Mars’ north pole is layered, scientists say

Mars’ north pole, like a French parfait, comes in layers.

Scientists analyzing radar images from NASA’s Mars Reconnaissance Orbiter spacecraft have found up to seven distinct layers of ice and dust beneath the north pole.

Roger J. Phillips, a scientist with the Southwest Research Institute in Boulder, Colo., said the layering was probably caused by changes in the planet’s orbit over the last 4 million years.

When the planet tilts strongly on its axis, the surface ice withers and is covered by a layer of dust mixed with ice, Phillips said. Then, “every million years or so,” he said, the planet tilts less, meaning less sunlight falls directly on the pole. At that point, a layer of clean ice is laid down.

The discovery, published today in the journal Science, comes as NASA’s Phoenix spacecraft closes in for a May 25 landing at the north pole. Phoenix carries a drill to dig into the surface ice.

The radar aboard the Mars Reconnaissance Orbiter also shows the weight of the ice cap has not deformed the underlying Martian crust, Phillips said. For this to be true, the hard crust layer must be more than 200 miles thick.

“This means the inside of Mars is colder than we thought it was,” Phillips said.

That has implications for any rudimentary forms of life that might exist on Mars. Despite the planet’s hostile surface, some scientists have speculated that bacteria or some other primitive life forms might be able to survive underground, where heat from the planet’s core could produce layers of liquid water.

Based on this new research, any such life forms must be deep underground, close to the core.

“Wherever they are, they are deeper than we thought,” Phillips said.

The Mars Reconnaissance Orbiter, built by Lockheed Martin Corp. in Denver, was launched in 2005 from Cape Canaveral in Florida. It has been orbiting Mars since 2006.

The mission is managed by the Jet Propulsion Laboratory in La Canada Flintridge.

 john.johnson@latimes.com