Water on Mars?

[Brian G Turner]

Am I the only one cynical enough to question NASA's claim about massive amounts of water on Mars?

The announcements originally rode on the back of a claim that tons of hydrogen had been detectwed laying beneath the Martian crust - and NASA concluded that this was evidence of water, because the hydrogen must be in the form of water molecules. A reasoned assumption?

But it isn't - there are many forms that hydrogen atoms can exist in.

My own cynical suggestion would be that nothing more remarkable than huge salt basics have been located - salt basins comprised mostly of hydrous ferric salts.

When crystals form out of a water solution, water molecules are often trapped in large quantities within the crystal lattice. These compounds are referred to as existing in a hydrous state.

Hydrous Iron (II) Sulphate - FeSO4 [8 H2O] - for example, would be a particularly good candidate for any form of hydrogen present anywhere upon the Martian geosphere. As would Iron (III) and other metallic sulphates, nitrates, chlorides, etc.

Or does NASA know that already? After all, the water in hydrous salts is still water - it's just that you won't be able to scoop it up and drink it, as a NASA spokesman claimed in an earlier press release about the supposed discovery of water on Mars.

There's no great conspiracy theory here - the ISS (International Space Station) is clawing up almost all of NASA's funding. With water claimed present on Mars, NASA is now pushing for billions of dollars for a manned mission to the red planet.

Maybe I'm overcynical - maybe there really is pure water in various states on Mars. But if NASA really are over-exaggerating the entire issue to raise prospects for more funding, it won't just be our closest extra-terrestrial neighbour that begins to look red

 

[Survivor]

Well, you wouldn't be able to scoop it up and drink it in the literal sense anyway...Mars is still Mars and all.

As you say, water bound up in a hydrous ferric salt is still water, and can be liberated with the right equipment, most of which you would need if you were going to get to Mars in the first place.

The bottom line is that there is water in some form or other, and We want to send a guy up there to try and drink it

 

[nemesis]

If what you are saying is true then it is obviously proagandist. If NASA are staing that the water is liquid and fit to drink then they are being purposefully misleading. Anhydrolysing salts would not be easy on a large scale.

 

[Brian G Turner]

I actually think the whole issue of water on Mars is being highly exagerrated. I argued on another forum that I thought frozen carbon dioxide could be a potential contender for the formation of Martian "water channels". And now it was actually suggested in an article in this week's "New Scientist" - with the addendum of there still being lots of water. But once cynicism kicks into a topic, it's hard to take any part of it seriously. The idea of water on Mars is such a great propagandist march for an already financially embattled NASA that it's a shame both to criticise it and accept it.

 

[Brian G Turner]

Well, NASA overhyped the issue - but is their water on Mars, and if so, how much?

This interesting report from the BBC doesn't seem to have hit the science periodicals yet...

Water 'flows' on Mars

Dark streaks on crater and valley walls may indicate that brackish water currently flows across the surface of Mars.

New images and analysis suggest the slopes around the Red Planet's largest extinct volcano, Olympus Mons, contain dark stains caused by brine flowing down hill.

The discovery indicates that the substantial underground ice deposits on Mars can sometimes melt and flow across the surface.

It is bound to increase speculation that life may exist near to the surface of the planet.

The study has been done by Tahirih Motazedian, of the University of Oregon, US. It supports work done by others.

She told BBC News Online that she had examined images of Mars taken at different times and had seen new streaks form within time intervals of months.

She speculates that geothermal activity driven by volcanic heat may be causing the melting of subsurface ice.

The water dissolves surrounding minerals to form a super-saline brine which, because it contains salts, can remain liquid at lower temperatures and pressures than pure water can.

When the brine trickles on to the surface, it flows downhill staining the surface.

"The streaks originate from distinct geologic horizons below the Martian surface, where the water-ice table has been intersected by crater and valley walls," she said.

Significantly, the dark streaks are never overlain or cut by other features like craters or sand dunes, just as if they were made by water marking the surface.

"They passively overlay existing features except where they are forced to flow around obstacles," she said.

The dark streaks always begin upslope as a point and widen downslope, just like flowing water.

The streaks have the same dispersive patterns that liquid water has when it flows downhill, "highly indicative of dynamic fluid flow", says Tahirih Motazedian.

