MaRS (Mars Radio Science Experiment)will use the radio signals that convey data and instructions
between the spacecraft and Earth to probe the planet’s
ionosphere, atmosphere, surface and even interior.
Information on the interior will be gleaned from the planet’s
gravity field, which will be calculated from changes in the
velocity of the spacecraft relative to Earth. Surface
roughness will be deduced from the way in which the radio
waves are reflected from the martian surface. "Variations in
the gravitational field of Mars will cause slight changes in the
speed of the spacecraft relative to the ground station, which
can be measured with an accuracy of less than one tenth the
speed of a snail at full pace," says Martin Pätzold, MaRS PI
from Köln University, Germany.