Ancient Mars was even more Earth-like than scientists thought, new research suggests. The Curiosity rover has discovered high concentrations of manganese oxide minerals in the rocks of the Red Planet, suggesting that the Martian atmosphere contained more oxygen billions of years ago than it does today.
“The only option on Earth that we know to make these manganese materials involves atmospheric oxygen or microbes. Now we have found manganese oxides on Mars, and we are surprised how they could have formed,”said lead author Nina Lanza, a planetary scientist at Los Alamos National Laboratory in New Mexico.
Since there is no evidence that life ever existed on Mars, Lanza and her colleagues are leaning toward an explanation with atmospheric oxygen. Martian manganese oxides may have formed when rock interacted with liquid water under oxidizing conditions, Lanza says. Observations by Curiosity and other spacecraft have shown that liquid water was abundant on Mars, at least in some places, billions of years ago.
Lanza and her colleagues believe the gas began to form shortly after Mars's magnetic field closed about 4.2 billion years ago. The loss of the magnetic field caused the solar wind to sweep away the atmosphere of Mars (which was once dense enough). Moreover, without this magnetic field, high-energy ionizing radiation could reach the Martian surface, the researchers say.
This radiation then splits many of the water molecules into their constituent hydrogen and oxygen atoms. Extremely light hydrogen jetted into space, but Mars's gravity trapped the heavier oxygen that had accumulated. Then, over the past several billion years, oxygen levels have dropped significantly. In particular, the idea suggests that atmospheric oxygen is not an indicator of life, since high concentrations of matter can accumulate, apparently through abiotic processes.
Burmas Roman