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RE: Nakhlites

Opening the meteorite has produced some interesting results in identifying the presence of carbon in the middle of the specimen.” - Dr Caroline Smith, meteorite expert at the Natural History Museum.

Although life on Mars is one possibility the carbon may have be due to contamination while on Earth.

It is also possible the carbon could have formed on Mars through a non-biological process, such as during an impact event.“ - Dr Caroline Smith.

Source Natural History Museum in London.



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Martian meteorite

Scientists from NASA will present a paper in Houston that suggests a meteorite from Mars, found here on Earth, may contain evidence of life from the Red Planet.

The achondrite exploded over the Egyptian town of El-Nakhla, on June 28, 1911, breaking into about 40 fragments, one of which allegedly killed a dog. The Nakhla meteorite was later identified as belonging to an exclusive group of objects, known as SNC meteorites, a subgroup of which is the nakhlites, which are believed to have come from the surface of Mars.

Carbon-rich substance was found filling tiny cracks within the Martian meteorite.
The material resembles that found in fractures, or "veins", apparently etched by microbes in volcanic glass from the Earth's ocean floor.

"We don't exactly know what it means yet, but it's all over the thin sections of the Nakhla material" - Kathy Thomas-Keprta, Lockheed Martin.

The meteorite examined was held in London's Natural History Museum.
The Museum, which holds several intact chunks of the meteorite, agreed to break one open.
Proving carbon in Martian meteorites is indigenous - and not contamination from Earth - is crucial to the question of whether life once arose on the Red Planet.

Initial measurements support the idea that the "carbonaceous material" is not contamination.
Details will be presented at the Lunar and Planetary Science Conference in Houston, Texas, next month. The research team includes scientists who brought evidence for microbial life in another Martian meteorite, ALH84001, to the world's attention in 1998.

The Martian meteorites are an extremely rare class of rocks. They are all believed to have been blasted off the surface of the Red Planet by huge impacts; the material would have drifted through space for millions of years before falling to Earth.

"It gives people a degree of confidence this had never been exposed to the museum environment. I think it's too early to say how (the carbonaceous material) got there... the important thing is that people are always arguing with fallen meteorites that this is something that got in there after it fell to Earth. I think we can dismiss that. There's no way a solid piece of carbon got inside a meteorite" - co-author Colin Pillinger of the UK's Open University.

Analysis of the interior revealed channels and pores filled with a complex mixture of carbon compounds. Some of this forms a dark, branching - or dendritic - material when seen under the microscope.

"It's really interesting material. We don't exactly know what it means yet, but it's all over the thin sections of the Nakhla material" - co-author Kathie Thomas Keprta, of Lockheed Martin Corporation in Houston, Texas.

Previous studies of the forms - or isotopes - of carbon in the Nakhla meteorite found a component of which more than 75% is lacking any carbon-14.
Since all terrestrial life forms contain some carbon-14, this component was thought to be either indigenous carbon from Mars or ancient meteoritic carbon.
Professor Pillinger and colleagues are carrying out direct isotopic analysis of the carbonaceous material, but he admits terrestrial contamination is occurring when thin slices of the meteorite are made for analysis.
However, the ratio of carbon to nitrogen in the epoxy used to prepare the thin sections is very different from that of the carbonaceous material in the meteorite's veins.
If it is indigenous to Mars the "carbonaceous material" came either from another space rock that smashed into Mars hundreds of thousands of years ago, or a relic of microbial activity.
A resemblance between the material in the meteorite and features of microbial activity in volcanic glass from our planet's ocean floor further support the idea they are biological in origin.
If this were the case, the remains of these organisms and their slimy coatings might provide the carbon-rich material found in Nakhla.

Peter Buseck, regent's professor of geological sciences at Arizona State University says that he found no strong evidence of a biological origin for the carbon in the meteorite.
He added that it was difficult to determine the origin of carbon in rocks based on microscopy.

The 37th Lunar and Planetary Science Conference runs from 13-17 March in Houston, Texas, US.

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-- Edited by Blobrana at 18:40, 2006-02-08



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RE: Nakhlites

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The Allen Hills Martian meteorite, called ALH84001, comes from a crater is in the Eos Chasma, a branch of the enormous Valles Marineris canyon system on Mars.
The origin of the meteorite has been identified by the Mars Global Surveyor and Mars Odyssey spacecraft.
The rock, , has been the subject of intense study ever since 1996 when scientists from NASA's Johnson Space Centre reported that fossilised microbial life might be embedded inside it. The rock, which formed 4.5 billion years ago, was blasted from the surface of Mars around 17 million years ago by an impact and made its way to Earth, landing in Antarctica.

While the Johnson Space Centre claim remains highly controversial, the scientists say further study has bolstered the evidence for fossilised life in ALH84001. So the discovery of the rock's place of origin on Mars could make that spot a strong candidate for a future landing by robots or people searching for extraterrestrial life.
The analysis, based on the rock's mineral characteristics, was presented by Vicky Hamilton of the University of Hawaii at this week's meeting of the Meteoritical Society in Tennessee, US.
Hamilton looked for matches between the laboratory spectrum of the meteorite, a mix of orthopyroxene and basaltic minerals, and data from the Thermal Emission Spectrometer and other instruments on the orbiters.

