Searching for signs of ice on Mars is complex. To explore whether ice lurks beneath the surface of the Red Planet, ESA’s Mars Express uses its radar to probe the interior.
It sends low-frequency radio pulses at Mars and records how they are returned to the spacecraft. These pulses can penetrate some of the material comprising the planet’s crust, bouncing back to Mars Express when they reach a layer of a different density or composition. By analysing the time delays of these returned pulses, scientists can determine the properties of material lying beneath the surface.
This image shows radar echoes from Meridiani Planum, an area near Mars’ equator that is also being explored by NASA’s Opportunity rover.
In the image, reflected echoes from the surface and subsurface, separated in time delay, are plotted along the ground track of the spacecraft’s orbit. The bright white line crossing the frame marks the surface of Mars, while the faint, more diffuse line just below represents echoes from the base of a layer of buried material located far below the surface. [More at link]