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5,000 orbits and counting

On December 25, 2003, Mars Express arrived at the Red Planet. Almost 4 years later, the orbiter has reached 5,000 orbits of Mars.
Provided by ESA, Noordwijk, Netherlands
Mars Express, imaged in an artist's impression above, left Earth on June 2, 2003 and reached Mars 6 months later.
ESA/D. Ducros
November 26, 2007
During its 5,000 orbits spent investigating Martian mysteries, Mars Express has revolutionized our knowledge of Mars. Some of the most visually astonishing results have been returned by the High-Resolution Stereo Camera (HRSC), which has produced breathtaking, 3-D color images of the diverse Martian surface.

One of the most surprising discoveries has been the youthful appearance of the country-sized volcanoes of the Tharsis ridge, suggesting they may have been active only a few million years ago. The images also show that glacial landforms are widespread over much of the planet, with glacial activity continuing in some areas until perhaps 20,000 to 30,000 years ago. Among the peculiar landforms imaged by HRSC is what appears to be a recently frozen body of water in Elysium, close to the equator.

While the camera has been imaging the surface in detail, other instruments have been examining different aspects of the planet's environment. One of the most significant results from the Visible and Infrared Mineralogical Mapping Spectrometer OMEGA has been the discovery of clays, hydrated minerals that formed early in the planet's history, when liquid water was fairly abundant. However, the presence of sulphates and iron oxides suggests that the planet subsequently became colder and drier, with only episodic eruptions of water onto the surface.

At the poles, OMEGA has measured the surface composition and produced maps of water ice and carbon dioxide ice. Further insights into the Martian poles have come from the Mars Advanced Radar for Subsurface and Ionospheric Sounding, MARSIS, which is revealing, for the first time, the secrets of the planet's subsurface.
This image of the Martian north polar ice cap shows layers of water ice and dust for the first time in perspective view. Here we see cliffs which are almost 2 kilometres high, and the dark material in the caldera-like structures and dune fields could be volcanic ash.
ESA/DLR/FU Berlin/G. Neukum
It has identified the presence of water ice deposits several kilometers underground and revealed fine, layered material near the poles. Similar soundings of the north polar cap have confirmed that it is dominated by water ice, with variable amounts of dust. The larger southern cap seems less dusty, but, with a maximum thickness of 3.7 km, it contains enough ice to produce a global ocean 11 meters deep.

The multi-frequency radar has also been probing the upper atmospheric layer (the ionosphere) and found that the distribution of charged particles is linked with patchy magnetic fields in the Martian crust.

Although Mars' atmosphere is very thin, it plays an important role in the planet's evolution. The Planetary Fourier Spectrometer (PFS) has made the most complete map to date of its chemical composition. Evidence for the presence of methane could indicate that volcanic activity, or even simple life forms may still be present today.
A partial view of the Martian south polar ice cap from an altitude of 269 kilometres light.
ESA/DLR/FU Berlin/G. Neukum
Meanwhile, the Ultraviolet and Infrared Atmospheric Spectrometer, SPICAM has provided the first complete vertical profile of the atmosphere's carbon dioxide density and temperature. It has revealed a nightglow and aurorae at mid-latitudes, produced the first ozone map and discovered the highest clouds ever observed on Mars.

The Energetic Atoms Analyser (ASPERA) has confirmed that the solar wind is slowly stripping atoms from the atmosphere down to an altitude of 270 km, although the rate of loss is surprisingly slow.

The MaRS radio science experiment has studied surface roughness by pointing the craft's high-gain antenna at the planet and recording the echoes. It has also been used to measure small changes in the spacecraft's orbit caused by gravity anomalies. Some of the most marked increases in surface gravity have been found over the volcanic Tharsis ridge, indicating a higher-than-average crustal density. Another discovery has been the existence of an ionospheric layer created by meteors burning up in the atmosphere.

With the mission already extended until at least 2009 and the possibility of further extensions into the next decade, ESA is keen to ensure that Mars Express will continue to provide the best possible scientific return.
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