Red Planet holds surprises
2005-09-08 07:43
Cambridge - Just half a lifetime ago, Mars was seen as Earth's sister, a future home-from-home, possibly also a rival - the Red Planet, where loathsome aliens plotted invasions of our home.
Then, in the 1960s, came the hammer blow.
Blurry pictures sent back by early space probes depicted Mars as a terrifying orange desert, parched and dusty, clearly incapable of nurturing any life. The fourth rock from the Sun suddenly seemed to be just that: a rock.
Today, thanks to a flotilla of US and European space missions, yet another picture is emerging.
No one should be tempted to revive any of the verdant fantasies of sci-fi, for no sign has emerged yet of life on Mars, past or present.
But the evidence now firmly states this: Mars is not dead, for it has plentiful reserves of water and maybe lingering sources of heat, too.
"It is partly a museum planet because of things that happened long ago, but it's also still an active planet," European Space Agency (ESA) scientist Gerhard Neukum said at a major conference on the Solar System.
"There's still water coming out in some places from aquifers underground... we see fog in low-lying areas in the morning and we see evidence of drainage when we go back to areas and look at them again and again."
Neukum this week presented the latest images sent back by Europe's Mars Express spacecraft, which he says suggest that the Red Planet has reserves of underground ice which have been melted by local hot sources and driven to the surface.
Occasionally active volcanoes?
"Fan-shaped" deposits, characteristic of recent water flows, lie at the edge of Olympus Mons, the highest mountain on the planet.
Ice also encrusts the mountain's western scarp, on ridges between six and ten kilometres high, as well as polar regions, he said.
Most of Mars' volcanic activity petered out around 1.5 billion years ago, but carried on in some areas until as recently as two million years ago, Neukum said.
But the latest Mars Express images also show a million-square-kilometre flank of the Martian north pole that appears to be studded with up to 100 non-active volcanoes.
They do not appear to have signs of cratering or wind erosion that typically suggest ancient volcanoes.
In other words, said Neukum, they are very recent - and, he speculates, some may even now be occasionally active.
A new Nasa study says that gullies around 500 metres long are formed in some Martian locations when water pops up to the surface.
Our closest neighbour
Finding water would be a godsend to any future manned mission to Mars, providing astronauts with fuel, through hydrogen, as well as the means to grow food and survive.
"The gullies may be of prime importance for human exploration," said Jennifer Heldmann of Nasa Ames Research Centre in California.
"They may represent locations of relatively new surface liquid water, which can be accessed by crews drilling on the Red Planet."
Mars clearly has a catastrophic history.
One theory is that around 3.5 billion years ago, the planet somehow lost its core-driven magnetic field, a shield that protected it against the fierce buffeting of particles from the Sun.
Without this, the planet's thick carbon dioxide atmosphere was progressively shredded by the solar wind and its precious oceans slowly evaporated.
Experts at the conference said they were beguiled by readings of relatively high levels of methane in what remains of Mars's atmosphere.
On Earth that would be explicable either by reaction between basalt rocks and water, or by biology: methane-emitting bugs that inhabit swamps, for instance.
If this latter theory is ever confirmed, it would prove that life does exist outside of Earth - and that our closest neighbour is a microbe.