NASA and the China National Space Agency (CNSA) plan to mount the first crewed missions to Mars in the next decade. These will commence with a crew launching in 2033, with follow-up missions launching every 26 months to coincide with Mars and Earth being at the closest point in their orbits. These missions will culminate with the creation of outposts that future astronauts will use, possibly leading to permanent habitats. In recent decades, NASA has conducted design studies and competitions (like the 3D-Printed Habitat Challenge) to investigate possible designs and construction methods.
For instance, in the Mars Design Reference Architecture 5.0, NASA describes a “commuter” architecture based on a “centrally located, monolithic habitat” of lightweight inflatable habitats. However, a new proposal envisions the creation of a base using organisms that extract metals from sand and rock (a process known as biomineralization). Rather than hauling construction materials or prefabricated modules aboard a spaceship, astronauts bound for Mars could bring synthetic bacteria cultures that would allow them to grow their habitats from the Red Planet itself.
When it comes time to begin conducting regular crewed missions to Mars, and perhaps even establishing a permanent outpost there, astronauts and potential Martian settlers will have to know how to work with the local environment. Remember that scene in The Martian where astronaut Mark Whatney (Matt Damon) is forced to grow his own food in a plot of Martian soil? Well, it will be much like that, except with a lot more mouths to feed.
Naturally, knowing if this can be done requires a great deal of research and experimentation. To assist these efforts, a team of astrophysicists from the University of Central Florida (UCF) recently developed a scientifically based, standardized method for creating Martian and asteroid soil simulants. This imitation Martian dirt, which goes for $20 a kilogram (about $10 a pound), will help researchers determine what it takes to grow crops on the Red Planet.
Mars is not exactly a friendly place for life as we know it. While temperatures at the equator can reach as high as a balmy 35 °C (95 °F) in the summer at midday, the average temperature on the surface is -63 °C (-82 °F), and can reach as low as -143 °C (-226 °F) during winter in the polar regions. Its atmospheric pressure is about one-half of one percent of Earth’s, and the surface is exposed to a considerable amount of radiation.
Until now, no one was certain if microorganisms could survive in this extreme environment. But thanks to a new study by a team of researchers from the Lomonosov Moscow State University (LMSU), we may now be able to place constraints on what kinds of conditions microorganisms can withstand. This study could therefore have significant implications in the hunt for life elsewhere in the Solar System, and maybe even beyond!
For the sake of their study, the research team hypothesized that temperature and pressure conditions would not be the mitigating factors, but rather radiation. As such, they conducted tests where microbial communities contained within simulated Martian regolith were then irradiated. The simulated regolith consisted of sedimentary rocks that contained permafrost, which were then subjected to low temperature and low pressure conditions.
As Vladimir S. Cheptsov, a post-graduate student at the Lomonosov MSU Department of Soil Biology and a co-author on the paper, explained in a LMSU press statement:
“We have studied the joint impact of a number of physical factors (gamma radiation, low pressure, low temperature) on the microbial communities within ancient Arctic permafrost. We also studied a unique nature-made object—the ancient permafrost that has not melted for about 2 million years. In a nutshell, we have conducted a simulation experiment that covered the conditions of cryo-conservation in Martian regolith. It is also important that in this paper, we studied the effect of high doses (100 kGy) of gamma radiation on prokaryotes’ vitality, while in previous studies no living prokaryotes were ever found after doses higher than 80 kGy.”
To simulate Martian conditions, the team used an original constant climate chamber, which maintained the low temperature and atmospheric pressure. They then exposed the microorganisms to varying levels of gamma radiation. What they found was that the microbial communities showed high resistance to the temperature and pressure conditions in the simulated Martian environment.
However, after they began irradiating the microbes, they noticed several differences between the irradiated sample and the control sample. Whereas the total count of prokaryotic cells and the number of metabolically active bacterial cells remained consistent with control levels, the number of irradiated bacteria decreased by two orders of magnitude while the number of metabolically active cells of archaea also decreased threefold.
The team also noticed that within the exposed sample of permafrost, there was a high biodiversity of bacteria, and this bacteria underwent a significant structural change after it was irradiated. For instance, populations of actinobacteria like Arthrobacter – a common genus found in soil – were not present in the control samples, but became predominant in the bacterial communities that were exposed.
In short, these results indicated that microorganisms on Mars are more survivable than previously thought. In addition to being able to survive the cold temperatures and low atmospheric pressure, they are also capable of surviving the kinds of radiation conditions that are common on the surface. As Cheptsov explained:
“The results of the study indicate the possibility of prolonged cryo-conservation of viable microorganisms in the Martian regolith. The intensity of ionizing radiation on the surface of Mars is 0.05-0.076 Gy/year and decreases with depth. Taking into account the intensity of radiation in the Mars regolith, the data obtained makes it possible to assume that hypothetical Mars ecosystems could be conserved in an anabiotic state in the surface layer of regolith (protected from UV rays) for at least 1.3 million years, at a depth of two meters for no less than 3.3 million years, and at a depth of five meters for at least 20 million years. The data obtained can also be applied to assess the possibility of detecting viable microorganisms on other objects of the solar system and within small bodies in outer space.”
