Mars may not be as dead as we think. Scientists have discovered substantial deposits of icy water buried in shallow soil near the equator of Mars. The find could rekindle hopes of finding life on Mars, or that future human settlers can find a water supply. However, it also poses a mystery to climate scientists.
The results come from a reanalysis of data from NASA’s Odyssey spacecraft, which began orbiting Mars in 2001. This is the oldest working mission ever launched from our planet.
One of Odyssey’s instruments is dedicated to measuring the neutrons launched from the Martian surface by cosmic rays striking the planet. From this neutron count, scientists can find the amount of hydrogen and therefore calculate the amount of water present in the highest meter of the ground.
In small amounts, water can take many forms, be it hydrated minerals or small ice particles stuck between sand particles. But when the amount of water rises above 26% , as is the case in some regions, scientists are fairly certain that the ice is just below the surface. It’s a statement by Jack Wilson, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
Several regions of Mars are potentially rich in water (dark blue), including large areas near the equator. / JT Wilson et al., Icarus (2017).
That Mars has ice is not news. At the poles, there are permanent masses made up of frozen water and carbon dioxide. As early as 2002, researchers using Odyssey’s neutron instrument reported evidence of subsurface water at high latitudes. The evidence was strong enough that NASA sent the Phoenix Lander robot to explore these regions. And sure enough, when the robot’s arm scratched the ground in 2008, it found ice just below it.
Now, Wilson and his colleagues have found a way to map previously obtained Odyssey data at a 290-kilometer resolution , nearly double that of previous maps. They looked for smaller and more concentrated patches of ice water than previous analyzes might have shown. Thus, they found many of these bodies of icy water at much lower latitudes than expected , the researchers report.
“When we finally send people to Mars, we want to go where there is water,” says Jim Head, a planetary geologist at Brown University.
The mystery of the climate of Mars
But the ice patches also pose a challenge to climate scientists. According to current models of the climate of Mars, equatorial ice cannot persist for more than 125,000 years. That’s because the ice gradually sublimates into the atmosphere, even if it’s buried under a shallow layer of insulating soil. But, if the ice does exist there, it could be evidence of a change in the axis of rotation of Mars within this time frame, Wilson explains. This would mean that the planet is not dead at all.
Unlike Earth, Mars does not have a large moon to help balance the wobble of its orbital axis. And if the planet’s axis were tilted more than 25 degrees, some polar caps would have sublimated and they would have moved to lower latitudes. However, Wilson acknowledges that the explanation is unlikely, given that the axis of rotation of Mars should not oscillate on such fast timescales. Another possibility, he says, is that the soil also provides a vapor barrier to prevent sublimation.
Regardless of how equatorial ice got there, if it finds its way to the surface and melts, it could provide a welcoming habitat for microbes. That’s why scientists on Mars are so excited about so-called recurring slope lines , the dark streaks on steep slopes that are believed to be possible water seepage, either from melting ice or from underground aquifers.
Despite new evidence, NASA still believes that the current climate on Mars is not hospitable to organisms on Earth. Still, a human team could provide a stationary heat source that, in the long term, could melt underground ice and create a “hot pool” capable of supporting life.
References:
Water ice found near Mars’s equator could entice colonists and life-seekers. (2017). Science. doi: 10.1126 / science.aao6995
Image: NASA / JPL-Caltech / ASU
