A piece of Mars that fell to Earth as a meteorite after being blasted away from the red planet during an ancient asteroid impact will be flown home courtesy of NASA. And London’s Natural History Museum.

The U.S. space agency plans to mount a chunk of the meteorite, known as Sayh al Uhaymir 008, or SaU008, on its Mars 2020 rover to serve as a calibration target for a high-precision laser instrument that can detect features as fine as a human hair. The instrument, the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals, or SHERLOC, will be the first on Mars to use spectroscopic analysis familiar to forensics experts to detect carbon-based chemicals – the building blocks of life as it is known on Earth.

But the instrument’s high precision requires careful calibration.

“We’re studying things on such a fine scale that slight misalignments, caused by changes in temperature or even the rover settling into sand, can require us to correct our aim,” said Luther Beegle, the SHERLOC principal investigator at NASA’s Jet Propulsion Laboratory. “By studying how the instrument sees a fixed target, we can understand how it will see a piece of the Martian surface.”

Instruments on previous spacecraft used calibration targets made of metal, glass, rock slices and other materials, but the SHERLOC team came up with a different solution: using a piece of Mars as a more realistic target.

Only about 200 verified martian meteorites have been found on Earth. To select the best candidate for the SHERLOC instrument, one that would exhibit the desired chemical signatures, the JPL team turned to Caroline Smith, principal curator of meteorites at London’s Natural History Museum. She provided access to SaU008, which was found in Oman in 1999, allowing NASA to collect a sample.

“Every year, we provide hundreds of meteorite specimens to scientists all over the world for study,” Smith said. “This is a first for us: sending one of our samples back home for the benefit of science.”

NASA’s now-defunct Mars Global Surveyor spacecraft carried a fragment of a martian meteorite known as Zagami, but the SaU008 fragment will be the first to make a round trip back to the red planet’s surface.