In orbit

Kasei Vallis. Copyright ESA/DLR/FU Berlin (G. Neukum) Mars Express continues to capture spectacular images of the Martian surface, including this one of Kasei Vallis, one of the largest outflow channels on the planet. It was captured using the probe's High Resolution Stereo Camera (HRSC) from an altitude of 272 km above the planet's surface.

The great detail of the image reveals the history of erosion of the area. The light streaks show the result of wind forces on the planet and it is believed that part of the outflow was shaped by glaciers or water from lakes below the glaciers.

The image mimics the appearance the features would have to the human eye. In practice atmospheric dust and haze make this difficult to achieve.

Earlier, the HRSC imaged the crater at the summit of Olympus Mons, the highest volcano in the solar system. This is the first high-resolution colour image of the entire crater.

The crater, known as a caldera, is approximately 3 km deep and sits on top of the volcano which has an average elevation of 22km. A perspective view of part of the caldera has been produced using data from the HRSC.

European Space Agency (ESA) scientists have confirmed the presence of water ice beneath the surface on the south polar cap. OMEGA, the combined camera and infrared spectrometer on-board Mars Express made the initial discovery on 18 January 2004. It was later confirmed by a new high-resolution spectrometer (PFS) which is capable of unprecedented accuracy.

Scientists have also revealed many images showing channels on the surface that were probably created by flowing water. The image of the Reull Vallis was taken by the HRSC shows what appears to be sediment left in the bottom of river-shaped valleys.

Approaching Mars

Detail of the complex caldera of Olympus Mons. Copyright: ESA/DLR/FU Berlin (G. Neukum) As Mars Express approached the red planet, the HRSC took this image of Mars on 1 December 2003 from a distance of about 5.5 million km.

This is a very unusual view of Mars because the planet is illuminated in a way never seen from Earth. The Sun shines on part of the western hemisphere, but more than a third of the Martian disc lies in the dark.

The dark features at the top are part of the northern lowlands of Mars, where oceans may have existed billions of years ago.

Europe heads to Mars

On the evening of 2 June 2003 the European-built probe Mars Express launched from Baikonur spaceport in Kazakhstan. It was carried aloft on a Russian Soyuz/Fregat launcher and after an hour and 32 minutes was placed on a trajectory that would send it all the way to Mars. With Mars Express being the first ESA probe to go to Mars, the trouble-free launch was a relief to the project team.

At the time, Earth and Mars were unusually close meaning the spacecraft had to travel a relatively short distance. ESA took advantage of this to save fuel and reduce costs – an important part of the project's original conception.

Southern part of the Olympus Mons caldera – perspective view. Copyright: ESA/DLR/FU Berlin (G. Neukum) Travelling through interplanetary space at a speed of over 3 km per second or 108,000 km/h, the probe took just over six months to reach its destination. In order to conserve power, most of the probe's systems were deactivated during the journey, only coming online to contact Earth once every day.

Conception

The idea for Mars Express originated following the failed Russian Mars 1996 probe which was to deliver an orbiter and two landers to the planet.

In the aftermath of this set back and the costly loss of NASA's Mars Observer, many of the world's major space agencies decided that the one-off, costly missions pursued in the past presented too great a gamble.

In the future exploration programmes would run at reduced costs, strive for greater efficiency and be developed over shorter timescales.

Mars Express is the first European example of such a mission with a total budget of only 150 million Euros – half that of previous missions to Mars.

Why Mars?

Reull Vallis: HRSC image 15 January 2004. Copyright: ESA/DLR/FU Berlin (G. Neukum) For much of the last century, Mars has been the subject of both scientific and popular curiosity. Recent interest has been greater than ever following finding evidence of ancient water features on the surface and the discovery of possible microbial life forms in the Martian meteorite ALH 84001. The planet remains one of the solar system's few contenders for supporting life, past or present and is also the prime candidate for manned missions beyond the Earth-Moon system.

Mission objectives

The main objective of the mission is to search for evidence of sub-surface liquid water. Its presence would indicate whether Martian life is or was a possibility. Water ice did exist at the Martian poles and more recent space missions have discovered traces of water vapour in the thin atmosphere.

Evidence that water also existed in liquid form comes from images of structures on the planet's surface. Geological features have been interpreted as valleys and ancient river beds caused by flowing water and massive formations thought to result from catastrophic flooding. It has been suggested that the planet was relatively warm and wet until around 1.3 billion years ago, and possibly as little as 600,000 years ago when the climate changed suddenly. The planet's atmospheric pressure and temperature decreased rapidly causing Mars to become the cold, dry world it is today.

Mars as seen from Mars Express about 5.5 million km away. Copyright: ESA Water may still be present beneath the surface in the form of underground rivers, pools, aquifers or permafrost. Mars Express will conduct a global search for such reserves, using the orbiter's Sub-surface Sounding Radar in conjunction with Beagle 2 on the surface.

Additional goals

Mars Express will carry eight instruments, including Beagle 2 and perform many of the experiments originally carried on Mars 96. Following the release of the Lander and the attainment of a stable orbit, the remaining seven remote observation instruments carried by the orbiter will be used to accomplish a number of scientific goals. These include producing three-dimensional images of the surface using a stereoscopic camera, and using a radar instrument to penetrate the surface, allowing different materials and structures to be detected through their differing echoes and completing an accurate mineralogical survey.

Data will be obtained on the composition and evolution of the Martian atmosphere. Spectrometers will be used to produce high-resolution maps of atmospheric composition and global atmospheric circulation, and to investigate the interaction between the Martian atmosphere and the interplanetary medium. These data may also explain the particularly high oxidising capacity of the atmosphere, a phenomenon which causes iron atoms in the ground soil to be stripped of electrons and become rusty and gives the planet's surface its characteristic reddish hue.

Extended mission

Mars Express. Copyright: ESA-D DUCROS Following the completion of its primary mission objectives, Mars Express will continue to function for at least another Martian year (687 Earth days). The orbiter carries a communications package designed to relay data back to Earth from international Mars lander missions between 2003–07.

If successful Mars Express will increase our understanding of the planet, hopefully proving the existence or absence of liquid water and possibly microbial life forms. It will be the precursor to many space missions operating under the Mars Express philosophy of lower costs, greater efficiency and faster development times. The mission may also improve our knowledge of the history of Mars and as a result provide insights into the future atmospheric and geological evolution of our own planet.