Mars Express: Polar Water-Ice Imaged

One of the main targets of the Mars Express mission is to discover the presence of water in one of its chemical states. Through the initial mapping of the South polar cap on 18 January, OMEGA, the combined camera and infrared spectrometer, has already revealed the presence of water ice and carbon dioxide ice.

OMEGA observed the southern polar cap of Mars on 18 January 2004, as seen on all three bands. The right one represents the visible image, the middle one the CO2 (carbon dioxide) ice and the left one the H2O (water) ice. Banner image shows the high resolution stereo camera and its reconstructed deep view. The location is east of the Hellas basin at 41° South and 101° East. The area is 100 km across, with a resolution of 12 m per pixel, and shows a channel (Reull Vallis) once formed by flowing water. The landscape is seen in a vertical view, North is at the top. Credit: ESA/DLR

Such infrared imagery will show aqueous minerals well in infrared wavelengths (0.35-0.5 microns) and is diagnostic for water bound in rocks, or aqueous minerals like clays, hydrated carbonates, sulfates, iron oxides as water-bearing, even nitrates.

"I did not expect to be able to gather together – just one month after the Mars Orbit Insertion of 25 December – so many happy scientists eager to present their first results", said Professor David Southwood, ESA Director of Science. Mars Express, ESA’s first mission to Mars, will reach its final orbit on 28 January. T o set the spacecraft into its final operational orbit, its path follows a highly elliptical polar orbit, taking Mars Express as close as 260 kilometers from the Martian surface, and out to more than 11, 000 kilometers away at its furthest from the planet.

The spacecraft has already been producing results since its first instrument was switched on, on 5 January. The significance of the first data was emphasized by the scientists at a European press conference Friday at ESA’s Space Operations Centre, Darmstadt, Germany

This presence of both water-ice and frozen carbon dioxide was confirmed by the PFS, a new high-resolution spectrometer of unprecedented accuracy. The first PFS data also show that the carbon oxide distribution is different in the northern and southern hemispheres of Mars.

Mars Clouds
Seasonality over Martian sols

The Mars Radio Science Experiment, or MaRS instrument, is a sophisticated radio transmitter and receiver that also emitted a first signal successfully on 21 January that was received on Earth through a 70-meter antenna in Australia after it was reflected and scattered from the surface of Mars. This new measurement technique allows the detection of the chemical composition of the Mars atmosphere, ionosphere and surface. "We aim to run the experiment for the next four years, providing a better understanding than ever before of the daily and seasonal variations that occur in the Martian atmosphere," says the MaRS Principal Investigator Martin Pätzold, of Universität Koln.

To gain this information, scientists on Earth must transmit a precise signal to Mars Express, which then sends it back, unchanged, once Mars Express has moved close to the limb of Mars. Here the radio signal has to pass through the thin atmosphere of Mars.

The temperature, density and pressure of the atmosphere cause subtle changes in the signal that are detected on Earth and which, when analysed, allow the scientists to see what the atmospheric conditions are on Mars.

Equally astonishing is that MaRS can detect minuscule variations in the movement of Mars Express. Mars Express needs only to vary its expected motion by just half the speed of a garden snail and this too will be detected by the MaRS analysis software.

These movements are caused by the spacecraft passing over Martian features such as mountains or the polar caps, whose masses cause tiny variations in the gravitational pull on Mars Express compared to when the spacecraft is flying over a flat plain or basin.

The data will be invaluable in determining the thickness of the planetary crust and charting the seasonal variation in the carbon dioxide ice sheets that make up the Martian polar caps.

ASPERA, a plasma and energetic neutral atoms analyser, is aiming to answer the fundamental question of whether the solar wind erosion led to the present lack of water on Mars. The preliminary results show a difference in the characteristics between the impact of the solar wind area and the measurement made in the tail of Mars. Another exciting experiment was run by the SPICAM instrument (an ultraviolet and infrared spectrometer) during the first star occultation ever made at Mars. It has simultaneously measured the distribution of the ozone and water vapour, which has never been done before, revealing that there is more water vapour where there is less ozone.