Images taken of the Mangala Valles region show that the dark streaks are being formed at the present time.

Two images taken a few months apart show new streaks have appeared.

"This demonstrates the existence of a currently active, short-term process of surface change on Mars," the researcher said.

 

[Survivor]

Of course they overhyped the issue. Well...technically I guess that you could "scoop it up and drink it"--assuming you had a straw or something to drink with through your suit--since this form is actually liquid on the surface. Wouldn't be a very good idea, and I don't see why we would want to send a guy to Mars to do something we already know would kill him in short order.

There is lots of water on Mars, it is driven out of the mantle and core by the same geological processes that gave Earth oceans in the first place. Much of it has evaporated into space, but the surface temperature over much of the planet is below freezing besides which there are chemically bound forms of water, as we have already discussed.

 

[Brian G Turner]

The particularly interesting point was that there was observation of a hydrological process in action.

As for the whole water issue - so long as NASA officials keep away from the "Enjoy Martian Ice Water" hype we can maybe see some interesting developments here soon - especially as we have the first European mission going out there very soon (not sure how the US mission plans are going after Columbia).

 

[Brian G Turner]

I've now split this topic to keep the Beagle 2 discussion separate.

Essentially, this thread was about the issue of water on Mars.

Now, here's a good BBC article on the matter:

Mars was a water world

Liquid water, not anything else, carved the canyons, valleys and outflow plains of Mars, according to the latest research.

A rival theory, that liquid carbon dioxide or rocks supported by CO2 gas could have made the surface features, does not work, according to Dr Neil Coleman, of the US Nuclear Regulatory Commission.

It could put an end to the "White Mars" hypothesis, which favoured CO2 and made the prospect for life on Mars more remote.

Vast lakes of water accumulating under sheets of ice until they overflowed crater and canyon walls is the way many Martian features formed, says Dr Coleman.

Neil Coleman has studied some of the most dramatic and significant scenery on Mars: the enormous outflow channels of Chryse Planitia.

Chryse Planitia may once have been an ocean. Today it is a huge plain where many of Mars' largest outflow channels converge. It was also Viking 1's landing site in 1976.

But what caused the outflow channels? Many scientists say obviously running water, but in recent years a few researchers have questioned this, arguing that liquid carbon dioxide might be responsible.

The White Mars hypothesis contends that gaseous or liquid carbon dioxide carried debris down Martian slopes and eroded the features some attribute to fluvial processes.

Advocates of the theory say it solves many problems with the water model, such as where the water came from and where it went.

Neill Coleman's work, published in the Journal of Geophysical Research, is, he believes, conclusive evidence that water, not carbon dioxide, is responsible for the features seen on the planet's surface.

Dr Coleman says his latest study shows that nowhere is the evidence for vast quantities of running water clearer than the outflow channels of Chryse Planitia.

Consider the associated Kasei Valles. He suggests it is a system of intertwined flood-carved channels more than 2,000 kilometres long that begins in near the equator in Echus Chasma and ends in Chryse Planitia.

He says the White Mars theory is "inconsistent with studies of terrestrial and Martian mass movements" because, "put simply, rocks can 'float' on air, but not for long".

This means that only water had the stamina to carve large-scale Martian features like Kasei Valles.

Advocate of the White Mars idea, Nick Hoffman of Australia's La Trobe University, says that Coleman's work is interesting but that he does not feel the White Mars idea is mortally wounded by it.

Another factor in favour of the water hypothesis is the discovery of reservoirs of water ice beneath the surface at Martian mid-latitudes and the fact that outflow channels on Mars are related to the planet's volcanic activity in the past.

This latest research indicates the outflow channels may have been carved by lakes of water trapped under ice that burst through crater walls and flowed downhill in torrents.
Only a liquid like water, says Dr Coleman, could have slowly accumulated under ice cover, and ultimately filled a basin until it overflowed.

Water-carved channels are good for the prospect for life on Mars hanging on at the present having been formed in the Martian oceans of three billion years ago.

Neil Coleman says: "In reviewing the White Mars hypothesis, we find even more evidence of water than expected, which bodes well for the search for life on Mars."

