Life on Mars?
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On May 30, 2012, scientists published a paper suggesting that a large portion of the atmospheric methane detected on Mars may have been generated by ultraviolet radiation of fallen carbonaceous meteorites. They based their hypothesis from experiments using samples from the Murchison meteorite (which has a high carbon content), which gave off methane when exposed to levels of ultraviolet radiation equivalent to sunlight falling on Mars' surface and varies seasonally and by latitude (matching the observed methane). As Mars experiences a higher rate of meteorites landing on its surface, the scientists provide a non-biological explanation for much, if not most, of its detected methane (University of Edinburgh press release; and Keppler et al, 2012).
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.)
Mars once may have had an atmosphere as dense as Earth's. On November 21, 2008, however, researchers announced new evidence that the atmosphere of Mars was and is still being stripped away by the Solar Wind. Although Mars has a weak magnetic field, it is very much unlike Earth's which is like a global bubble. The magnetic field around Mars is in the form of magnetic umbrellas that emanate from the Martian surface and and reach beyond the top of its atmosphere. Numbering in the dozens, these umbrellas about 40 percent of the planet’s surface, mainly in the southern hemisphere. These umbrella fields can link with the magnetic field in the Solar Wind through "magnetic reconnections" so that the joined fields wrapped themselves around a packet of gas at the top of the Martian atmosphere to form a magnetic capsule a thousand kilometers wide with ionized air trapped inside. Subsequently, the pressure of the Solar Wind pressure can "pinch off" the capsule (or "plasmoid") and blow its load of air away into deep space (more).
A great ocean once covered slightly over a third of the Martian surface some 3.5 billion years ago, according to a new study by scientists at the University of Colorado in Boulder (CU-Boulder). Although previous studies had proposed the existence of a large, ancient ocean on Mars over the past two decades, the available evidence was repeatedly contested. This new study provides further support for the idea of a sustained sea on the Red Planet within and along the margins of the northern lowlands during Mars' wet and warm Noachan epoch (around 4.1 billion to 3.7 billion years ago), based on global databases of known river delta deposits, valley networks, and present-day Martian topography. In a related study, scientists also detected roughly 40,000 river valleys on Mars, around four times the number of river valleys previously identified. These new findings also support the hypothesis that an ocean formed on early Mars as part of a global and active hydrosphere. The ancient ocean likely covered about 36 percent of the planet and contained around 30 million cubic miles, or 124 million cubic kilometers, of water -- the equivalent of a 1,800-foot, or 550-meter-deep layer of water spread out over the entire planet, but still about 10 times less than the current volume of Earth's oceans (CU-Boulder press releases of June 13, 2010; June 17, 2009; and Di Achille and Hynek, 2010). The finding of glacial moraines in Mars' northern highlands and the recent failure to detect significant deposits of phyllosilicate minerals in presumed northern ocean sediments from orbiting probes, however, indicate that his ancient ocean, was cold and surrounded by glaciers (Fairén et al, 2011; Bob Yirka, PhysOrg.com, August 29, 2011; and Jason Major, Universe Today, August 31, 2011).
Signs of Life?
On September 3, 2010, scientists working on data and experiments prompted by the findings of the 2008 NASA Phoenix Lander announced that soil examined by NASA's two Viking landers in 1976 may have contained "carbon-based chemical building blocks of life" (commonly called "organic compounds") (NASA news release; and Navarro-Gonalez et al, 2010). The Viking landers had heated Martian soil samples and detected the organic compounds chloromethane (methyl chloride or CH3Cl) and dichloromethane (methylene chloride, methylene dichloride, or CH2Cl2), but these chlorine compounds were interpreted at the time as likely contaminants from cleaning fluids used on Earth. Since 2008, however, scientists have determined that those chemical compounds are also detected when a little perchlorate (ions of salts containing chlorine and oxygen which were found in the Martian Arctic's ice-rich soil by Phoenix, but which would have destroyed many organic compounds in chemical reactions when heated) was added to what is believed to be the Earth's most comparable soil from the dry, cold, and often salty Atacama Desert in Chile containing trace organics and perchlorates and analyzed in the manner of the Viking tests.
Larger image of Martian terrain
overlaid by frost at the Viking 2
landing site in Utopia Planitia
of Mars' southern highlands at
the antipode of Argyre, which is
one of the Red Planet's largest,
recognizable impact regions.
New experiments informed by the
2008 Phoenix Lander indicate that
the two 1976 Viking landers may
have found organic compounds
on the Red Planet (more).
On August 6, 2009, scientists studying and modelling observed variations in Martian methane emissions announced that the gas was being produced and destroyed much faster on Mars than can be explained with known Earth processes (Mars Express news Release; Jessica Griggs, News Scientist, August 5, 2009; Judith Burns, BBC News, August 5, 2009; and Lefèvre and Forget, Nature, 2009).
© 2009 Nature Publishing Group,
Lefèvre and Forget, 2009
Martian atmospheric methane
is being produced and destroyed
faster than would be expected
from known Earth processes (more).
