Artist's impression of Mars during the Noachian Era. Credit: Ittiz/Wikipedia Commons
Ever since robotic explorers began visiting the Red Planet during the 1960s and 70s, scientists have puzzled over Mars’ surface features. These included flow channels, valleys, lakebeds, and deltas that appear to have formed in the presence of water. Since then, dozens of missions have been sent to Mars to explore its atmosphere, surface, and climate to learn more about its warmer, wetter past. In particular, scientists want to know how long water flowed on the surface of Mars and whether it was persistent or periodic in nature.
The ultimate purpose here is to determine whether rivers, streams, and standing bodies of water existed long enough for life to emerge. So far, missions like Curiosityand Perseverancehave gathered volumes of evidence that show how hundreds of large lakebeds once dotted the Martian landscape. But according to a new study by an international team of researchers, our current estimates of Mars’ surface water may be a dramatic understatement. Based on a meta-analysis of years’ worth of satellite data, the team argues that ancient lakes may have once been a very common feature on Mars.
Artist's impression of Mars during the Noachian Era. Credit: Ittiz/Wikipedia Commons
Billions of years ago, Mars was a much different place than it is today. During the same period when life was first emerging on Earth, Mars had a thicker atmosphere, warmer surface temperatures, and flowing water on its surface. Evidence of this warmer, wetter past is preserved on the planet’s surface today in the form of river channels, lakebeds, alluvial fans, and sedimentary deposits. When this period began, and how long it lasted, remains the subject of much debate for scientists.
Knowing how long this period lasted helps establish how big the window of opportunity was for life on Mars. But according to new NASA-funded research from the Sellers Exoplanet Environments Collaboration (SEEC), Mars may have been wetter longer than previously expected. According to recently published results in the Proceedings of the National Academy of Sciences, Mars may have had a northern ocean as recent as three billion years ago.
Artist's impression of Mars during the Noachian Era. Credit: Ittiz/Wikipedia Commons
All across the Martian surface, there are preserved features that tell the story of what Mars once looked like. These include channels that were carved by flowing water, delta fans where water deposited sediment over time, and lakebeds where clay and hydrated minerals are found. In addition to telling us more about Mars’ past, the study of these features can tell us about how Mars made the transition to what it is today.
According to new research led by Brown Ph.D. student Ben Boatwright, an unnamed Martian crater in Mars southern highlands showed features that indicate the presence of water, but there is no indication of how it got there. Along with Brown professor Jim Head (his advisor), they concluded that the crater’s features are likely the result of runoff from a Martian glacier that once occupied the area.
In this image, we can see a small notch in a crater rim with a well-formed channel. Lava appears to have flowed through this notch and filled in this approximately 10-kilometer diameter crater. Image Credit: NASA/JPL/UArizona
At a fundamental level, Mars is a volcanic planet. Its surface is home to the Solar System’s largest extinct volcano, Olympus Mons, and another trio of well-known volcanoes at Tharsis Montes. And those are just the highlights: there are many other volcanoes on the surface. Though that volcanic activity ceased long ago, the planet’s surface tells the tale of a world disrupted and shaped by powerful volcanic eruptions.
A vertically exaggerated, false-color view of a large, water-carved channel on Mars called Dao Vallis. Image: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO. 3D rendered and colored by Lujendra Ojha
For decades, robotic missions have been exploring Mars to learn more about the planet’s geological and environmental history. Next year, the Perseverance rover will join in the hunt and be the first mission to send samples back to Earth and by the 2030s, the first crewed mission is expected to take place. All of these efforts are part of an ongoing effort to find evidence of past (and maybe even present) life on Mars.
According to a new study from Rutgers University-New Brunswick., the most likely place to find this evidence is located several kilometers beneath the surface. It is here (they argue) that water still exists in liquid form, which is likely the result of geothermal heating melting thick subsurface sheets of ice. This research could help resolve lingering questions like the faint young Sun paradox.
Future missions could determine the presence of past life on Mars by looking for signs of extreme metal-metabolizing bacteria. Credit: NASA.
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.
Metallosphaera sedula grown on synthetic Martian Regolith. The microbes are specifically stained by Fluorescence-In-Situ-Hybridization (FISH). Credit: Tetyana Milojevic
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.”
Microspheroids containing mostly aluminium and chlorine overgrow the mineral surface of synthetic Mars regolith. These microspheroids can only be observed after cultivation of Metallosphaera sedula Credit: Tetyana Milojevic
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.