The special worth with that link is that it gives names to research. This is especially interesting because the notion of Mars being carved by CO2 processes actually exists under the umbrella of another theory: White Mars.

Here are some links:

Was Mars Always A Frozen Wasteland Devoid Of Life?

Most of the world’s recognized planetary scientists accept the model that Mars was once a warm and watery world.
Now a radical new Australian theory about the evolution of Mars suggests the planet may have always been a frozen wasteland devoid of life.

University of Melbourne geologist Dr. Nick Hoffman has evidence that is forcing these scientists to reassess their long-held beliefs about how Mars formed and whether there is, or ever has been, liquid water and life on the surface of Mars.

Dr. Hoffman has studied erosional features scarring the surface of Mars such as valleys, channels and gullies. He suggests that liquid and gaseous carbon dioxide (CO2) could be responsible for gouging out these features, not water, as believed by the majority of scientists.

NASA is looking for life on Mars based on the theory that liquid water once existed on the surface of Mars. If Dr. Hoffman’s theory proves correct, their search will be futile as they will have been searching in the wrong places and in the wrong way.

“We need to think more clearly about where life would be on Mars and how we could collect samples. If there is life on Mars it is likely to be many kilometers underground. By finding where water isn’t, you narrow down the sites worth looking for liquid water, and hence, life,” says Dr. Hoffman.

Dr. Hoffman and colleagues from the US Geological Survey (USGS) presented their most recent evidence in the latest Geophysical Research Letters.

Their research focused on gullies formed by areas of collapsed terrain along the rim of the 3.5 billion year old Hellas basin, an impact crater 2,000 kilometers wide and 9 kilometers deep.

Their data suggests that the gullies were scoured by debris helped along by flowing liquid and gaseous CO2 rather than hot springs or exploding groundwater as originally proposed.

Hoffman believes the Hellas Basin Gullies formed when volcanic magma mixed with trapped and compressed frozen carbon dioxide. This expanded violently, causing the ground to collapse and flow down the slope, gouging out a gully as it went. The now liquid and gaseous carbon dioxide acted as a lubricant for the debris to continue flowing.

Dr. Hoffman has also studied much younger gullies that may be still forming today or that formed within the last 10,000 years.

“Previous researchers have speculated that because of the frosty sub-zero temperatures around the location of the gullies, they must have been formed by hot groundwater or springs bursting through the surface. The presence of water would have also boosted their theory of the possibility of life on Mars,” says Dr. Hoffman.

“Data from my own observations of the gullies suggest that the flows, which occur each Mars Spring, occur by thawing of CO2 snow cover at a time when there was still solid CO2 (dry ice) on the surface and the ground temperature is around -130 degrees celcius,” he says.

“You cannot get anything water-based to flow at those temperatures. Even the most caustic cocktail we could make to lower the freezing point of water would fail to flow.

“But our modeling reveals it is possible to make a flow with the lubrication of gaseous CO2. As the carbon dioxide snow boils off, the gas would act like millions of tiny hovercraft transporting the rocky debris down the slope. Frozen carbon dioxide mixed with the debris could continue to boil off as the debris ploughed downwards, prolonging the flow.”

“Initially, planetary scientists deemed my theory impossible, but they appreciated the existence of an alternative view,” he says. “With this recent evidence, however, they now see the idea as possible and are starting to look at the data in detail.

“The ideas about liquid water on Mars arose nearly 30 years ago when the first Martian probes sent back images showing vast networks of channels, valleys and gullies.

“The space shuttle program then swallowed up any spare funding available for further research into the planets, so the theory of water on Mars just sat there.

“A whole new generation of scientists has grown up believing there is water on Mars because there was no other idea around. I have upset supporters of the water-based model by showing there is another idea that fits the data.

“In attempting to explain the flood channels as evidence of liquid water, planetary scientists have developed a host of concepts and models that are generally unworkable, often impossible, and collectively raise more problems than they solve."

Hoffman has consolidated his ideas into a model he calls "White Mars."

"‘White Mars’ brings together a broad range of observations and knowledge of flow processes to explain Mars in a single, simple, non-paradoxical model,” he says.

and the following link is to the site maintained by the geologist, Nick Hoffman, who appears to be the main opponent of the "wet Mars" theory: (note, it includes some interesting short illustrated articles)

White Mars

 

[nemesis]

There are theories but there is no reason to favour any until the data is in. Looking at fluid channels does not reveal the nature of that fluid. That is the issue here. Samples are required first.

