Life on Mars?
One thing that life on Earth requires liquid water, so conditions that enable the presence of liquid water is one of the key items on the planet habitability checklist. We know that Mars used to have surface water – we've seen evidence of it in Martian meteorites that have made their way from Earth, excavated from the red planet when the Solar System was still young. Today, however, Mars is dusty, dry and desolate, and any water on its surface is frozen.
The transition from a relatively wet planet to arid dustbowl is sometimes attributed to Mars's lost magnetic field. But it's possible that other factors play a role in the retention of volatiles, such as the surface gravity of a cosmic body; Earth's gravity, for reference, is 2.66 times that of Mars's. So Wang and his team set about investigating.
Specifically, they started looking at the abundances of the moderately volatile element potassium on various Solar System objects, using it as a tracer for other volatile elements and compounds.
That's because potassium isotope ratios are a strong proxy for volatile depletion in planetary interiors, because they are insensitive to igneous processes and impact-induced vaporization.
"Martian meteorites are the only samples available to us to study the chemical makeup of the bulk Mars," Wang says.
"Those Martian meteorites have ages varying from several hundred millions to 4 billion years and recorded Mars's volatile evolution history. Through measuring the isotopes of moderately volatile elements, such as potassium, we can infer the degree of volatile depletion of bulk planets and make comparisons between different Solar System bodies."
The team studied the isotope compositions of potassium in 20 Mars meteorites, chosen because they seem to be representative of Mars's bulk silicate composition. These compositions were then compared to the known bulk silicate compositions of three other inner Solar System objects of varying masses – Earth, the Moon, and the asteroid Vesta.
The results showed that Mars lost mor volatiles than Earth did during its formation, but retained more than the Moon and Vesta, both of which are significantly smaller and drier than Mars.
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