In the ultimate example of sending coals to Newcastle, NASA is sending a piece of Mars back to the Red Planet on the Mars 2020 rover mission. The space agency's including a meteorite that had its origin on Mars may seem odd, but the purpose is completely practical as the sample will act as a calibration target for one of the mission's main instruments.
Spending all the time, money, and labor needed to send a spacecraft to the surface of Mars is pointless if the instruments included on the lander don't send back an accurate account of what they see. For this reason, each Mars landing mission includes a set of calibration targets that serve the same purpose as a test pattern card does on Earth in making sure video equipment is properly adjusted.
An example of this is on the Curiosity rover, which has a calibration palette consisting of a US 1909 penny for adjusting the sharpness of the rover's camera, color chips, a metric standardized bar graphic, and a stair-step pattern for depth calibration. Mars 2020 will carry a similar palette, but it will also include a fragment of the meteor Sayh al Uhaymir 008 (SaU008) for adjusting a high-precision laser on the rover's arm.
The laser, called the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC), is designed to illuminate features on rock samples as fine as a human hair and analyze them using Raman and fluorescence spectroscopies. To achieve the necessary precision, NASA engineers want to use a calibration sample that is as near to the Martian rocks as possible, so they reasoned that the best choice would be an actual piece of Mars that was blasted off the planet in an ancient asteroid strike and landed on Earth millions of years ago.
"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 of the Jet Propulsion Laboratory in Pasadena, California. "By studying how the instrument sees a fixed target, we can understand how it will see a piece of the Martian surface."
According to NASA, the idea behind SHERLOC is to use the laser to cause carbon-based compounds to fluoresce in a manner similar to that produced by a conventional UV lamp, and then examine the resulting spectrogram for signs of life. The meteor sample will help the instrument to better pick out the texture and organic chemicals found.
One of only 200 confirmed Martian meteorites found on Earth, Sayh al Uhaymir 008 was provided by the National History Museum in London and was selected because it not only provides good calibration characteristics, but is also robust enough to survive the journey from Earth to Mars without damage.
However, NASA says that this is not the first bit of Mars that it has sent home. The first was onboard the now inactive Mars Global Surveyor, which carries a chunk of a meteorite known as Zagami, but that is still in orbit around the planet. