Searching For Early Life On Mars
June 12, 2010 3 Comments
Mars our neighboring planet, similar in environment to Earth, has ever been suggested as best candidate for our future colonization. The recent findings and data sent from Mars Phoenix Lander, suggested there was water in early mars.
Laboratory tests aboard NASA’s Phoenix Mars Lander have identified water in a soil sample. The lander’s robotic arm delivered the sample Wednesday to an instrument that identifies vapors produced by the heating of samples.The soil sample came from a trench approximately 2 inches deep. When the robotic arm first reached that depth, it hit a hard layer of frozen soil. Two attempts to deliver samples of icy soil on days when fresh material was exposed were foiled when the samples became stuck inside the scoop. Most of the material in Wednesday’s sample had been exposed to the air for two days, letting some of the water in the sample vaporize away and making the soil easier to handle.Besides confirming the 2002 finding from orbit of water ice near the surface and deciphering the newly observed stickiness, the science team is trying to determine whether the water ice ever thaws enough to be available for biology and if carbon-containing chemicals and other raw materials for life are present.[Source: NASA]
Rocks examined by NASA’s Spirit Mars Rover hold evidence of a wet, non-acidic ancient environment that may have been favorable for life. Confirming this mineral clue took four years of analysis by several scientists. An outcrop that Spirit examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic. NASA’s rovers have found other evidence of formerly wet Martian environments. However the data for those environments indicate conditions that may have been acidic. In other cases, the conditions were definitely acidic, and therefore less favorable as habitats for life. Laboratory tests helped confirm the carbonate identification. The findings were published online Thursday, June 3 by the journal Science.[Source: NASA]
Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere.
It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.
Most of our universe appears to be a hostile place for life to exist with no planetary bodies except Earth harboring life as we know it. However, similar notions were previously thought of Earth’s extreme environments such as acidic hot springs, deepsea vents or solar salterns, which were believed to be too “extreme” to nurture life. Yet numerous studies over the last decades have shown that these extreme environments actually harbor an incredible diversity of Eukarya, Bacteria and Archaea. The very same may hold true for the search for extraterrestrial life: Just because we have not found it yet, does not mean it cannot exist. However, there is still the question of what are we actually looking for, and where?
The most recent findings suggest that planet was warmer and wetter in the past. What tend to evolution of life on Earth is warmer environment and water. With this assumption in mind, Mars is probably our best chance to find life, extant or extinct, within our Solar System and recent results from the Phoenix Mars Lander have actually shown evidence for water in modern day Martian soil. Another intriguing find was made by the Mars Rovers Spirit and Opportunity, when they discovered halite and sulfate evaporated rocks on Mars. This suggests that hypersaline brine pools may have been relatively common on the surface of Mars, which in turn may have been a suitable environment for a family of Archaea which thrive on Earth: the family Halobacteriaceae. On Earth, modern hypersaline brine pools are not solely inhabited by halophilic Archaea. Two examples of other inhabitants are Salinibacter ruber or the unicellular green algae Dunaliella salina. In the search of extraterrestrial life, halophilic Archaea are of particular interest as they are amazingly robust organisms, able to survive being desiccated into a crust of solid salt. Sealed in such salt crystals, halophiles have an extremely high, and perhaps indefinite, longevity. Interestingly, these halophilic Archaea are not known to form spores, thus it is of great interest how they can survive for an extended period of time. Ancient stromatolites date as far back as 3.5 billion years and may have provided the first micro-environments on early Earth, as they were fashioned in ancient oceans, which may have been 6% NaCl.
Not only is there the suggested relative common occurrence of hypersaline environments on Mars in its early history, but one can also imagine that any simple microorganisms could interact in some way with their physical environment to form similar “Earth-like” mats or stromatolites. Thus it is not unthinkable if life were to exist on early Mars that stromatolites were a common occurrence in the past, and which may have harbored halophilic Archaea. Once water on Mars started to evaporate, forcing any stromatolites to become extinct, halophilic Archaea may have become entrapped in halite where they continued to flourish. Halophilic Archaea may survive for millions of years enclosed in salt crystals. This makes them prime candidates for organisms that may have been present on early Mars and raises the possibility that even nowadays, they may be enclosed and dormant, trapped in a crystal.[Ref: Microbial Life Educational Resources]
As the crystals grow, small pockets of brine are trapped within the salt structure. As the rate of crystal growth increases, the quantity of fluid inclusions also increases. Quantities of inclusions are greatest in the center of the crystal (Roedder, 1984). As a crystal forms, sometimes halophiles become trapped within the fluid inclusion of the halite crystals. These enclosed halophiles may remain viable in the inclusions for many years (Norton and Grant, 1988; Norton et al., 1993; Denner et al., 1994; Grant et al., 1998; Vreeland et al., 2000). The population of viable halophiles is hypothesized to decrease as resources are depleted over time (Norton and Grant, 1988).
