Mars was once a world with a huge ocean of liquid water, but that ocean is now trapped in space. According to new research, a wind of energetic particles and extreme ultraviolet light stripped away this water and its atmosphere around 3.7 billion years ago.
To understand how this happened, researchers measured the variability of 54Cr in meteorites ejected from Mars billions of years ago. They then estimated the impact rate and how much water these rocks delivered. They found that there would have been enough water to fill an ocean 300 meters deep (
Water Ice on the Surface
Mars has a thin atmosphere and the water ice on its surface evaporates quickly. This makes it an inhospitable place for microbial life to thrive, but it could be possible for water to survive on the planet temporarily, according to a study released last month.
In the mid-latitudes of Mars, water ice has been detected by NASA’s Phoenix lander and the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter (MRO). The icy material is thought to be the leftovers of dusty snowfall that fell on the Red Planet about a million years ago, and may still exist.
But until now, scientists haven’t known where the ice is located underneath the surface. That’s because it’s hard to get heat-sensitive instruments such as MRO’s Mars Climate Sounder and the Thermal Emission Imaging System on the Mars Odyssey spacecraft into very deep places on the planet.
Now, a team of researchers has discovered a region where water ice is hidden underground at the southern polar region. They used a new technique to analyze data from the Mars Global Surveyor spacecraft and found evidence of undulations in the ice cap’s surface that could be caused by liquid water beneath the ice.
Using computer model simulations of ice flow, the researchers found that undulations in the simulated ice cap’s surface were similar to those they saw on the real ice cap. They then inserted a patch of reduced bed friction in the simulated ice sheet bed where a body of liquid water, if present at the site, would allow the ice to slide and speed up.
The research, published in the journal Nature Astronomy, provides the first line of independent evidence that liquid water exists under Mars’ south polar ice cap. This is important because it means that the planet could still be geothermally active, allowing water to remain under the ice cap today.
The ice deposits are shallow and accessible with only minimal equipment, which is essential for future crewed exploration of the planet. This information is particularly useful because it will help mission planners find enticing landing sites for future spacecraft, which could bring humans to Mars in the future.
Liquid Water Under the Ice Cap
A body of liquid water under Mars’ ice cap would be a treasure trove for astronauts. It would be able to support life and provide essential nutrients, such as oxygen, rocket fuel, and drinking water.
Scientists have been speculating that there is a subglacial lake beneath the south polar ice cap on Mars for years. In 2018, an international team found evidence that it did exist, based on radar data from the European Space Agency’s Mars Express spacecraft.
The researchers used laser altimeters on the satellite to measure points on Mars’ surface and analyzed the data. It revealed a six to nine-mile-long surface undulation, comprised of a depression and a corresponding raised area. This was similar to the surface features observed over subglacial lakes on Earth.
Moreover, the researchers discovered similar patterns of surface movement in their simulations, which they believe suggest that the ice on the ground may be made up of liquid water. They ran computer model simulations of ice flow, adapted to Martian conditions, and then placed a patch of reduced bed friction in their simulated ice sheet, where liquid water, if present, would allow the ice to move.
They compared the results with observations of the radar reflectivity and found that they were consistent with an accumulation of liquid water on the Martian ice cap’s surface. This is a new way of thinking about the situation on Mars.
“Liquid water is something that we need to know about in order to be able to get a better idea of what could have happened in the past,” says Frances Butcher, a planetary scientist at the University of Sheffield and co-author on the study.
The researchers then analyzed the surface topography of the ice cap and found a large-scale undulation that consisted of a depression and a raised area. It deviated from the surrounding ice by several meters.
This is similar to the surface features seen over subglacial lakes on Earth, which are teeming with life and a source of vital nutrients for human civilizations. It suggests that there is a possibility for life to exist on Mars, but scientists will have to look further into it to determine whether or not it is possible.
Water Ice in the Soil
The Mars ice age is long gone, but some of the planet’s surface remains covered with a thin layer of ice. This ice has been detected on several areas of the planet, and some planetary scientists believe that it could have formed in Mars’ past.
The ice reaches to the surface at lower latitudes, but also extends into the soil. It’s known to occur in the Utopia Planitia region, an area wider than the state of New Mexico. The ice is thought to be a lake of water that may have existed on Mars at some point.
Scientists have long suspected that liquid water might exist under the ice cap, but they didn’t know how to tell if it was happening at a depth where the ice would be thick enough to be visible. In this study, a team of researchers used radar readings from NASA’s Mars Reconnaissance Orbiter to map water beneath the south polar ice cap.
They found evidence of a “raised bench” and a nearby “topographic depression”, 10-15 kilometre-long features that could have been created by liquid water. Using computer model simulations, the researchers then tested whether water could cause the undulations they observed on the ice cap’s surface.
If water were present, the ice would need to melt under the surface of the ground, and then the resulting liquid water would flow back down to the ice cap. This process is called deliquescence.
It could be a very useful mechanism to use to fuel up on the Red Planet, instead of having to ferry a lot of propellant from Earth. And, if it’s really true, then human missions to Mars could be more practical, because they won’t have to carry as much weight on their rockets.
The team’s findings, published in the journal Science, suggest that a subsurface layer of water ice might extend over as much as half the planet’s surface, from the poles to its mid-latitudes. It is the first time that scientists have identified such an area of subsurface ice, and it’s a huge step forward in Mars exploration.
It’s been a frenzied few years since scientists began to interpret small, bright radar reflections as spots of liquid water under the Martian ice cap. That idea was fueled by the observations of a probe called Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), which has been orbiting Mars since 2003 and is on a mission to investigate features below the surface of the planet.
The radar data appeared to show a 12-mile-wide (20-kilometer) patch of ice that is around a mile beneath the surface. It’s a hugely impressive find, given that the surface of the planet is essentially solid rock, not ice.
But this is not the first time that researchers have looked into the possible existence of subglacial lakes on Mars. In 2018, they found a 12-mile-wide region of possible ice beneath the south pole of the planet that they interpreted as a “lake” or “pond.”
That finding led to further analysis of the MARSIS radar signals, which pointed to a “blip” at the surface, about 12 miles wide, near the south pole. It resembled a “lake” that has been discovered under the Greenland and Antarctic ice sheets on Earth.
To test whether the blip was likely caused by liquid water at the base of the ice sheet, the team ran computer model simulations adapted to specific conditions on Mars. They added a patch of reduced bed friction and adjusted the amount of geothermal heat in the simulated ice flow to generate undulations that matched the ones they saw on the surface of the ice cap.
These patterns of ice flow are similar to those that appear over subglacial lakes on Earth, where the water lowers the friction between the ice and its bed, allowing the ice to slide and speed up. The resulting surface undulations are about six to nine miles (10-15 km) long and consist of a depression and a raised area, both of which deviate from the surrounding ice by several meters.
While this evidence gives the best indication yet that there is liquid water on the surface of the planet, the scientists warn that it does not mean that life is present. It would be extremely difficult for life to survive in such extreme conditions, and it is also likely that the water would be very salty, making it even harder for microbial life to thrive.