The search for life on Mars just got a lot more complicated.
While rovers like Curiosity and Persistence scour the surface in search of traces of ancient life, new evidence suggests that we may have to dig much deeper to find them. Any evidence of leftover amino acids from a time when Mars might have been habitable is likely buried at least 2 meters (6.6 ft) below ground.
This is because Mars, with its lack of magnetic field and weak atmosphere, is subject to a much greater amount of cosmic radiation on its surface than Earth. We know this, and we know that cosmic radiation destroys amino acids.
Now, thanks to experimental data, we also know that this process occurs on geologically very short time scales.
“Our results suggest that amino acids in Martian surface rocks and regoliths are destroyed by cosmic rays at much faster rates than previously thought,” says physicist Alexander Pavlov of NASA’s Goddard Space Flight Center.
“Current Mars rover missions drill down to about 2 inches (about 5 centimeters). At those depths, it would only take 20 million years to completely destroy amino acids. The rate of destruction of amino acids other than perchlorates and water is even higher. increases. “
Cosmic radiation is indeed a major concern for Mars exploration. An average human on Earth is exposed to about 0.33 millisieverts of cosmic radiation per year. On Mars, that annual exposure can exceed 250 millisieverts.
This high-energy radiation, streaming from energetic events such as solar flares and supernovae, can penetrate the rock, ionizing and destroying any organic molecules.
At one time, Mars is thought to have had a global magnetic field, and a much thicker atmosphere, much like Earth’s. There is also evidence – much of it – that liquid water once sat on the surface of Mars in the form of oceans, rivers and lakes.
This combination of features suggests that Mars may have been habitable (perhaps repeatedly) in its past.
One sign that may indicate the habitability of Mars is the presence of amino acids. These organic compounds are not biosignatures, but some of the most basic building blocks of life.
Amino acids combine to form proteins, and have been found in space rocks, such as the asteroid Ryugu, and the atmosphere of comet 67P. So they are not a sure sign of life, but finding them on Mars would be another clue pointing to the possible emergence of life at one point in time.
Pavlov and his team wanted to better understand the possibility of finding evidence of amino acids on the Martian surface, so they designed an experiment to test the hardness of these compounds.
They mixed amino acids with silica, hydrated silica, or mineral mixtures designed to simulate Martian soil consisting of silica and perchlorates (salts), and tested a Martian atmosphere mimicking the Martian atmosphere at different temperatures. Sealed them in tubes.
Then, the team irradiated the samples with ionizing gamma radiation, to mimic the dose of cosmic radiation expected on the surface of Mars over a period of about 80 million years. Previous experiments only depleted amino acids without soil simulators. This may have given an incorrect lifetime for the amino acid.
“Our work is the first comprehensive study where the destruction (radiolysis) of a wide range of amino acids under a variety of Mars-related factors (temperature, water content, perchlorate abundance) was studied and the rates of radiolysis were compared. was gone,” says Pavlov.
“It turns out that the addition of silicates, and especially silicates, with perchlorates significantly increases the destruction rate of amino acids.”
This means that any amino acid probably long-lived, some 100 million years ago on the surface of Mars, irradiated into nothing.
Given that the surface of Mars hasn’t been as hospitable to life as we’ve known it for much longer than we’ve known it—millions, instead of billions of years—the few centimeters that Curiosity and persistence can dig up amino acids is unlikely.
Both rovers have found organic material on Mars, but since the molecules could have been created by non-biological processes, they cannot be taken as evidence of life. Furthermore, the team’s research suggests that those molecules may have changed significantly since their formation by ionizing radiation.
There is other evidence to suggest that the research team may be on to something. Over and over again, material beneath the surface of Mars actually makes its way to Earth. Actually, amino acids have also been found in it.
“We have identified several straight-chain amino acids in the Antarctic Martian meteorite RBT 04262 in the Astrobiology Analytical Lab at Goddard that we believe originated on Mars (not contamination from terrestrial biology), although these amino acids in RBT 04262 The mechanism of its formation remains unclear,” says astronomer Danny Glavin of NASA Goddard.
“Since meteorites from Mars typically ejected from depths of at least 3.3 feet (1 m) or more, it is possible that the amino acids in RBT 04262 were protected from cosmic radiation.”
We may have to wait until we have more hardcore digging equipment on Mars to find out more.
research has been published in astronomy,