In 1999, out on the gravel flats of central Oman, somebody picked up a darkish, unremarkable rock. It went into the Natural History Museum in London the next 12 months, catalogued as Sayh al Uhaymir 008, or SaU 008.
That rock is a fraction of Mars and as we speak a slice of it’s bolted to a rover driving round Jezero crater, doing a small, sensible job on the planet it was thrown off of a whole lot of 1000’s of years in the past.
The rock itself
SaU 008 is a shergottite, a kind of volcanic rock that makes up a lot of the Martian meteorites we now have on Earth. Scientists determine Martian meteorites by means of their rock and noble-gas chemistry and mineralogy, together with gases trapped in some specimens that match measurements of the Martian environment. The slice sent to Mars accommodates olivine, maskelynite and iron-magnesium pyroxenes, plus calcium-carbonate weathering options acquired throughout its keep within the Arabian desert.
Caroline Smith, then the Museum’s Principal Curator of Meteorites, put the selection plainly when the mortgage was introduced. The piece “was specifically chosen because it is the right material in terms of chemistry, but also it is a very tough rock.” Toughness issues greater than it sounds. Something going to Mars has to outlive launch and touchdown, and lots of attention-grabbing samples are too fragile for that. Smith’s shorthand for that is relatable: “This meteorite is as powerful as previous boots.”
The way it received right here, and the way it received again
The journey out was violent. An affect on Mars, thought to have occurred roughly 600,000 to 700,000 years ago, hit laborious sufficient to fling particles off the planet fully. A kind of fragments ultimately reached Earth, then sat within the Oman desert till it was present in 1999.
The journey dwelling was significantly extra organized. In 2018 the Mars 2020 group chosen a slice of SaU 008 for the rover, and Perseverance landed in Jezero crater on 18 February 2021. That made it the first Martian meteorite fragment returned to the planet’s surface. Smith didn’t oversell the second, however she didn’t undersell it both: “This is a first for us,” she mentioned, “sending considered one of our samples again dwelling for the advantage of science.”
Why a bit of Mars makes a superb calibration goal
The slice isn’t driving alongside as a memento. It’s considered one of ten targets on SHERLOC’s external calibration assembly. SHERLOC makes use of deep-ultraviolet Raman and fluorescence spectroscopy, along with imaging, to map minerals and natural compounds in Martian rocks. The opposite targets embrace optical requirements and samples of spacesuit supplies.
SaU 008 supplies one thing particularly helpful: a pure Martian pattern whose mineralogy and natural signatures had been characterised on Earth earlier than launch. That provides the group floor reality for checking how SHERLOC reads comparable supplies on Mars. Rohit Bhartia, SHERLOC’s deputy principal investigator, defined why the meteorite suited the job: “This kind of science requires texture and organic chemicals — two things that our target meteorite will provide.”
Repeated measurements additionally let the group examine whether or not the instrument’s response, or the uncovered pattern itself, modifications with time on Mars. Smith anticipated that finding out it throughout the mission “will help us to understand the chemical interactions between the Martian surface and its atmosphere.”
That has began to repay. A 2025 analysis in the Journal of Geophysical Research: Planets in contrast SHERLOC observations of SaU 008 over Perseverance’s first 1,000 sols with measurements made earlier than launch. The instrument repeatedly detected the identical Raman and fluorescence signatures in the identical places. For a calibration goal, boring and constant is strictly the end result you need.
A working software, not a monument
The symmetry that will get written up as if it had been the entire story goes like this: a rock leaves Mars, wanders by means of area, lands in a desert, will get catalogued in London, after which goes again.
Informed that approach it feels like a homecoming.
However it’s nearly the alternative. SaU 008 didn’t return to be reunited with something. It went again as a result of it was the precise materials and hard sufficient to make the journey, and now it sits on a rover serving as a recognized reference whereas an instrument reads Martian rocks. It’s doing an unusual job.
A bit of 1 planet spent a whole lot of 1000’s of years getting dwelling accidentally, and when it lastly arrived on function, we gave it a chore.
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