Search for ice on Mars

Source: Agencies  |   2008-6-18  |     NEWSPAPER EDITION

IS the white stuff discovered in Martian soil ice or salt?

That's the question bugging scientists in the three weeks since the Phoenix lander began digging into Mars' north pole region to study if the arctic could be habitable.

Shallow trenches excavated by the lander's robotic arm have turned up specks and even stripes of mysterious white material mixed in with the clumpy, reddish dirt.

Phoenix merged two previously dug trenches over the weekend into a single pit measuring a little over 30 centimeters long and 7.5 centimeters deep. The new trench was dug at the edge of a polygon-shaped pattern in the ground that may have been formed by the seasonal melting of underground ice.

New photos showed the exposed bright substance present only in the top part of the trench, suggesting it's not uniform throughout the excavation site.

Phoenix will take images of the trench over the next few days to record any changes. If it's ice, scientists expect it to sublimate - or go from solid to gas, bypassing the liquid stage - when exposed to the sun because of the planet's frigid temperatures and low atmospheric pressure.

"We think it's ice. But again, until we can see it disappear ... we're not guaranteed yet," said mission scientist Ray Arvidson of Washington University in St Louis.

Even if it's not ice, the discovery of salt would also be significant because it's normally formed when water evaporates in the soil.

Preliminary results from a bake-and-sniff experiment at low temperatures failed to turn up any trace of water or ice in the scoopful of soil that was delivered to the lander's test oven last week.

Scientists planned to heat the soil again this week to up to 982.22 degrees Celsius.