On January 15, 2009, a team of scientists (including Michael Mumma, Geronimo Villanueva, Robert Novak, Tilak Hewagama, Boncho Bonev, Michael Disanti, Avi Mandell, and Michael Smith) announced the confirmation of three hot spots of repeated methane emissions north of the Martian equator during local summers (NASA press release; Science@NASA; Mumma et al, 2009; Rachel Courtland, New Scientist, January 15, 2009; and Marc Kaufman, Washington Post, January 16, 2009). Detected by three scientific teams since 2003, methane plumes were vented from areas exhibiting evidence of ancient ground ice or flowing water (at a rift called Nili Fossae, a flat cratered region in the large upland region of Arabia Terra known as Terra Sabae, and the southeastern region of Syrtis Major, an ancient volcano about 745 miles or 1,200 kilometers across). They were unable to resolve from the methane emissions and other data whether Mars is either biologically or geologically active. If Martian microbes are producing the methane, however, they may reside far below the surface where it can be warm enough for liquid water to exist. On Earth, bacteria have been found some 1.2 to 1.9 miles (1.9 to 3.1 km) beneath the Witwatersrand basin of South Africa, where natural radioactivity breaks down water molecules into oxygen and hydrogen, which can be used biologically for energy. On the other hand, on Earth, the conversion of iron oxide into the serpentine group of minerals can also create methane, and on Mars this process would use water, carbon dioxide, and the planet's internal heat (more discussion of methane detections below under 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).
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, email@example.com, February 25, 2005).
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
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 firstname.lastname@example.org 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).
Beginning with the 1976 NASA Viking mission, Martian landers have found a planetary surface covered with rocks that are coated with a dark and reflective sheen. On Earth, there also regions with many rocks that have a similarly looking, reflective dark brown-to-black sheen called "rock" or "desert varnish," typically in arid and semi-arid climates. This coating is mainly composed of fine-grained, clay particles (around 70 percent) that bind iron and manganese oxides (around 30 percent) to create a mirror-like sheen. The coating has been found to to be very slow-growing and very thin, typically just 1 to 2 micrometers thick and apparently taking as more than a thousand years to grow in many arid areas. Recent research has supported the hypothesis that microbial colonies on the surface of the rocks create the varnish. In the extremely arid Yungay region of the Atacama Desert, along the Pacific Coast of South America, genetic analysis of rock varnish have found a diverse microbial community ranging from cyanobacteria to a-proteobacteria. The extraction of DNA from rock varnish collected at Yungay, where little to no DNA has been found in the surface soil to date, indicates that rock varnish may provide a niche habitat for microbial life where water is essentially absent. The findings also show that only a few micrometers of varnish material are enough to shelter microbes like Chroococcidiopsis spp. from the intense ultraviolet radiation present in the Atacama Desert (Barry E. DiGregorio, New Scientist, February 10, 2010; RedOrbit post, December 17, 2008; and Kuhlman et al, 2008).
Signs of Ancient Life?
At a late April 2010, Nasa-sponsored conference on Astrobiology, a NASA Mars Meteorite Research Team presented new evidence supporting its 1996 assertion that a 4-billion-year-old meteorite from Mars which landed thousands of years ago on Antarctica shows evidence of microscopic life on Mars. In addition to new evidence disproving counter-claims of non-biological origins for the "biomorphs" in meteorite ALH84001 (which may be mini-fossils of single-celled organisms or pits and textures formed by long-gone bacteria colonies), the team reported that additional Martian meteorites appear to house distinct and identifiable microbial fossils that point even more strongly to the past existence of life on Mars (Marc Kaufman, Washington Post, May 4, 2010; and NASA Johnson Space Center news release of November 25, 2009, with additional images and links to papers; "Life on Mars Hypothesis" presentation; Mckay et al, 2009; and Thomas-Keprta et al, 2009).
Mars Meteorite Research Team,
Possible "biomorph" (mini-fossil
of a single-celled organism or
pits and textures formed by
long-gone bacteria colonies) in
a Martian meteorite found on
On April 16, 2010, a group of scientists published a paper providing a younger age estimate of 4.091 ± 0.030 billion years old for the famous Martian meteorite (ALH84001) based on analysis isotope of elements Lutetium (Lu) and Hafnium (Hf). The alternative age estimate is around 400 million years younger than dating using Samarium (Sa) and Neodymium (Nd) isotopes. It would place the ejection of the meteorite from Mars after a time when the inner Solar System's heavy meteoric bombardment but before Martian core's internal magnetic dynamo had stopped. The findings suggests that that ALH84001 was formed after a period of intense volcanic activity, when Mars was "wet" and had a stable magnetic field, environmental conditions that could have fostered the development of simple life (Lewis Brindley, Chemistry World, April 15, 2010; and Lapen et al, 2010).
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).
Possible fossil Martian nanobacteria
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.
In June 2009, planetary scientists published a paper that rejected two non-biological hypotheses (involving carbonate decomposition under high pressure and temperature) proposed for the creation of nanocrystal magnetites found in Martian meteorite ALH84001 that appears to provide evidence of ancient Martian microbial life (Hannah Devlin, Times Online, November 27, 2009; Robert Fisher, New Scientist, November 27, 2009; Thomas-Kerpta et al, 2009; Alan H. Treiman, 2004; and Adrian L. Brearley, 2003). In August 2009, planetary scientists provided evidence that three minerals (including calcium, magnesium, and iron) found in the meteorite were formed in balmy waters (less than 100 °C or 212 °F) that would have been conducive to life (David Shiga, New Scientist, August 28, 2009; and Boynton et al, 2009). The new analyses indicate that the rock came from a site on Mars where the environment had conditions friendly to Earth-type life.
Try the NASA Astrobiology Institute (NAI).
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