When searching for signs of ancient life on Mars, NASA scientists increasingly focus on organic material — the carbon-based compounds that are the building blocks of life. Organics were found by the Curiosity rover in Gale Crater, and now new papers report they have also been identified by the instruments of the Perseverance rover in very different kinds of rock in Jezero Crater.
Unlike the Gale Crater organics that were found in sedimentary rocks, these newly found specimens are in igneous rocks — formed when molten rock cools and crystallizes — and are mixed with other compounds known to preserve organics well.
These rock samples are part of the NASA and European Space Agency Mars Sample Return mission, and so they could be brought to Earth in the future for more intensive study. Scientists are excited about what might some day be found.
The new findings about organics and the geology of Jezero Crater are part of a trio of articles in the journal Science published Wednesday.
The lead author of one of the papers, Michael Tice of Texas A&M University, gave this overview of what the Perseverance team is reporting:
“These three papers show that samples collected in the floor of Jezero should be able to tell us a lot about whether living organisms ever inhabited rocks under the surface of the crater over the past several billion years,” he wrote to me.
The paper he led, Tice said, shows that small amounts of water passed through those rocks at three different times, and that conditions at each of those times could have supported life. “Even more importantly, minerals were formed from the water that are known to be able to preserve organic matter and even fossils on Earth.”
Adding to the excitement over specific organics detections reported in the Science papers, the advanced instruments on Perseverance are allowing scientists to understand more clearly the presence of organics on Mars. The evolving picture is that they are widespread — in almost every rock according to one senior scientist.
Several dozen cores of Mars rocks, including those collected already and known to containing precious Martian organics, will be stored in metal tubes that are being left on the surface of Jezero. The diversity of rock samples collected so far has been sufficiently broad and intriguing that the first group of samples was cached last month at a Jezero site called Three Forks.
NASA and the European Space Agency are developing plans for their Sample Return Mission in the early 2030s, when those cannisters will picked-up and transport to Earth. Only back on Earth, in cutting-edge laboratories, will scientists be able to identify the organics in detail and learn about their origins.
Organic molecules consist of a wide variety of compounds that are always composed of carbon and usually including hydrogen and oxygen atoms. They can also contain other elements, such as nitrogen, phosphorus, and sulfur.
Organics are always present in anything living and certain molecules are considered potential biosignature – a substance or structure that could be evidence of past life.
But there are also many chemical processes that produce these molecules on Mars (and elsewhere) and organics are often present in meteorites and in space dust that lands on the Martian surface.
So finding organics is not the same as finding extraterrestrial life. Far from it. But still, it’s quite significant since, without organics, there could be no life, at least as we know it.
The first detections of organic on Mars came in 2014 from rock-powder samples drilled by the Curiosity rover in Gale Crater. The samples came from mudstone, a sedimentary rock associated with once-standing water.
Perseverance has detected organics several times, but the discoveries described in two of the Science papers released last week show something else of importance. These samples, which were drilled from igneous rock, also contain many sulfate minerals, which are known to preserve organics well and are important as a result.
In addition, they come from an area where, in the distant past, volcanic magma came into contact with water; in fact, it happened numerous distinct times. The result was widespread alterations or the magma-turned-ingenous rocks during this aqueous phases, and the formation or modification of organics and minerals.
That environment, Perseverance scientists report, had once been created there where life — if it existed — could have survived.
Perseverance is NASA’s most advanced rover yet, and can study Martian rocks in greater detail than any predecessor. Its suite of instruments includes Mastcam-Z, the “eyes” of the rover that allow it to study rocks at a distance, and two pieces of technology that perform X-ray and ultraviolet spectroscopy, which analyze in detail the make-up of rocks and minerals.
The two instruments able to do unprecedented spectroscopy on Mars are the SHERLOC instrument (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals), which uses deep-ultraviolet fluorescence and Raman spectrometer to map organic and mineral composition with a high precision, and PIXL (the Planetary Instrument for X-ray Lithochemistry.) PIXL can identify the elemental chemical composition using X-ray fluorescence, and it can identify features as small as a grain of salt.
It was PIXL that found the initial proof that Perseverance had landed on igneous rock. This was something of a surprise because Jezero contains a large fossil delta — which normally would feature sedimentary rock. The igneous rock came in several layers, the top Séítah formation and the base Máaz formation. Some rocks and outcrops from Máaz formation were on the surface and so could be sampled.
Igneous rocks are excellent timekeepers because crystals within them record details about the precise moment they formed. Those details in turn will tell scientists when the lake at Jezero was present and when the area was potentially most habitable.
The SHERLOC instrument was largely responsible for the lead Perseverance article in Science, which reported on organics found at three Jezero locations.
Bethany Ehlmann, co-author of the Science paper, and a professor of planetary science at the California Institute of Technology, said that the microscopic imaging capabilities of SHERLOC “have really blown open our ability to decipher the time-ordering of Mars’s past environments.”
“The microscopic fingerprints show igneous rocks formed and then water circulated through them, altering the rocks and depositing minerals in voids and cracks. In some places, data show evidence for organics within these potentially habitable niches.”
The Science paper’s lead author, Eva Scheller of MIT, said that only a small portion of the material collected so far has actually been studied spectroscopically, meaning that many more findings are likely coming.
She said that the organics identified so far are almost certainly not of biological origin, based on the information collected about them using the suite of Perseverance instruments.
The paper lead-authored by Michael Tice relied on both SHERLOC and PIXL data and also wrote of various non-biological ways that the organics could have been formed.
But the paper also adds that “it is not implausible” that some of the organic material detected in the Séítah formation and associated with sulfate salts “may reflect in situ production by chemoautotrophic/chemolithotrophic subsurface communities present during this second stage of rock alteration, potentially with subsequent alteration of the organic material itself.
Those communities would be bacteria that derive their energy from inorganic compounds,including rocks.
The Perseverance rover does not have instruments to determine whether organisms exist today — just as previous Mars rovers and landers did not have the instruments needed to search for organics as well as the Perseverance rover can. But the rover clearly is giving scientists the ability to study the Martian surface as never possible before.