ESA also presented pictures produced with the High Resolution Stereo Camera (HRSC). They represent the outcome of 1.87 million km2 of Martian surface coverage, and about 100 gigabytes of processed data. This camera was also able to make the longest swath (up to 4000 km) and largest area in combination with high resolution ever taken in the exploration of the Solar System. This made it possible to create an impressive picture 24 meters long by 1.3 meters high.

Such data will allow planetary scientists on Earth to construct more accurate computer programs to simulate or ‘model’ the behaviour of the Martian atmospheric circulation. This ability could prove invaluable to future mission planners, especially for those scientists contemplating landing sensitive equipment, or even manned missions on the surface of Mars, perhaps as part of ESA’s proposed Aurora programme.

Planet at a Glance


  • One of five planets known to ancients;
  • Mars was Roman god of war, agriculture and the state
  • Yellowish brown to reddish color;
  • occasionally the third brightest object in the night sky after the Moon and Venus

Physical Characteristics

  • Average diameter 6,780 kilometers (4,212 miles);
  • about half the size of Earth, but twice the size of Earth’s Moon
  • Same land area as Earth, reminiscent of a rocky desert
  • Mass 1/10th of Earth’s;
  • gravity only 38 percent as strong as Earth’s
  • Density 3.9 times greater than water (compared to Earth’s 5.5 times greater than water)
  • No planet-wide magnetic field detected; only localized ancient remnant fields in various regions


  • Fourth planet from the Sun, the next beyond Earth
  • About 1.5 times farther from the Sun than Earth is
  • Orbit elliptical;
  • distance from Sun varies from a minimum of 206.7 million kilometers (128.4 millions miles) to a maximum of 249.2 million kilometers (154.8 million miles);
  • average distance from the Sun 227.7 million kilometers (141.5 million miles)
  • Revolves around Sun once every 687 Earth days
  • Rotation period (length of day) 24 hours, 39 min, 35 sec (1.027 Earth days)
  • Poles tilted 25 degrees, creating seasons similar to Earth’s Environment

Atmosphere composed chiefly of

Extreme Explorers' Hall of Fame
The wide angle view of the martian north polar cap was acquired on March 13, 1999, during early northern summer. The light-toned surfaces are residual water ice that remains through the summer season. The nearly circular band of dark material surrounding the cap consists mainly of sand dunes formed and shaped by wind. The north polar cap is roughly 1100 kilometers (680 miles) across.Credit: NASA/JPL/Malin Space Science Systems


  • carbon dioxide (95.3%),
  • nitrogen (2.7%) and
  • argon (1.6%)
  • Surface atmospheric pressure less than 1/100th that of Earth’s average
  • Surface winds up to 80 miles per hour (40 meters per second)
  • Local, regional and global dust storms; also whirlwinds called dust devils

Surface temperature

  • averages -53 C (-64 F);
  • varies from -128 C (-199 F) during polar night to 27 C (80 F) at equator during midday at closest point in orbit to Sun


  • Highest point is Olympus Mons, a huge shield volcano about 26 kilometers (16 miles) high and 600 kilometers (370 miles) across; has about the same area as Arizona
  • Canyon system of Valles Marineris is largest and deepest known in solar system; extends more than 4,000 kilometers (2,500 miles) and has 5 to 10 kilometers (3 to 6 miles) relief from floors to tops of surrounding plateaus
  • "Canals" observed by Giovanni Schiaparelli and Percival Lowell about 100 years ago were a visual illusion in which dark areas appeared connected by lines.
  • The Mariner 9 and Viking missions of the 1970s, however, established that Mars has channels possibly cut by ancient rivers Moons
  • Two irregularly shaped moons, each only a few kilometers wide
  • Larger moon named Phobos ("fear"); smaller is Deimos ("terror"), named for attributes personified in Greek mythology as sons of the god of war

Related Web Pages

European Space Agency
Exiting the Martian Ice Age?
Jet Propulsion Laboratory
Malin Space Systems
Mars Global Surveyor
Arizona State THEMIS
Mars 2001 Odyssey