Today, ESA’s Mars Express orbiter flies almost directly over
the NASA Spirit rover at Gusev Crater at an altitude of about
300 kilometres. Mars Express uses four instruments to look
down, while Spirit looks up.

Mars Express will be looking down with its High Resolution
Stereo Camera and three spectrometers: OMEGA for
identifying minerals in infrared and visible wavelengths, and
the Planetary Fourier Spectrometer (PFS) and
SPICAM for studying atmospheric circulation and composition. Spirit
will be looking up with its panoramic camera and an infrared

Spirit’s science team will be able to take advantage of the
special possibilities presented by this pass of the European orbiter.
The aim is to get observations from above and below at the same time
to determine the dynamics of the atmosphere as accurately as possible.

The Mars Express observations are also expected to supplement earlier
information from two NASA Mars orbiters about the surface minerals and
geological features in Gusev Crater.

Dr Ray Arvidson, Deputy Principal Investigator for the
science instruments on the Spirit rover, said: "This is an
historic opportunity." Spirit’s infrared spectrometer, the
Miniature Thermal Emission Spectrometer (Mini-TES)
can be used to assess the temperatures in the Mars
atmosphere from the planet’s surface to a height of
several kilometres.

The Mars Express measurements are most sensitive for
the upper atmosphere, while Spirit’s measurements are
most sensitive for the lower portion of the atmosphere.

Agustin Chicarro, ESA’s Project Scientist for Mars
Express, said: "This is the first time that two space
agencies are co-operating on another planet with two
spacecraft. It is remarkable to know that one is in
orbit and one is on the surface, both taking
measurements to complement each other."