This study was significant for multiple reasons. On the one hand, the authors were able to prove for the first time that prokaryote bacteria can survive radiation does in excess of 80 kGy – something which was previously thought to be impossible. They also demonstrated that despite its tough conditions, microorganisms could still be alive on Mars today, preserved in its permafrost and soil.
The study also demonstrates the importance of considering both extraterrestrial and cosmic factors when considering where and under what conditions living organisms can survive. Last, but not least, this study has done something no previous study has, which is define the limits of radiation resistance for microorganisms on Mars – specifically within regolith and at various depths.
This information will be invaluable for future missions to Mars and other locations in the Solar System, and perhaps even with the study of exoplanets. Knowing the kind of conditions in which life will thrive will help us to determine where to look for signs of it. And when preparing missions to other words, it will also let scientists know what locations to avoid so that contamination of indigenous ecosystems can be prevented.
Today, there are multiple lines of evidence that indicate that during the Noachian period (ca. 4.1 to 3.7 billion years ago), microorganisms could have existed on the surface of Mars. These include evidence of past water flows, rivers and lakebeds, as well as atmospheric models that indicate that Mars once had a denser atmosphere. All of this adds up to Mars having once been a warmer and wetter place than it is today.
However, to date, no evidence has been found that life ever existed on Mars. As a result, scientists have been trying to determine how and where they should look for signs of past life. According to a new study by a team of European researchers, extreme lifeforms that are capable of metabolizing metals could have existed on Mars in the past. The “fingerprints” of their existence could be found by looking at samples of Mars’ red sands.
For the sake of their study, which recently appeared in the scientific journal Frontiers of Microbiology, the team created a “Mars Farm” to see how a form of extreme bacteria might fare in an ancient Martian environment. This environment was characterized by a comparatively thin atmosphere composed of mainly of carbon dioxide, as well as simulated samples of Martian regolith.
They then introduced a strain of bacteria known as Metallosphaera sedula, which thrives in hot, acidic environments. In fact, the bacteria’s optimal conditions are those where temperatures reach 347.1 K (74 °C; 165 °F) and pH levels are 2.0 (between lemon juice and vinegar). Such bacteria are classified as chemolithotrophs, which means that they are able to metabolize inogranic metals – like iron, sulfur and even uranium.
These stains of bacteria were then added to the samples of regolith that were designed to mimic conditions in different locations and historical periods on Mars. First, there was sample MRS07/22, which consisted of a highly-porous type of rock that is rich in silicates and iron compounds. This sample simulated the kinds of sediments found on the surface of Mars.
Then there was P-MRS, a sample that was rich in hydrated minerals, and the sulfate-rich S-MRS sample, which mimic Martian regolith that was created under acidic conditions. Lastly, there was the sample of JSC 1A, which was largely composed of the volcanic rock known as palagonite. With these samples, the team was able to see exactly how the presence of extreme bacteria would leave biosignatures that could be found today.
As Tetyana Milojevic – an Elise Richter Fellow with the Extremophiles Group at the University of Vienna and a co-author on the paper – explained in a University of Vienna press release:
“We were able to show that due to its metal oxidizing metabolic activity, when given an access to these Martian regolith simulants, M. sedula actively colonizes them, releases soluble metal ions into the leachate solution and alters their mineral surface leaving behind specific signatures of life, a ‘fingerprint’, so to say.”
The team then examined the samples of regolith to see if they had undergone any bioprocessing, which was possible thanks to the assistance of Veronika Somoza – a chemist from the University of Vienna’s Department of Physiological Chemistry and a co-author on the study. Using an electron microscope, combined with analytical spectroscopy technique, the team sought to determine if metals with the samples had been consumed.
In the end, the sets of microbiological and mineralogical data they obtained showed signs of free soluble metals, which indicated that the bacteria had effectively colonized the regolith samples and metabolized some of the metallic minerals within. As Milojevic indicated:
“The obtained results expand our knowledge of biogeochemical processes of possible life beyond Earth, and provide specific indications for detection of biosignatures on extraterrestrial material – a step further to prove potential extra-terrestrial life.”
In effect, this means that extreme bacteria could have existed on Mars billions of years ago. And thanks to the state of Mars today – with its thin atmosphere and lack of precipitation – the biosignatures they left behind (i.e. traces of free soluble metals) could be preserved within Martian regolith. These biosignatures could therefore be detected by upcoming sample-return missions, such as the Mars 2020 rover.
In addition to pointing the way towards possible indications of past life on Mars, this study is also significant as far as the hunt for life on other planets and star systems is concerned. In the future, when we are able to study extra-solar planets directly, scientists will likely be looking for signs of biominerals. Among other things, these “fingerprints” would be a powerful indicator of the existence of extra-terrestrial life (past or present).
Studies of extreme lifeforms and the role they play in the geological history of Mars and other planets is also helpful in advancing our understanding of how life emerged in the early Solar System. On Earth too, extreme bacteria played an important role in turning the primordial Earth into a habitable environment, and play an important role in geological processes today.
Last, but not least, studies of this nature could also pave the way for biomining, a technique where strains of bacteria extract metals from ores. Such a process could be used for the sake of space exploration and resource exploitation, where colonies of bacteria are sent out to mine asteroids, meteors and other celestial bodies.