Although ice has always been known to exist on Mars, a better understanding of its depth and location could be vital to future human explorers, said the report in the United States journal Science. Most of this precious liquid escaped into space, but some of it stayed behind, transforming into ice and settling beneath the rocky surface.
Dundas's team first spotted some of the new ice deposits a few years ago in images from the Mars Reconnaissance Orbiter.
The cliffs are located in the northern and southern hemispheres of Mars, at a latitude of 55 to 58 degrees, which on Earth would be similar to Scotland or the tip of South America.
The underground ice has gradually been exposed by erosion, with researchers detecting it at depths ranging from two to more than 100 metres below the Martian surface. "What we've seen here are cross-sections through the ice that give us a 3-D view with more detail than ever before".
"This ice is a critical target for science and exploration: it affects modern geomorphology, is expected to preserve a record of climate history, influences the planet's habitability, and may be a potential resource for future exploration", the study says. "In the mid-latitudes, it's normally covered by a blanket of dust or regolith", loose bits of rock atop a layer of bedrock, said research geologist Colin Dundas of the US Geological Survey's Astrogeology Science Center in Flagstaff, Arizona, who led the study. Considering how dead and lifeless the surface of Mars has proven to be, it's nice to know that there are plenty of more interesting secrets waiting to be discovered just below ground. They could also make for accessible sites to extract water for human use, although that would obviously conflict with studying the ice's layers for clues to the past.
"Astronauts could essentially just go there with a bucket and a shovel and get all the water they need", said one of the report's authors, Shane Byrne of the Lunar and Planetary Laboratory at the University of Arizona. Not having readily accessible water on Mars would be a real headache, and something that could delay or slow down exploration and migration efforts, and possibly force astronauts to the poles, where ice is more readily available at the surface.
"If you had a mission at one of these sites, sampling the layers going down the scarp, you could get a detailed climate history of Mars", suggested MRO Deputy Project Scientist Leslie Tamppari of NASA's Jet Propulsion Laboratory, Pasadena, California. When does ice accumulate? Water ice can be used, of course, for life support as well as for making fuels for surface and space vehicles.
It has been known for some time that some locations on Mars have water ice just below the surface - but until now, there has been no accurate way to know just how much.
Thick deposits cover broad regions of the Martian mid-latitudes with a smooth mantle; erosion in these regions creates scarps that expose the internal structure of the mantle. The frozen water, now exposed to the elements, likely retreats a few millimetres each summer, but it doesn't completely disappear.
The ice probably started as snowfall that compacted into massive fractured layers.