 

[Brian G Turner]

Well, perhaps the MArs Express can answer some of the issues raised. Unfortunately, after much media fanfare yesterday, the launch never actually took place:

Nasa delays Mars mission

 

[Brian G Turner]

The plot thickens:

More evidence of water on Mars:

More evidence of water on Mars

A space craft has detected the best evidence yet of water on Mars.

Barely a year ago, Mars Odyssey found signs that the planet has reservoirs of underground ice near its south pole.

Scientists at the US space agency (Nasa) estimated there was enough ice to fill Lake Michigan twice.

They said it might be merely the tip of the iceberg and it seems they were right.

New observations by Mars Odyssey and Mars Global Surveyor (another Nasa probe that is mapping the Red Planet) suggest the north pole has about one third more underground ice than the south.

Beneath a shallow crust of dry soil, there appears to be a layer of permanently frozen ground that is up to 75% ice.

"If the conditions were warmer in the past, as they probably were, it may have led to the ice melting to form water which would be much more conducive to the presence of life," says William Boynton, one of a team of Russian and American astronomers behind the discovery.

The finding is exciting not just because it increases the possibility that microbial life could have evolved on a planet other than Earth.

It may also make human exploration of Mars more feasible because astronauts sent to the planet would need a source of water during their stay.

"From the point of view of human missions to Mars, it could be an outstanding discovery," says Bo Maxwell of the UK branch of the Mars Society.

"The big question is exactly how deep these deposits are and how pure they are."

There is now almost overwhelming evidence that Mars has reserves of frozen water hidden just below the surface.

The best evidence so far rests on the distinctive chemical signature of hydrogen in water, detected by an instrument on Mars Odyssey.

Landing a robotic space probe near one of the Martian poles to dig for ice could settle the argument, once and for all.

Ironically, Nasa's Mars Polar Lander, which was lost on descent in 1999, was equipped to do just that.

Scientists are now lobbying the agency to send an updated version of the craft back to Mars.

Unlike the ill-fated probe, it would carry biology experiments designed to search for microbial fossils.

"I think we need to revisit what Mars Polar Lander was going to do," says Boynton, of the Lunar and Planetary Laboratory, University of Arizona, Tucson. "To land on the ice and look for organic material that might be indicative of past life."

The latest research, reported in the journal Science, comes as Nasa prepares to launch the second of its Mars Exploration Rovers, named Opportunity.

The robotic explorer is following in the footsteps of its twin, Spirit, and Europe's Mars Express and Beagle 2 mission.

Spirit, Opportunity and Beagle will touch down on Mars after a six-month voyage. They are all heading for the mid-latitudes of Mars rather than the polar regions.

Nevertheless, the news is bound to be greeted with enthusiasm by the project teams, particularly Beagle, which carries experiments to search for life.

 

[Brian G Turner]

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."

 

[nemesis]

The most interesting point about the first article is that it is presented by the very same person behind the White Mars theory. Is it possible? Could be? But also could be a rare event.

 

[Brian G Turner]

This is very interesting - the article claims that there never was any extant ice on Mars - and it certainly contradicts some of the previous assertions against the White Mars theory:

http://news.bbc.co.uk/1/hi/sci/tech/3173167.stm

Mars 'not a watery world'

Hopes that Mars once had vast oceans of water and perhaps microbial life have suffered a setback.
A US space agency (Nasa) space craft has failed to find evidence that the Red Planet was once a warm, watery world like the Earth.

Scientists have been searching for decades for signs of water-related carbonate minerals on the Martian surface.

Mars Global Surveyor, which is orbiting the planet, has at last come up with the goods.

But it has found only traces of carbonates in dust, which probably came from the atmosphere rather than rocky outcrops deposited by oceans.

"What we don't see is massive regional concentrations of carbonates, like limestone," said Dr Joshua Bandfield, a planetary geologist at Arizona State University, Tempe. "We're not seeing the white cliffs of Dover or anything like that."

Some have argued that early in the 4.5 billion year history of Mars, its climate was much warmer and wetter.