Various species of halophilic Archaea (halophiles) have been revived from fluid inclusions in ancient salt crystals (Norton et al., 1993; Denner et al., 1994; Grant et al., 1998; Vreeland et al., 2000). A new species, Halococcus salifodinae, was one novel isolate discovered in an Austrian salt mine (Denner et al., 1994). Many different species were isolated from salt crystals in two British salt mines. Based on lipid patterns, three out of nine taxonomic groups of halophiles were isolated from both of the salt mines (Norton et al., 1993).
The principal morphological types of these haloarchaea are rods, cocci and irregular pleomorphic forms. Halophilic Archaea thrive even in concentration of salt five times greater than the salt concentration of the ocean and in salt concentrations higher than those used in any food pickling processes. They in fact require salt for growth and they are adapted to environments which have little or no oxygen available for respiration. Instead, their cellular machinery contains charged amino acids on their surfaces, which react to the salt. The proteins of halophilic Archaea are highly adapted and engineered to function in their natural environment, which usually contains between 2 and 5 M inorganic salts. Another interesting feature is that the genomic structures of these organisms have adapted to lower the occurrence of potential lesions induced by the natural occurring high UV radiation within their environment and thus no ozone is required to ensure their survival.
Halophilic Archaea have been found in two habitats, stromatolites and halite crystals, which have important implications for their ability to also thrive in extra-terrestrial environments. Ancient stromatolites may offer clues to the evolution of life on Earth, and possibly Mars, as they have been present on Earth for 3.5 billion years and may have been one of the first microenvironments to harbor early life. At this point, it needs to be acknowledged that the biological origin of ancient stromatolites is still controversial with opinions divided between diverse inorganic or biosedimentary origins. Nevertheless, it is reasonable to assume that at least some ancient stromatolites have been formed due to biosedimentation. The microbial ecosystem on the top layer of the stromatolite plays the role of a filter that enhances, inhibits or passively allows the growth process. Thus, the formation of stromatolites results from interactions and balance between intrinsic (microbial mat and biofilm) and extrinsic factors (environmental conditions). Many important steps of evolution may have also occurred within stromatolites owing to the close proximity of diverse microorganisms and microniches.
[Image Credit: http://astrobiology.nasa.gov%5D
How to detect such Halophiles? Well, microbial life, if extinct or extant on Mars, would produce biomolecules that might be preserved and detectable in Martian rocks. A biomarker is a specific cell constituent produced by microorganisms and when detected, conclusively shows that living organisms are or were present in the environment. Examples of biomarkers are lipids, steroids, and pigments. Halophilic Archaea are mostly pigmented red due to a high content of C50 carotenoid pigments (α- bacterioruberin and derivates) in their membranes. Recent studies have shown, that these pigments can be detected by Resonance Raman spectroscopy which is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.
The past decade has seen a rapid increase in technology and possibilities to look for life on different planets. Further mission to Mars will undoubtedly increase or understanding of the history of the red planet and probably offer insights into our own evolution. With all the evidence pointing at the moment to a warm and wet early Martian environment, it may be conceivable that life was thriving in a hypersaline ancient ocean on early Mars. Similar to the modern day environment of Shark Bay, stromatolites may have been present at the time, harboring and sheltering life. Once the environment was changing, in particular the loss of water, organisms may have been entrapped within forming salt crystals. Those crystals containing halophilic Archaea perhaps may still be lying dormant beneath the Martian surface, waiting for us to find them.
Implications The presence of Halophiles on Mars would certainly boost the possibility of other algae like that. In my early post “How Close We Are to Colonize Galaxy?” a commenter and regular reader of this site Nelson, points out that presence of petroleum on Mars could help us in colonization of Mars in several way. I’m amazed can’t we find petroleum if there is extinct algae on Mars?Sure, we could.