An “habitable” lake in Mars 3800 million years ago
As I mentioned in this blog a year and a half before (August 30th, 2012 “Is there life on Mars?”), the Curiosity rover began to walk by Mars, specifically inside the Gale crater, carrying its sophisticated instruments to analyze rocks, soil and atmosphere, that is, a well equipped geochemical laboratory analyzing the surface of another planet for the first time. You can see a video of 2 minutes of the 1st year of Curiosity here. As you know, one of the objectives of this analysis is to find evidence of whether there were favorable conditions for life on Mars, albeit in very bygone eras.
The Curiosity rover is walking inside Gale Crater, east of Syrtis Major, the Mars most prominence visible through a telescope. Image NASA/ESA/Hubble.
Mars is a planet with some similar features on Earth, such as the length of day, slightly more than 24 hours, but the greater distance from the Sun and very tenuous atmosphere make the average temperature to be -63 ° C, with daily oscillations from +20°C to -140°C. Having no oceans, the land surface of Mars is equivalent to the Earth, because Mars is smaller.
Comparison of Earth and Mars. The diameter of Mars is 3400 km, approx half of the Earth’s, but excluding oceans, the solid surface is similar on both planets. Image taken from T.E. Harrison, New Mexico State University.
Despite the difficulties to demonstrate the current existence of liquid water on Mars, from some years ago evidences have been found that there was water in the Martian surface, and it is being confirmed that during the first thousand million years there was plenty of water on Mars (Remind that both Mars and Earth are about 4.5 billion years).
Appearance of a region of Mars indicating the flow of water in the distant past. Image taken from T.E. Harrison, New Mexico State University.
Water history in Mars, in billions of years. Image from T.E. Harrison, New Mexico State University.
Curiosity shows an “habitable” lake 3800 million years ago
Thus, Curiosity rover has been taking samples in various ways (see in Figure below the 5 cm holes taking samples) and analyzing them. Studying the data, scientists have been able to write a series of articles that have been published in Science and other prestigious journals.
Two 5 cm holes made by Curiosity rover sampling in Yellowknife Bay of Gale Crater on Mars (NASA/JPL-Caltech/MSSS)
Among other articles, by last May was already published one (Williams et al 2013) with observations that the material extracted from the Yellowknife Bay of Gale Crater shows textures typical of fluvial sedimentary conglomerates, with rounded pebbles that indicate fluvial abrasion, and by their characteristics a water flow of nearly 1 meter per second has been deduced, with a depth of near 1 meter. Therefore, when this area was formed the climatic conditions, with abundant rivers, would have been very different from the current hyperarid and very cold environment.
A few weeks ago, on December 9th, Science Online has released a special edition dedicated to the latest findings of Curiosity, with 6 articles asserting that at Gale Crater there would have been a lake theoretically habitable for some organisms.
In one of the articles, maybe the most relevant one, Grotzinger et al (2013) describe the sedimentary rocks found by the rover and demonstrate that it corresponded to an aqueous environment with neutral pH, low salinity and different redox states of Fe and S. The presence of C, H, O, S, N and P (i.e., all biogenic elements) is also shown, and the authors estimate that this favorable environment for life could have lasted some few hundred thousand years, and therefore it demonstrates the biological feasibility of this fluvio-lacustrine environment of post-Noachian Mars, that is, about 3800 million years ago.
Therefore, these scientists deduced that this lake had fresh water, a water we could drink, and that around this lake various fluvial and lacustrine environments were present. This environment should be habitable for some organisms, and very similar to some current earth environments. The commented chemical compounds would be suitable for the survival of bacteria chemolithotrophic bacteria, id est, those which use inorganic compounds (such as Fe or S) as an energy source and use CO2 as a carbon source. On Earth we have many kind of these microbes, such as iron bacteria (Thiobacillus) or sulfur bacteria (including some sulfur thermophilic archaea) and the nitrifying ones. Although most of these chemolithotrophic bacteria on Earth are aerobic because they use atmospheric oxygen as electron acceptor, this metabolism is also known in some anaerobes, such as those that do the anoxic ammonium oxidation (process “Anammox”), for example Brocadia anammoxidans, or the same nitrifying bacteria in anaerobic conditions.
Therefore, with this habitable lake for some time, and with other similar environments, we can not reject the possibility that living beings had been sometimes in Mars.
View from Yellowknife Bay in Gale Crater, looking W-NW. This area of sedimentary deposits was the bottom of a freshwater lake. Photo: NASA/JPL-Caltech.
Estimated size and shape of the lake that was in the Gale crater. There must have been other similar. The arrows indicate the direction of the alluvial fan that flowed into the crater from its wall. Photo: NASA/JPL-Caltech/MSSS.
Another aspect studied in this extra issue of Science is the possible presence of methane in the Martian atmosphere (Webster et al 2013). Just like on Earth, methane is a potential sign of biological activity in the past. Previous observations made from Earth or from the Mars orbit speculated on the presence of some 10 ppb of methane, and its subsurface biological origin was also discussed. Nevertheless, in the measurements made in situ by laser spectrometry of Curiosity rover using a specific spectral methane pattern, it has not been detected since the values found are lower than 1 ppb. This reduces the probability of recent methanogenic microbial activity on Mars and it is limiting the possible contribution of recent geological and extraplanetary sources.
Finally, in another article (Hassler et al 2013) about measures of cosmic rays on the surface of Mars that Curiosity has made over a year, models of radiation are elaborated, for the time calculation of possible subsurface microbial survival, and also for the preservation of organic compounds of biological origin finding them billions of years later. Unfortunately, the conclusion is that the powerful effect of cosmic rays would cause very difficult any of these possibilities. Unlike the Earth, the magnetic field of Mars is very weak and the atmosphere too, things that help bombardment of cosmic rays and the solar wind on the Martian surface. However, there is evidence that in the past Mars had a magnetic field more effective, so hope is not lost …..
Achenbach J. 2013. NASA Curiosity rover discovers evidence of freshwater Mars lake. The Washington Post, Health & Science online Dec 9.
Anderson PS. 2013. Curiosity rover confirms ancient martian lake. Spaceflight Insider online Dec 11.
Grotzinger JP et 72 al. 2013. A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars. Science DOI: 10.1126/science.1242777 online Dec 9, 2013.
Harrison, T.E., New Mexico State University: http://astronomy.nmsu.edu/tharriso/ast105/Mars.html
Hassler DM et 23 al. 2013. Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover. Science DOI: 10.1126/science.1244797 online Dec 9, 2013.
Kerr, RA. 2013. New Results Send Mars Rover on a Quest for Ancient Life. Science Now News, online Dec 9, 2013.
Science Special Collection Curiosity 2013. Curiosity at Yellowknife Bay, Gale Crater. Online: http://www.sciencemag.org/site/extra/curiosity/
Webster CR et al 2013. Low upper limit to methane abundance on Mars. Science 18 October 2013, Vol. 342 no. 6156 pp. 355-357
Williams RME et 38 al. 2013. Martian Fluvial Conglomerates at Gale Crater. Science 31 May 2013, Vol. 340 no. 6136 pp. 1068-1072