If this was the case, oceans may have formed, producing extensive carbonate rock layers like those seen on Earth.

Mars Global Surveyor has been looking for signs of these rocks with its infrared spectrometer instrument.

The fact it has not found large quantities of carbonates suggests Mars is an icy wilderness that could never have supported life.

"This really points to a cold, frozen, icy Mars that has always been that way, as opposed to a warm, humid, ocean-bearing Mars sometime in the past," said co-researcher Dr Philip Christensen.

While the findings add weight to the view that Mars has always been a cold, inhospitable planet, they are unlikely to satisfy everyone.

Many scientists believe the argument will only be settled by landing robotic probes, and perhaps one day astronauts, on the Martian surface.

The European Space Agency's Mars Express space craft, carrying the Beagle 2 lander, is currently on the way to Mars.

Following close behind are two Nasa rovers that will search for geological evidence of water on Mars.

Beagle 2 and the Mars Exploration Rovers will land around Christmas, and more missions are planned for later in the decade.

Dr Jim Garvin, Nasa's lead scientist for Mars exploration, says the significance of the latest results may have to wait for the discoveries to be made by the Mars Exploration Rovers in 2004 and the Mars Reconnaissance Orbiter in 2006 and beyond.

"What's important is that we have found carbon-bearing minerals at Mars, which may be linked to the history of liquid water and hence to our quest to understand whether Mars has ever been an abode for life."

The research is published in the journal Science.

 

[Brian G Turner]

Seems like the water on Mars theory is going down the drain.

http://www.newscientist.com/news/news.jsp?id=ns99994120

Red planet's hue due to meteors, not water

Why is Mars red? The generally accepted explanation that liquid water rusted its rocks may be wrong. Lab experiments that mimic the environment on Mars suggest that the planet's reddish hue came from a dusting of tiny meteors falling on the surface. The result is fuelling the debate about whether Mars was ever hospitable to life.

The mineral that gives the planet its colour is a reddish iron oxide. Until now, astronomers thought that it probably formed in a chain of chemical reactions as iron in rocks dissolved into pools and rivers on the warm young planet. The iron oxidised, precipitated, and was then blown all over the planet.

But Albert Yen of NASA's Jet Propulsion Laboratory in Pasadena, California, began to doubt this after the Mars Pathfinder mission reached the Red Planet in 1997. The mission revealed that there is more iron and magnesium in Martian topsoil than within its rocks. This suggests the minerals actually came from the small, metal-rich meteors and dust particles that constantly fall onto Mars, says Yen. Calculations suggest they deposit five centimetres of surface layer every billion years.

If that is the case, Mars might not have been so wet after all. To test whether this topsoil would have needed water to oxidise and turn red, Yen exposed metallic iron to ultraviolet light, simulating sunlight, in a chamber containing gases similar to the Martian atmosphere at temperatures as low as -60 °C.

Red iron oxides started to form within a week. No water was necessary, Yen told this week's meeting of the American Astronomical Society's planetary science division in Monterey, California.

Giant pools

Yen does not claim water never flowed on Mars - the planet's networks of dry valleys and channels are good evidence that it did, he says. But flowing water seems to have played only a small role in weathering the surface.

"There is something of a paradox about Mars," agrees Joshua Bandfield of Arizona State University in Tempe. His team recently showed that the planet has no large deposits of carbonates, which should have formed if giant pools of water had persisted on the surface.

Bandfield suggests that liquid water must have occasionally burst out of the ground, carving channels and gullies, but that it quickly froze again in the frigid Martian climate.

Although the finding makes the evolution of life on Mars seem unlikely, Bandfield insists it cannot be ruled out: "There appears to be quite a bit more living going on in the Amazon rainforest than in the dry valleys of Antarctica. But if the question is whether or not life exists in either climate, the answer is yes to both."

Planetary scientists are hopeful that NASA's rovers will shed more light on Mars's history when they arrive at the planet in January 2004. Yen says they should resolve the question of whether there is enough meteor dust to explain Mars's colour.

"I'm sticking my neck out here and making a prediction - I believe that the Mars rovers will find nickel in the soil," he told New Scientist. Nickel is abundant in many meteors but rare in Martian rock.