The Ice Sheet on Mars is Even Thicker Than Previously Believed

Maybe Mars isn’t as dry as we thought. ESA’s Mars Express has revealed new details about a region near Mars’ equator that could contain a massive deposit of water ice several kilometers deep. If it is indeed ice, there is enough of it in this one deposit that if melted, water would cover the entire planet up to 2.7 meters (almost 9 feet) deep.

But ice is just one explanation for the unusual features detected by the orbital spacecraft. Another is that this is a giant pile of dust several kilometers deep — although the dust would still need to have some ice mixed in.

Mars Express has been orbiting Mars since December of 2003 and back in 2007, the spacecraft studied the Medusae Fossae Formation (MFF), a large geological formation that includes wind-sculpted ridges and grooves, abrupt mesas, interspersed with smooth and gently undulating areas. The region extends intermittently for more than 5,000 km (3,100 miles) along the equator of Mars, extending from just south of Olympus Mons to Apollinaris Patera, with a smaller additional region closer to Gale Crater, where the Curiosity rover is exploring.

Various spacecraft in addition to Mars Express, such as NASA’s Mars Global Surveyor and Mars Odyssey, have also detected subsurface ice, as much as 2.5 km (1.5 miles) deep.

Now, new data from Mars Express suggest layers of water ice stretching even further underground – the most water ever found in this part of the planet.

“We’ve explored the MFF again using newer data from Mars Express’s MARSIS radar, and found the deposits to be even thicker than we thought: up to 3.7 km (2.3 miles) thick,” said Thomas Watters of the Smithsonian Institution, USA, lead author of both the new research and the initial 2007 study, in an ESA press release. “Excitingly, the radar signals match what we’d expect to see from layered ice, and are similar to the signals we see from Mars’s polar caps, which we know to be very ice rich.”

Watters and his team say that if melted, the ice contained within the MFF would cover the entire planet in a layer of water 1.5 to 2.7 m deep, enough to fill Earth’s Red Sea.

But MFF’s windswept landscapes contains one of the most extensive deposits of dust on Mars, which is possibly the biggest single source of dust on Mars. Some studies determined the strange features in this landscape could have been formed by explosive volcanoes.

In the 2007 observations with Mars Express, the radar data showed the MFF to be relatively transparent to radar and low in density – two characteristics which would reveal icy deposits. However, scientists couldn’t rule out a drier possibility: that the features are actually giant accumulations of windblown dust, volcanic ash or sediment.

But the beauty of long-lasting spacecraft is that it provides the opportunity for multiple observations of a single region on Mars over many years, providing additional follow-up data for study.   

“Here’s where the new radar data comes in! Given how deep it is, if the MFF was simply a giant pile of dust, we’d expect it to become compacted under its own weight,” said co-author Andrea Cicchetti of the National Institute for Astrophysics, Italy. “This would create something far denser than what we actually see with MARSIS. And when we modelled how different ice-free materials would behave, nothing reproduced the properties of the MFF – we need ice.”

The new results instead suggest layers of dust and ice, all topped by a protective layer of dry dust or ash several hundred meters thick.

We do know that massive stores of ice near the equator could not have formed in the planet’s present climate.

“This latest analysis challenges our understanding of the Medusae Fossae Formation, and raises as many questions as answers,” says Colin Wilson, ESA project scientist for Mars Express and the ESA ExoMars Trace Gas Orbiter (TGO). “How long ago did these ice deposits form, and what was Mars like at that time? If confirmed to be water ice, these massive deposits would change our understanding of Mars climate history. Any reservoir of ancient water would be a fascinating target for human or robotic exploration.”

If this does turn out to be large stores of water ice, the MFF deposits would be an incredibly valuable resource for any future human exploration of Mars. These types of missions would need to land near the planet’s equator, due to landing constraints, and resources like abundant solar power, and more moderate temperatures. The presence of equatorial water ice could provide a steady supply of water for a future base on Mars.

Further reading: ESA