More on the issue of the existence of water on Mars, with claims of ice stacks being present, not to mention the postulated use of radon detection as being used as an indicator for locating water more specifically on Mars.
Martian warm spots could be towers of ice: Martian warm spots could be towers of ice
Unusual warm spots on Mars might represent "ice towers" similar to those seen in Antarctica, say researchers. They could even harbour life, Nick Hoffman of Melbourne University told a conference on Thursday.
Hoffman detected warm spots in the Hellas Basin after scrutinising infrared images taken with THEMIS, the heat-sensing camera on the Mars Odyssey orbiter. The spots are about 10 degrees warmer than their surroundings both night and day, and irrespective of whether they are being hit by sunlight.
The simplest explanation, claims Hoffman, is that the warm spots are caused by some kind of geothermal activity causing the release of water vapour. If so, they could resemble the ice towers found on Mount Erebus, an active volcano on Ross Island in Antarctica, where the conditions are almost as cold and dry as on Mars.
The Mount Erebus towers are 10-metre tall chimneys of ice and are found nowhere else on Earth. They are created when the steam from volcanic vents hits the intense cold of the Antarctic air and condenses directly into ice, says Hoffman's colleague Phil Kyle of New Mexico Tech in Socorro.
"It's really fascinating," says Malcolm Walter, director of the Australian Centre for Astrobiology at Macquarie University in Sydney. "Anything about Mars is going to be speculative, but this is a really good working hypothesis for the [future] exploration of Mars."
No one has investigated whether the Mount Erebus towers harbour microbial life, although microbes are known to thrive in far harsher conditions in Antarctica. On Mars, such icy towers would be doubly good for life because not only would they be relatively warm, but the ice would filter out some of the dangerous ultra-violet radiation.
Furthermore, the Hellas Basin is at low altitude, and therefore has relatively high atmospheric pressure. This means there is a chance that the ice might melt to provide liquid water as it sometimes does in the Mount Erebus towers, says Hoffman.
The warm spots could be investigated visually as early as 2004, when the clouds are expected to clear over the Hellas Basin, a giant impact crater in the planet's southern hemisphere. That would provide the opportunity for the Mars Global Surveyor to capture high-resolution photos of the area, suggests Hoffman. The ice towers could grow as high as 30 m in the lower Martian gravity, and would stand out against the darker soil.
Hoffman is best known for his theory that liquid water and life probably do not exist on Mars, arguing that carbon dioxide snow, rather than liquid water, etched out the gullies seen.
But Hoffman does not think his new idea is contradictory. Instead, he says that to settle the debate, the next generation of exploration needs to look in the places most likely to harbour liquid water, such as the warm spots in the Hellas Basin.
"These are the locations on Mars where you are mostly likely to find liquid water, and they would be very easy to find because they will have these ice towers like signposts," he says.
Hoffman presented the new work at the 6th International Conference on Mars in Pasadena, California.
ALSO! Radon leaks could reveal water on Mars:
Sniffing for puffs of radioactive radon gas could be the easiest way to find water lurking metres beneath the Martian soil.
We already know there should be plenty of water on Mars. Probes have found water vapour in the Martian atmosphere and ice on the surface at the poles. And NASA's Mars Odyssey spacecraft recently detected traces of hydrogen, almost certainly bound up in ice near the surface.
But Mars Odyssey's sensors could only peek into the top metre of soil, and although the European Space Agency's Mars Express - due to reach the planet in December - has surface-penetrating radar that can spot water, it can only probe to between 100 metres and 5 kilometres underground.
That leaves a gap between 1 and 100 metres. NASA plans to send another craft to probe this depth with radar in 2005. But while radar is great at finding liquid water, it has a hard time distinguishing between ice and solid rock.
Now Jean-Christophe Sabroux from the Institute for Radiological Protection and Nuclear Safety in Saclay, France, says radon is the answer. Radon is produced by the radioactive decay of uranium, which is common in rocks on Earth and Mars.
The reaction kicks out radon at high speed, so the gas often embeds itself in a nearby mineral grain. But if there is water or ice in the way, the radon slows as it passes through. Without enough energy to dig itself in, the radon gas diffuses upwards and emerges at the surface (see graphic).
Radon has a short half-life, and on Earth it diffuses only a few metres through the ground before decaying. On Mars, however, where atmospheric pressure is low, the radon should be able to travel up to 20 metres.
That means a standard alpha-particle detector - which weighs just a few tens of grams, has no moving parts and consumes only a fraction of a watt - could be used to detect surface emissions from underground ice reserves.
Even if radon does show up, it will still be tricky to work out how much ice there is or where exactly it lies. And it is possible that background radiation from cosmic rays could drown out the signal. But if no radon is detected, it will mean the soil is definitely dry. "It's so straightforward," says Sabroux.
And since determining the presence of ice and water on Mars is vital to the search for life, he notes, it is best to have as much data from as many different methods as possible.
The idea for a radon sensor has now been added to a French proposal for a NASA mission in 2009. "One can expect a great scientific outcome for a minute outlay, so why not?" says Sabroux.
Daryl Dixon, a radon expert from the UK's National Radiological Protection Board in Chilton, Oxfordshire, thinks Sabroux could be onto something. "In principle the theory is sound. But it's hard to know how it would pan out on another planet," he says. "It's worth a shot, certainly."