Turns out that the surface of Mars is stiffer and colder than previously thought.

New observations from NASA's Mars Reconnaissance Orbiter indicate that any liquid water that might exist below the planet's surface and any possible organisms living in that water would be located deeper than scientists had suspected.NASA made the discovery was using the Shallow Radar (SHARAD) instrument on the Orbiter, which revealed long, continuous layers stretching up to 600 miles or about one-fifth the length of the United States.

The radar pictures show a smooth, flat border between the ice cap and the rocky Martian crust, NASA said. On Earth, the weight of a similar stack of ice would cause the planet's surface to sag. The fact that the Martian surface is not bending means that its strong outer shell, or lithosphere, a combination of its crust and upper mantle, must be very thick and cold.

"The lithosphere of a planet is the rigid part. On Earth, the lithosphere is the part that breaks during an earthquake," said Suzanne Smrekar, deputy project scientist for Mars Reconnaissance Orbiter at JPL in a release.

Temperatures in the outer portion of a rocky planet like Mars increase with depth toward the interior. The thicker the lithosphere, the more gradually the temperatures increase. The discovery of a thicker Martian lithosphere therefore implies that any liquid water lurking in aquifers below the surface would have to be deeper than previously calculated, where temperatures are warmer. Scientists speculate that any life on Mars associated with deep aquifers also would have to be buried deeper in the interior.

The radar pictures also reveal four zones of finely spaced layers of ice and dust separated by thick layers of nearly pure ice. Scientists think this pattern of thick ice-free layers represents cycles of climate change on Mars on a time scale of roughly one million years, NASA said. The observations support the idea that the north polar ice cap is geologically active and relatively young, at about 4 million years.

More news from Mars is expected this month as NASA's Phoenix Mars Lander is scheduled to touch down on May 25 not far from the north polar ice cap. It will further investigate the history of water on Mars, and is expected to get the first up close look at ice on the Red Planet.

NASA said Phoenix will enter the top of the Martian atmosphere at almost 13,000 mph. In seven minutes, the spacecraft must complete a challenging sequence of events to slow to about 5 mph before its three legs reach the ground. Confirmation of the landing could come as early as 7:53 p.m. EDT.

"This is not a trip to grandma's house. Putting a spacecraft safely on Mars is hard and risky," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington. "Internationally, fewer than half the attempts have succeeded."