The Martian equator is surprisingly bereft of ice. Researchers used data from NASA’s Mars InSight lander to search for underground ice and natural mineral cements that form when water seeps underground, and they found very little evidence for either – which might make hunting for signs of past life on Mars even tougher.
InSight’s main scientific instrument is its seismometer, which measures seismic waves rattling through the ground. These waves move at different speeds depending on the material they are propagating through – the denser the material, the faster the waves – allowing researchers to deduce the structure of the rocks.
at the University of California, San Diego, and his colleagues used seismic data from InSight to examine the top 300 metres of the ground beneath the lander, near the equator of Mars. They ran a set of 200,000 computer simulations comparing the seismic waves to models of possible compositions for the area under the lander.
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The researchers found layers of sand and layers of rock, but neither had much ice – there was barely any in the sand, and only enough to fill up to 20 per cent of the pores in the rock. It also didn’t seem to have much natural cement, which tends to form as water sinks into the ground and creates clay-like substances that bind grains of sand together.
That’s surprising, because Mars was once home to rivers and seas of liquid water on its surface, and researchers thought that some of that water may have been absorbed into the ground. At least near the equator, though, that doesn’t seem to have happened.
“What we’re seeing here is that relatively little of the water got incorporated in cements in this area,” says Wright. “So we have to find a different place where that water went.” Some of it is stored in ice near the planet’s poles and some was most likely lost to space, but that’s not enough to account for the amount of water it appears that Mars once had.
This may also make it harder to find signs of past life on Mars. “Ice and other types of mineral cements could preserve a record of what was in the pores and fractures of rocks,” says Wright. “If there was ever life, the cements are one way that you could preserve the record of it, and here we’re saying you have minimal amounts of cements.”
Geophysical Research Letters
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