MARS: Once a Water Planet?

BBC Science -- A huge, frozen sea lies just below the surface of Mars, a team of European scientists has announced. Their assessment is based on pictures of the planet's near-equatorial Elysium region that show plated and rutted features across an area 800 by 900km. The team think a catastrophic event flooded the landscape five million years ago and then froze out. They tell a forthcoming edition of Nature magazine that sediments covered the ice, locking it in place. Large reserves of water-ice are known to be held at the poles on Mars but if this discovery is confirmed by follow-up observations, it would be a first for a region at such a low latitude. "It's been predicted for a long time that you should find water close to the surface of Mars near the equator," Jan-Peter Muller, from University College London, UK, said.   "This is an area where there are a lot of river features but no-one has ever seen a sea before, and certainly no-one has ever seen pack ice before," he told the BBC News website. The interpretation is based on images taken by the High Resolution Stereo Camera on Europe's Mars Express spacecraft. These show extensive fields of large, platy features - reminiscent of the fractured ice floes found in polar regions on Earth. Finding exposed ice at the equator would be unlikely. Very low pressures on the planet would lead to sublimation - the ice would erode over time straight to water vapour. But the research group, led by John Murray, from the Open University, UK, tells Nature that a crust of dust and volcanic ash, perhaps just a few centimetres thick, has prevented this happening. "The story runs that water flowed in some kind of massive catastrophic event; pack ice formed on top of that water and broke up, and then the whole thing froze rigid," explains Professor Muller.  (02/23/05)

Don't be Afraid of the Dark

BBC Science -- Astronomers say they have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter. The team, led by Cardiff University, claimed it is the first to be detected. A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars. It was found 50 million light years away using radio telescopes in Cheshire and Puerto Rico. The unknown material that is thought to hold these dark galaxies together is known as 'dark matter', but scientists still know very little about what that is. The five-year research has involved studying the distribution of hydrogen atoms throughout the Universe, estimated by looking at the rotation of galaxies and the speed at which their components moved. Hydrogen gas releases radiation that can be detected at radio wavelengths. In the Virgo cluster of galaxies, they found a mass of hydrogen atoms a hundred million times the mass of the Sun. The mysterious galaxy has been called VIRGOHI21. Similar objects that have previously been discovered have since turned out to contain stars or be remnants of two galaxies colliding. However, the scientists from the UK, France, Italy and Australia found no visible trace of any stars, and no galaxies nearby that would suggest a collision. Dr Robert Minchin, of Cardiff University, said: "From its speed, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone. If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope." (02/23/05)