Life on Mars?
Life on Mars? |
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Peter Neivert, MGS / MOLA,
NASA
Larger illustration.
Ancient Mars may have
had an ocean more than
two billion years ago
(1999
and
2007
news releases).
Since Mars has only 11 percent of the Earth's mass and only a little over a third of its surface gravity, Mars has been losing its internal heat much faster than Earth. As a result, it is much less geologically active than the Earth and has also lost much of its original atmosphere and possibly water to be lost to space. While many scientists have looked for signs of life from Mars' early history when the planet was more hospitable to Earth-type life, some have more recently been search for signs of life that yet exist, most likely in wet places underground, away from Mars’ harsh surface. (See a very brief overview of major events in Mars' planetary environment.)
Breaking News
On December 10, 2007, NASA announced that it has been working with a team called the International Mars Architecture for Return of Samples (IMARS) -- a committee of the International Mars Exploration Working Group (IMEWG) formed in 1993 to coordinate Mars exploration missions -- to developing plans and seeking recommendations to launch the first Mars mission to bring soil samples back to Earth. IMARS includes representatives from more than half a dozen nations and agencies (including NASA, the European Space Agency, the Canadian Space Agency, and the Japan Aerospace Exploration Agency), and other space-faring nations are welcome to join. IMARS participants will now perform a series of mission design studies before reconvening in March 2008 (NASA press release).
Signs of Life?
In papers published in 2006 and 2007, two planetary scientists speculated that microbes relying on a mixture of hydrogen peroxide (H2O2) and water (H2O) in their intracellar fluid might be able survive the thin, cold, dry atmosphere on Mars. Life that uses hydrogen peroxide has been found to exist on Earth (i.e., bombardier beetles and the soil bacterium Acetobacter peroxidans), and such life would be better able to absorb what little water is available from the rarified Martian atmosphere. Such life may also be consistent with the ambiguous results coming out from the life-detecting experiments aboard the 1970s Viking Landers; to date, no purely chemical explanation for the results of the Viking life-seeking experiments has been found, nor is there an explanation for the gas exchange experiment (which released carbon dioxide (CO2) and molecular nitrogen (N2) and oxygen (O2)), the pyrolitic release experiment (which broke down organic material), and and the labeled release experiment. An interesting ramification, however, is that H2O2 life would probably be easily killed by liquid water. (For more discussion, see: Lee Pullen, November 26, 2007; Doug Ellison, August 24, 2007; Astronomy Picture of the Day; and Houtkooper and Schulze-Makuch, 2007 and 2006).
MSSS,
JPL,
NASA
Larger and
full
model images.
NASA's 1970s Viking landers
may have detected microbes
that use a mix of hydrogen
peroxide and water for their
intracellular fluid
(more).
On February 21, 2005, Vittorio Formisano, chief scientist for Mars Express's Planetary Fourier Spectrometer (PFS), announced that the Elysium Planitia (whose southern region has evidence of pack ice in a dust-covered frozen sea) is the region of Mars observed to have the most methane (CH4) coming out of the surface. Since most of the methane in Earth's atmosphere is produced by microbes living in the soil, Formisano ventured that life is the most likely explanation for methane in the Martian atmosphere as well. In September 2004, Formisano reported that concentrations of water vapor near the Martian surface are two to three times higher along Elysium Planitia and two other regions near the equator, than at higher latitudes. Although methane may be more concentrated in that area, other scientists note that its presence may be a product of geological activity since Elysium Planitia is one of the major volcanic regions on Mars. On February 24, 2005, however, Formisano announced the detection of sufficient amounts of formaldehyde (CH2O), mostly likely from the oxidation of methane, which suggest that the annual emission of methane into the Martian atmosphere is too great to be produced by any known geological processes (Mark Peplow, news@nature.com, February 25, 2005).
ESA,
Mars Express,
DLR/FU Berlin
(Gerhard
Neukum)
Larger pack-ice and
area images.
Methane has been detect over Elysium Planitia,
whose southern part has dust-covered, pack
ice from a five-million-year-old sea
(New
Scientist
and
BBC).
Methane in the Martian atmosphere was previously detected by NASA's Infrared Telescope on Hawaii and the Gemini South Observatory in Chile on Earth (abstract from Krasnopolsky et al, 2004). Methane persists for only a short time in the Martian atmosphere before being broken down by photochemical processes within 440 Earth years from the intense ultraviolet radiation found on Mars because of the lack of a ozone layer. As a result, this greenhouse gas must be being constantly replenished by either active volcanoes, none of which have been found yet on the Red Planet, or microbes -- such as Earth's methanogens which produce methane from hydrogen and carbon dioxide and do not need oxygen to thrive. Indeed, the presence of methane with other gases such as oxygen is being considered as an indicator of Earth-type on extra-Solar planets. In July 2004, scientists assessing data from the Mars Express indicated that they may have found traces of ammonia, which is also an indicator of Earth-type biological activity although volcanoes can also be a source (more at news@nature.com and BBC News). On September 20, 2004, the ESA announced that the Mars Express detected overlapping concentrations of methane with water vapor in the planet's atmosphere, particularly over concentrations of underground water ice, which may be the result of biological activity (ESA press release).
Taylor Perron,
UC BerkeleySigns of Ancient Life?
In 1996, a team of scientists led by David McKay announced the discovery of possible fossil and trace chemical evidence for ancient microbacterial life in a chunk of meteorite (3.9-billion-year-old ALH840001) that came from the planet Mars. In February 2001, at least two teams of researchers announced finding chains of magnetite crystals similar to those made by bacteria on Earth in ALH84001 and in at least two other Mars meteorites that range in age from 1.3 billion to 165 million years (NASA Astrobiology Institute and BBC new briefs). In February 2006, a team of researchers announced the discovery of a mix of carbon compounds filling tiny veins in the Nakhla Martian meteorite which exhibits similarities with those found in fractured volcanic samples from the Earth's ocean floor raising the possibility that bacterial life produced the Martian material (McKay et al, 2006; and Gibson et al, 2006).
NASA
Possible fossil Martian
microbacteria
in meteorite ALH 84001.
Although the evidence has not been confirmed or become widely accepted, the announcements have helped to re-focus research into the possibility of life arising on planets circling other stars as well as in the Solar System. As with many "ground-breaking" discoveries, however, the gathering evidence raise more questions than they answer. Discussion of the latest findings and research papers can be found at the NASA-sponsored, Lunar and Planetary Institute. More information and films about the possibility of life on MARs also can be found at NASA's Mars Image Gallery.
Other Information
Try the NASA Astrobiology Institute (NAI).
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