"There was only this one place, in all the places we can look that aren't too dusty, that had a composition that was consistent with the ALH84001" - Vicky Hamilton.

Hamilton has further examined the data from the site using topographic and thermal data and high-resolution imagery.

"Putting this all together, it's all consistent with this being the source region".

The pinpointed area is a “lobate flow”, the kind that occurs when an impacting object strikes a fluid-rich soil, as is the case with many Martian craters. There is a crater about 20 kilometres in diameter there, which cratering studies have now shown indicates a large enough impact to eject the rock out of Mars' gravitational field.
There is no single "smoking gun" piece of evidence that proves this was the place the meteorite came from.

"There isn't any piece of information that makes this a unique interpretation, other than the fact that we haven't seen any other suitable places"

Everett Gibson, one of the Johnson Space Centre scientists behind the original findings of possible signs of life in ALH84001 says the picture put together by Hamilton is "fascinating”. And like his work, there was “no single line of evidence that says, ‘ah, this is it’".
The meteorite is believed to have first formed deep beneath the Martian surface, and was later transported to the shallow depth from which it was propelled into space.

The Eos Chasma location fits that. The 4-kilometre-high cliffs bordering the canyon have exposed rocks from various ages in the Martian past, and impacts or erosion could have brought the rock to the canyon floor - along with rocks from a major portion of Mars' history.
That makes it a prime site for a landing mission someday. It would be an opportunity to sample rocks from a wide variety of ages, all in one place. And, if it really is the launch pad from which ALH84001 began its interplanetary travel, it may also be the place where the mystery of whether the rock's unusual contents really are signs of ancient life is finally unravelled.

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A new chemical study of Martian meteorites implies that the planet has always been cold and was rarely above freezing.

The researchers have been able to determine the maximum temperature the rock experienced; and they find no evidence that it was ever warm. The meteorites are a record of surface conditions for four billion years.
They conclude that the water erosion features seen on Mars must have been made during very brief periods.

Although the current average temperature at the Martian equator is about minus 55 Celsius, many scientists believe that the Red Planet was once warm enough for water to have existed on its surface, and for long enough for life to possibly have evolved.
Deep canyons, dried up river beds and many examples of deposits left behind by running water are evidence that water has flowed on the surface.

But the recent analysis, by David Shuster of the California Institute of Technology and Benjamin Weiss of the Berkeley Geochronology Centre, of meteorites blasted from Mars seems to paint a different picture.

The new work involves two of the seven known "nakhlite" meteorites (named after El Nakhla, Egypt, where the first such meteorite was found), and the celebrated ALH84001 meteorite that some scientists believe shows evidence of past microbial activity on Mars.

The crystallization ages of nakhlites are 1.3-1.4 Ga, intermediate between those of the young shergottites and ancient ALH84001.
Using geochemical analysis techniques the researchers reconstructed a "thermal history" for each of the meteorites to estimate the maximum long-term average temperatures to which they were subjected.

"We looked at meteorites in two ways. First, we evaluated what the meteorites could have experienced during ejection from Mars, 11 to 15 million years ago" - Benjamin Weiss.

Their conclusions were that ALH84001 could never have been heated to a temperature higher than 350 Celsius for even a brief period of time during the last 15 million years.
The nakhlites, which also show very little evidence of shock-damage, were unlikely to have been above the boiling point of water during their ejection from Mars 11 million years ago.
Nakhlites probably formed as lava flows, and consist mainly of green augite crystals with some olivine in a very fine-grained blend of plagioclase, feldspar, pyroxenes, iron-titanium oxides, sulfides, and phosphates.
The other part of the research addressed the long-term thermal history of the rocks while they resided on Mars. The scientists did this by estimating the total amount of argon still remaining in the samples.
The gas argon is present in the meteorites as well as in many rocks on Earth as a consequence of the radioactive decay of potassium. A noble gas, argon is not very chemically reactive, and because the decay rate is precisely known it can be used to date rocks.
However, argon is also known to leak out of rocks at a temperature-dependent rate. The cooler the rock has been, the more argon will have been retained.
The researchers found that only a tiny fraction of the argon that was originally produced in the meteorite samples has been lost through the aeons suggesting that the Martian surface has been in deep-freeze for most of the last four billion years.

"The small amount of argon loss that has apparently taken place in these meteorites is remarkable. Any way we look at it, these rocks have been cold for a very long time.
The ALH84001 meteorite, in fact, couldn't have been above freezing for more than a million years during the last 3.5 billion years of history
" - David Shuster.

This new line of research is a puzzle given the contrary evidence of running water on Mars.

"Our research doesn't mean that there weren't pockets of isolated water in geothermal springs for long periods of time, but suggests instead that there haven't been large areas of free-standing water for four billion years. Our results seem to imply that surface features indicating the presence and flow of liquid water formed over relatively short time periods" - David Shuster.

In fact, the evidence shows that during the last four billion years, Mars has likely never been sufficiently warm for liquid water to have flowed on the surface for extended periods of time.
This implies that Mars has probably never had a hospitable environment for life to have evolved, unless biology got started during the first half-billion years of its existence, when the planet was probably warmer.
The study is bound to be controversial showing a disparity between those scientists who look at pictures of Mars to discern its history and those who study the only pieces of the planet we can examine in detail in the laboratory.


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