active regions requires a different path. First, we must find all sites of active release, quantify the composition of gases released from each, and determine which of them repeat their release annually on Mars. This multi-dimensional database will permit us to distinguish those sites that are driven by geochemistry alone, from those that could also harbor biology.
Next, we must conduct deep searches for active life forms at the most promising sites of each type, using instruments on landed rovers. Finally, if complex organics indicating life are found by the landers, a return to Earth of materials collected from such sites is essential.
Do you foresee any social or political implications for your research?
Our discovery triggered immediate near-term social and political impact. NASA and ESA re-ignited and combined their Mars Exploration Programs, reversing a recent trend to de-emphasize Mars exploration. The extended response is likely to be even more significant.
By establishing Mars as a possible abode for life, our results could have profound social and political implications. If carried to the extreme, our results identify a pathway to finding extant life on our fellow planet. The discovery of life on Mars would provide an opportunity to determine whether life on Earth and Mars shared a common heritage, or diverse. The ability to study life-form(s) from Mars would provide profound insights into the nature of life itself—we could gain new perspectives about ourselves through that process.
Dr. Michael J. Mumma
Solar System Exploration Division
NASA Goddard Space Flight Center
Greenbelt, MD, USA
KEYWORDS: METHANE, MARS, ORIGINS, WATER VAPOR, INFRARED SPECTROMETRY, MARTIAN DUST DEVILS, MU-M, OXIDANT ENHANCEMENT, ATMOSPHERE, LIFE, CH4, HABITABILITY, SPECTRUM.
Figure 1: Observation of Mars in Northern Summer, 2003, when the solar longitude (Ls) was 155°. (a) Aspect of the planet. The sub-solar and sub-Earth points and several conspicuous geologic features are marked, and the spectrometer entrance slit (NASA-IRTF) is shown to scale (vertical lines). With this geometry, spectra are acquired simultaneously for 35 spatial footprints along the slit. (b) Spectrum acquired at 70°N latitude is shown (top). Spectral signatures of Mars methane (CH4) and water (H2O) appear after subtraction of terrestrial and solar signatures. The depth of the spectral lines is shown in a grayscale representation extending over the latitude range 70°N to 70°S on the planet (bottom, two panels). Spectral lines of water (three lines) and methane (one line) are strongest in the northern hemisphere (frame of b). The latitudinal distribution of methane alone appears (frame of c) after subtracting a synthetic model of H2O. Two other spectral lines of methane (R0 and P2) and several other lines of water were detected and mapped at nearby spectral settings. Credits: G. L. Villaneuva, M. J. Mumma, and R. E. Novak.
Figure 2. The methane plumes on Mars in Northern Summer 2003. Credits: M. J. Mumma, G. L. Villaneuva, and the NASA GSFC Visualization Studio.
Figure 3: Subsurface structure envisioned for Mars. (a) The sub-permafrost region may vent gases as pores open and close seasonally at scarps. (b) Schematic showing possible thermal mechanism for controlling seasonal release of gases. (After M. J. Mumma et al., Strong release of methane on Mars in Northern Summer 2003, Science, 323:1041–1045, 2009, and NASA).