A study published last year in the journal Science suggested liquid water is present beneath the south polar ice cap of Mars. Now, a new study in the AGU journal Geophysical Research Letters argues there needs to be an underground source of heat for liquid water to exist underneath the polar ice cap.
The new research does not take sides as to whether the liquid water exists. Instead, the authors suggest recent magmatic activity – the formation of a magma chamber within the past few hundred thousand years – must have occurred underneath the surface of Mars for there to be enough heat to produce liquid water underneath the kilometer-and-a-half thick ice cap. On the flip side, the study’s authors argue that if there was no recent magmatic activity underneath the surface of Mars, then there is not likely liquid water underneath the ice cap.
“Different people may go different ways with this, and we’re really interested to see how the community reacts to it,” said Michael Sori, an associate staff scientist in the Lunar and Planetary Laboratory at the University of Arizona and a co-lead author of the new paper.
The potential presence of recent underground magmatic activity on Mars lends weight to the idea that Mars is an active planet, geologically speaking. That fact could give scientists a better understanding of how planets evolve over time.
The new study is intended to further the debate around the possibility of liquid water on Mars. The presence of liquid water on the Red Planet has implications for potentially finding life outside of Earth and could also serve as a resource for future human exploration of our neighboring planet.
“We think that if there is any life, it likely has to be protected in the subsurface from the radiation,” said Ali Bramson, a postdoctoral research associate at the Lunar and Planetary Laboratory at the University of Arizona and a co-lead author of the new paper. “If there are still magmatic processes active today, maybe they were more common in the recent past and could supply more widespread basal melting. This could provide a more favorable environment for liquid water and thus, perhaps, life.”
Examining the environment
Mars has two giant ice sheets at its poles, both a couple of kilometers thick. On Earth, it is common for liquid water to be present underneath thick ice sheets, with the planet’s heat causing the ice to melt where it meets the Earth’s crust.
In a paper published last year in Science, scientists said they detected a similar phenomenon on Mars. They claimed radar observations detected evidence of liquid water at the base of Mars’s south polar ice cap. However, the Science study did not address how the liquid water could have gotten there.
Mars is much cooler than Earth so it was unclear what type of environment would be needed to melt the ice at the base of the ice cap. Although previous research has examined if liquid water could exist at the base of Mars’s ice caps, no one had yet looked at the specific location where the Science study claimed to have detected water.
“We thought there was a lot of room to figure out if [the liquid water] is real, what sort of environment would you need to melt the ice in the first place, what sort of temperatures would you need, what sort of geological process would you need? Because under normal conditions, it should be too cold,” Sori said.
Looking for the heat
The new study’s authors first assumed the detection of liquid water underneath the ice cap was correct and then worked to figure out what parameters were needed for the water to exist. They performed physical modeling of Mars to understand how much heat is coming out of the interior of the planet and if there could be enough salt at the base of the ice cap to melt the ice. Salt lowers the melting point of ice significantly so it was thought that salt could have led to melting at the base of the ice cap.
The model showed salt alone would not raise the temperature high enough to melt the ice. Instead, the authors propose there needs to be additional heat coming from Mars’s interior.
Reference: “Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today” by Michael M. Sori and Ali M. Bramson, 12 February 2019, Geophysical Research Letters.