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 Tuesday, 28 January, 2003, 14:22 GMT
Mars 'needs age revision'
Mars, Nasa
Surface age is worked out by counting craters

The way scientists have worked out the geologic age of the surfaces on Mars could be seriously in error, a new study suggests.

The findings are important because they challenge thinking which also influences theories about whether or not the Red Planet once sustained life.

"This has the potential to change everything we thought we knew about the age of different surfaces on Mars," Dr Tracy Gregg, assistant professor of geology at the University of Buffalo, US, said of her work.

The study could also cause researchers to reconsider the use of a critical tool employed by geologists to estimate the age of all planetary surfaces - that of counting the craters left by space impacts.

'Basic time marker'

The new view of Mars' history is possible because of research on an area called Hesperia Planum, which has been used since the 1980s to define the Hesperian epoch, the second of the planet's three geologic time periods.

"For almost 20 years, Hesperia Planum has served as the basic time-marker on Mars," said Dr Gregg.

In recent years, analyses of images obtained by the Mars Global Surveyor spacecraft have provided new estimates for the duration of the Hesperian epoch, ranging from just 300,000 years to 1-2 billion years, according to Dr Gregg.

The difference is a puzzle for planetary geologists. For her part, Dr Gregg has tried to figure out which surfaces on Mars originated in the Hesperian epoch, and then looked at them to define the duration of the Hesperian epoch.

"When we want to identify how old rocks are without the benefit of samples, we count impact craters, the big holes in planetary surfaces that are made by meteorites that crash into them," said Dr Gregg.

"The more impact craters there are on a surface, the older it is."

Life chances

Crucially, during the course of Dr Gregg's research reviewing images of Tyrrhena Patera, a volcano located in the middle of Hesperia Planum, she began finding deposits from more than one Martian geologic epoch.

According to Dr Gregg, this means that "Hesperia Planum is not one age. Its surface actually is a combination of materials that are very old, materials that are very young and some that are in between - and the volcanoes there are the reason why".

Dr Gregg has shown that two volcanoes in western Hesperia Planum were active for a much longer period than previously thought and that the dust and ash from them travelled much further than was realised.

She said the new observations about the great distances travelled by deposits of Martian volcanoes and their influence on the age of surfaces might lead to a reconsideration of the understanding of the history of Mars.

"I think that we are about to discover that Hesperia Planum, this surface that has acted as a basic time-marker for Mars, has a very different age than we thought," she said.

"If it turns out it's much older than we thought, then it means that the global geologic system shut down a lot earlier and the chances of finding active living organisms on Mars are much slimmer.

"If, on the other hand, it turns out to be much younger, then it means Mars still may be volcanologically active, and if it is, that increases the possibility of extant life on Mars."

See also:

07 Jan 03 | Science/Nature
28 May 02 | Science/Nature
23 Jun 00 | Science/Nature
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