Huge glaciers up to half a mile thick have been discovered close to the equator of Mars and are thought to be the remnants of an ice age on the planet.

The glaciers are thought to have been formed up to 100 million years ago and are the “most dramatic” evidence yet of climate change on Mars.

Hundreds of glaciers have been identified by researchers using ground-penetrating radar that allows them to see through a rocky layer of debris covering the ice.

The biggest of the glaciers are up to 13 miles long and more than 60 miles wide and represent a potential source of water for astronauts on missions to Mars. When they formed, the climate on Mars was much colder because the tilt of the axis on which the planet spins was much greater than it is now. This allowed ice sheets to extend far beyond the polar regions and towards, possibly even reaching, the Equator.

Dr James Head, of Brown University in the United States, said: “The tilt of Mars’s spin axis sometimes gets much greater than it is now, and climate modeling tells us that ice sheets could cover mid-latitude regions of Mars during those high-tilt periods.”

The glaciers were found between 60 and 30 degrees of latitude in the southern hemisphere and a similar band is thought to hold even greater quantities of ice in the northern hemisphere.

Dr Jack Holt, of the University of Texas at Austin, in the US, said: “It’s the most dramatic evidence for climate change on Mars. There’s been a fair amount in the past but this is by far the most dramatic.

He added: “If we can understand how climate works on Mars and how it changes, perhaps it can tell us a bit about Earth’s climate.

“There are many of these glaciers, hundreds of them scattered at these latitudes. It does add up to a lot of ice and increases the known water budget on Mars.

“These glaciers almost certainly represent the largest reservoir of water ice on Mars that’s not in the polar caps. In addition to their scientific value, they could be a source of water to support future exploration of Mars.”

The glaciers were identified in the Hellas Basin region using ground-penetrating radar equipment on the Mars Reconnaissance Orbiter spacecraft which was able to reveal what was beneath a layer of rocky debris estimated at 10 metres deep.

The blanket of rocks over the glaciers, one of which was calculated to be the size of Los Angeles, hid the ice from view but at the same time it protected it from vapourising.

Researchers involved in the study, published in the journal Science, believe the glaciers are likely to contain a frozen record of the Martian climate several million years ago.

“The ice should preserve some of the atmospheric chemistry in the planet’s past and provide us with a window on what the environment and climate was like,” said Dr Holt.

He thought it unlikely that there would be evidence of life on Mars preserved in the ice because it is thought that when the glaciers formed the surface of the planet were “not amenable” to life. Nevertheless, it was possible: “We really don’t know all the answers.”

In their report the research team concluded: “This ice survives from climatic conditions markedly different from today’s and is potentially accessible to future landed missions, not only for scientfic study but as a resource to support exploration.”

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