segunda-feira, 30 de julho de 2012

Tissint meteorite helps build Museum Martian library

 Museum scientist Natasha Stephen gets ready to analyse a tiny sample of the Tissint Martian meteorite. © Diamond Light Source

It may sound like a place where Martians sit and read books, but the Natural History Museum's Martian library is in fact a database of Martian meteorites, which has had a huge boost with the arrival of the Tissint meteorite.

Rare meteorites

Meteorites from Mars are incredibly rare - there are only 65 known in the world. The Tissint Martian meteorite fell to Earth in Morocco last July.

Crucially, it landed in the dry conditions of a desert and was picked up soon afterwards, so scientists think its contamination levels are likely to be much lower than other meteorites, making it even more valuable than others.

Terrestrial rocks
Up until now, most Martian research has been done by studying non-Martian meteorites and rocks from Earth (terrestrial rocks).

The planet Mars. It's our closest neighbour and many of its rocks are similar to Earth's.
This is because no samples have been collected directly from Mars - it would be too expensive and Mars is too far away. Only electronic data is sent back.

Although they are non-Martian, terrestrial rocks are still very useful because Mars has canyons and once had active volcanoes, meaning many of its rocks are similar to Earth's.

And now Museum scientist Natasha Stephen and colleagues can add data from the important Tissint specimen to the Museum's Martian meteorite library.

Natasha says, 'Tissint provides us with a rare and exciting opportunity to study a potentially very fresh piece of the Martian surface, something that is invaluable to planetary scientists until we have an actual sample collected from Mars'.

Meteorite composition 

3D map of Infra Red data from the Tissint Martian meteorite, taken at Diamond Light Source.
Natasha is investigating the mineral and geochemical composition of Martian meteorites. As part of this, she is collecting Fourier Transform Infra Red (FTIR) spectral measurements, using state-of-the art analytical facilities at the Museum and at the Diamond Light Source in Oxfordshire, UK.

The FTIR readings give unique 'signatures' for each of the minerals in the rocks. These can identify what type of rock it is, and suggest where on Mars it may be from. This will be the first ever Martian-specific mineral database of IR data.

'Adding data from Tissint to our library gives a more complete view of the composition of these rocks and how weathering and alteration can affect them.

'Using "fresh" data alongside previous studies should allow for a more accurate interpretation of remotely acquired data without the need for any scientist to actually stand on the Martian surface, a feat that is still many years away from us.'

How do we know a meteorite is from Mars?

Martian meteorite named Los Angeles. Natasha Stephen is investigating the composition of different meteorite minerals, shown here with false colours.
The main way scientists know a meteorite is from Mars is by looking at the trapped gases in glass pockets inside a meteorite, which match almost exactly the composition of Mars' atmosphere. 'We know the composition of Mars' atmosphere from data collected by NASA Viking missions in the 1970s,' explains Natasha.

Another way to identify a Martian meteorite is to analyse its oxygen isotopes - they are specific to regions of the solar system so each has its own 'signature'. Oxygen isotopes from Mars have a unique Martian signature.

'Martian meteorites are also typically younger than other stony meteorites,' says Natasha. 'They have travelled a shorter distance since ejection off the host’s surface'.

Why is it important to understand Mars?

Mars is our closest neighbour and many of its rocks are similar to Earth's. It once had active volcanoes but at some point Mars stopped being geologically active. Scientists would like to know why, and whether this could be the future for Earth.

Also, we know that there was water on Mars and inactive volcanoes show there was once energy. Water and energy are two necessities for life. So, was there ever life on Mars? Or could there be in the future?

With Tissint and other Martian meteorites such as the 13 looked after at the Museum, as well as NASA's Curiosity rover that lands on the surface of Mars a week from today, scientists will be able to get much closer to answering these questions.

Fonte: Natural History Museum

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