A small piece of rock will be hurled into space this week on one of the strangest interplanetary voyages ever attempted. A tiny piece of Martian basalt the size of a 10p coin will be launched on board a US robot probe on Thursday and propelled towards the red planet on a seven-month journey to its home world.

This extraordinary odyssey, the interplanetary equivalent of sending coals to Newcastle, will form a key part of Nasas forthcoming Mars 2020 expedition. Space engineers say the rock which has been donated by the Natural History Museum in London will be used to calibrate detectors on board the robot rover Perseverance after it lands and begins its search for signs of past life on the planet.

Some of the Martian meteorites we have are very fragile, but we chose this one specifically because its as tough as old boots

When you turn on instruments and begin to tune them up before using them for research, you calibrate them on materials that are going to be like the unknown substances you are about to study. So what better for studying rocks on Mars than a lump that originated there? said Professor Caroline Smith, the Natural History Museums curator of meteorites.

Scientists were confident that the rock they were returning to Mars originated on the planet, added Smith, who is also a member of the Mars 2020 science team. Tiny bubbles of gas trapped inside that meteorite have exactly the same composition as the atmosphere of Mars, so we know our rock came from there.

It is thought that the Martian meteorite was created when an asteroid or comet plunged into the planet about 600,000 to 700,000 years ago, spraying debris into space. One of those pieces of rubble swept across the solar system and eventually crashed on to Earth. That meteorite now known as SAU 008 was discovered in Oman in 1999 and has been in the care of the Natural History Museum since then.

Among the instruments fitted to the Perseverance rover is a high-precision laser called Sherloc, which will be used to decipher the chemical composition of rocks and determine if they might contain organic materials that indicate life once existed or still exists on Mars. The inclusion of a piece of SAU 008 is intended to ensure this is done with maximum accuracy.

The piece of rock we are sending was specifically chosen because it is the right material in terms of chemistry, but also it is a very tough rock, added Smith. Some of the Martian meteorites we have are very fragile. This meteorite is as tough as old boots.

Once Perseverance has selected the most promising rocks it can find, it will dump them in caches on the Martian surface. These will then be retrieved by subsequent robot missions and blasted into space towards Earth for analysis.

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Rock from Mars heads home after 600,000 years on Earth - The Guardian