Mars atmosphere was once rich with oxygen, say scientists. Where did it go?
Early Mars might have had both liquid water on its surface and oxygen in its atmosphere, according to a new study published in Geophysical Research Letters.
Findings by NASA鈥檚 Curiosity and Opportunity rovers reveal that, beneath the Red Planet鈥檚 dusty surface lurk , a compound likely created by a marriage of liquid water and atmospheric oxygen.
鈥淭his is a piece of the puzzle in our understanding of early Mars,鈥� study co-author Raymond Arvidson tells 海角大神 in a phone interview, 鈥渁nd the potential for habitation on a planet like Mars.鈥�
Manganese is very difficult to oxidize, according to the study鈥檚 lead author Nina Lanza, requiring large quantities of liquid water and a lot of oxygen.
Although other chemical reactions can oxidize manganese, Dr. Lanza tells the Monitor, oxygen is the most likely culprit.
When Curiosity found high concentrations of manganese oxide in a crater on Mars, Lanza says, scientists using the聽 (a rover tool that analyzes the chemistry rock and mineral samples) were surprised.
On Earth, manganese oxides are created by either the presence of oxygen, or tiny creatures called microbes. Researchers say that the former is far more likely on Mars than the latter.
Free oxygen on Earth was rare before life evolved and began the process of photosynthesis, explains Lanza, so oxygen can serve as a biosignature, or a sign that a planet has life.
But if Mars had enough oxygen to oxidize manganese, scientists may have to reevaluate the idea of oxygen as a biosignature, she says, as this provides evidence for a highly oxygen-rich atmosphere at one point in Mars鈥檚 history, but there is still no proof of life.
So where, then, did all of Mars鈥檚 oxygen go?
Into the rocks. 鈥淥xygen is very reactive,鈥� says Dr. Arvidson, 鈥渁nd unless you replenish it, it would be consumed very quickly.鈥�
As Mars鈥檚 liquid core cooled, probably about 4.2 billion years ago, its magnetic field grew weaker and weaker, leaving its atmosphere susceptible to solar winds.聽At that time, Mars likely had a lot more water than today. Without a magnetic field to protect it, radiation could have split water molecules into hydrogen and oxygen. Solar winds would have stripped away the lighter hydrogen atoms, leaving behind oxygen atoms to rust (oxidize) surface minerals and turn the planet red.
鈥淭his tells us that Mars has evolved very differently than we thought it did,鈥� Lanza told the Monitor. 鈥淲e need to start looking for different types of minerals and other evidence about Mars鈥檚 past.鈥� 聽
Researchers are quick to caution that the presence of a more oxygen-rich atmosphere does not mean that Mars ever played host to life, or that it was even truly Earth-like. But it is a clue.
鈥淚t is another piece of the puzzle,鈥� reiterates Arvidson.
鈥淭his is the first step towards understanding planets like Mars,鈥� says Lanza, 鈥渂ut it is not the last step.鈥�
