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Hot Topic Solar System Mars Blown Away by Dry Mars?
Blown Away by Dry Mars?
based on ESA/Mars Express report
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Posted:   09/28/04

Summary: Where did all the martian water go? It is a basic question that has puzzled planetary scientists, even more now that evidence of past water becomes more comprehensive. One theory that the Mars Express orbiter is trying to test suggests that solar wind has scavenged volatile gases and liquids from the martian atmosphere.

Blown Away by Dry Mars?

Solis Planum
Perspective view. Solis Planum images were taken during orbit 431 in May 2004 with a ground resolution of approximately 48 meters per pixel. The displayed region is located south of Solis Planum at longitude 271° East and latitude of about 33° South.
Credit: ESA/Mars Express

Recent results from the ASPERA-3 instrument on board Mars Express confirm that a very efficient process is at work in the Martian atmosphere which could explain the loss of water.

Water is believed to have once been abundant on the Red Planet. Professor Rickard Lundin, leader of the ASPERA-3 team, describes these findings in a paper published in the latest issue of Science.

Mars is bombarded by a flood of charged particles from the Sun, commonly called the 'solar wind' and consisting of electrons and alpha particles. The solar wind erodes the atmosphere of Mars, and is believed to have stripped away a large amount of water that was present on the planet about 3800 million years ago.

Geological evidence, as recently confirmed by images from the High Resolution Stereo Camera (HRSC) onboard Mars Express, indicates that water flows and even an ocean in the northern hemisphere shaped the surface of Mars.

"I think it's increasingly evident that there is a large inventory of water on Mars." -Lisa Pratt, Indiana
Image Credit: NASA

Today, water still exists on the Red Planet, but less than in the past. Observations made earlier this year by the OMEGA instrument on Mars Express showed that Mars has vast fields of perennial water ice, stretching out from its south pole.

The ASPERA-3 instrument on board Mars Express aims to answer the question of whether the solar wind interaction with the upper atmosphere of Mars contributes to the depletion of water. It is measuring a process called 'solar wind scavenging', or the slow 'invisible' escape of volatile gases and liquid compounds which make up the atmosphere and hydrosphere of a planet.

Using plasma spectrometers and a special imager to detect energetic neutral atoms, ASPERA-3 is making global and simultaneous measurements of the solar wind, the inflow of energetic particles, and also the 'planetary wind', which is the outflow of particles from the Martian atmosphere and ionosphere.

Aspera 3 has established that the solar wind penetrates through the ionosphere and very deeply into the Martian atmosphere down to an altitude of 270 kilometers. This seems to be the reason for the acceleration processes that cause the loss of atmosphere on Mars.

From the start of January to the middle of February, Mars Express produced a total of 18 strips of pictures in 100 orbits of Mars. In general, one orbit produces an image with a length of over 250,000 lines, sometimes more, sometimes less.

Solis Planum
Perspective view. Solis Planum images were taken during orbit 431 in May 2004 with a ground resolution of approximately 48 meters per pixel. The displayed region is located south of Solis Planum at longitude 271° East and latitude of about 33° South.
Credit: ESA/Mars Express

From orbit, Mars Express is scanning the surface and atmosphere of the planet with seven instruments. In particular it will:

  • search for signs of water down to a few kilometres underground;
  • map the Martian surface more accurately than ever before (in colour and stereo);
  • determine the detailed composition of the surface;
  • determine the composition and circulation of the atmosphere;
  • study the interaction of the solar wind with the planet.

Mars Express is performing the most detailed and complete exploration of Mars ever done. When searching for water, for instance, Mars Express is conducting the most thorough search so far: from several kilometers below the ground, and up into the atmosphere. Before entering martian orbit, the cruise took just over six months. Mars Express travelled at an average speed of about 10 kilometers per second (around 2100 miles per hour) and covered a distance of about 400 million kilometers (240 million miles).

Mars Express's orbiter will operate for a whole Martian year (687 Earth days). It is expected that the mission will be extended by another Martian year. After the mission, the Mars Express orbiter will simply keep orbiting the planet for at least 50 years. Then it will probably burn up in Mars's atmosphere. This will also ensure that debris will not pollute the planet's surface. Many of Mars Express elements will be used for Venus Express, and probably other missions in the future.

A paper describing the results, by Professor Rickard Lundin and his collaborators was published in Science. Professor Rickard Lundin and Dr Stas Barabash from the Swedish Institute for Space Physics in Kiruna, Sweden, are the leading scientists responsible for the ASPERA-3 instrument, which results from collaboration with 15 other research groups in ten different countries.

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NASA Mars Exploration Program

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