Powerful geysers erupt on Mars, sending jets of gas and dust hundreds of feet into the air, scientists have discovered. The dramatic event occurs every two years around the Red Planet’s frozen south pole as spring sunlight warms the ice.

Nasa experts say the powerful 100mph jets are caused by the release of carbon dioxide gas from beneath the martian icecap. There are thousands of the geysers every spring. Their existence solves the riddle of mysterious dark spots and spidery markings photographed by Nasa’s orbiting Mars Odyssey spaceprobe.

The dark features, between 50 and 150ft wide, appear for three or four months then vanish as winter forms a new layer of ice. US scientists examined images taken with a special thermal camera on Odyssey called Themis that reveals the temperature of Mars, the journal Nature reports.

Phil Christensen, of Arizona State University, described the dramatic scene on Mars for any astronaut visitor. He said: “All around you, roaring jets of CO2 gas are throwing sand and dust a couple hundred feet into the air. You’d also feel vibration through your spacesuit boots. The ice slab you’re standing on would be levitated above the ground by the pressure of gas at the base of the ice.”

He added: “Originally, scientists thought the spots were patches of warm, bare ground exposed as the ice disappeared. But observations made with Themis told us the spots were nearly as cold as the CO2 ice, which is at -198° Fahrenheit. A few places remained spot-free for more than 100 days. Then they developed a large number in a week.”

The scientists say the dark spots are the heavist debris that falls back from the eruptions. They also observed fan markings where lighter dust had spread in the wind. A further puzzle was the spider-shaped markings. These are explained as dust-filled grooves carved beneath the ice by the high-speed gas rushing towards the geyser vents.

(Image Credit: Arizona State University/Ron Miller)