Principal investigators of the spacecraft's six instruments, turned on since 5 January, presented their results at a press conference in Darmstadt, Germany on Friday.

The instrument that made the measurement, OMEGA, searches for the telltale signature of molecules such as water by studying the spectra of sunlight reflected from Mars.

Previous studies have only indirectly indicated the presence of water near the surface of Mars, including one in December 2001 that inferred water from hydrogen in the soil, said Jean-Pierre Bibring, principle investigator of OMEGA.

"I think you just saw a Eureka moment," added David Southwood, ESA's director of science, after Bibring presented a brightly colored image of the water ice.

Surprise result

It is summertime in the southern hemisphere of Mars, so finding water on the Sun-facing pole was unexpected, Southwood said, although swirls of carbon-dioxide ice cover the region. It's too early to tell whether the water ice means the south pole is simply colder than expected or whether there is more water than expected, he said.

Bibring said he and his team would release data on how much water they measured at a future date. Next week they will also look for water ice on the northern polar cap.

Other water-related results include a measurement of oxygen ions being blown off the planet's atmosphere by charged particles that make up the solar wind. The oxygen ions were most likely coming from atmospheric water vapor, which is known to exist in trace amounts, said Rickard Lundin, principal investigator of the ASPERA instrument that took the data.

Unlike Earth, Mars has no global magnetic field to fend off most of the solar wind. Researchers using ASPERA hope to find out if the solar wind is the main culprit responsible for the dearth of water on Mars today.

Also released today were spectacular images and videos made from the High Resolution Stereo Camera (HRSC), which has so far imaged 1.87 million square kilometers of the Red Planet.

Dustfall

Sinuous channels and pits similar to those eroded by water on Earth were imaged at a few meters' resolution, in full color, and in 3-D. "I think we can say, yes, there was water acting on the surface of Mars," said Gerhard Neukum, principal investigator of the HRSC.

The resolution makes it possible to see dust spilling over the lip of a caldera on the volcano Albor Tholus. "I call it a dustfall," said Neukum.

The data is flooding in too fast to make sense of some mysterious features, such as a dark splotch in Mars's grand canyon and along some valleys, he said. They may be sediments that OMEGA will be able to identify.

Testing and calibrating the spacecraft's six instruments will continue until 20 February, after which they will continue to take data. A radar probe that will study the top five kilometers of the planet's crust will also be deployed on 20 April.

Mars Express will continue to search for its missing lander, Beagle 2, by sight and telemetry, but Southwood said he was not optimistic about finding it. "It would have been the cherry on the cake, but the whole cake is there," he said, adding that the Mars Express mission's successes thus far should make every European proud.

(CRI January 24, 2004)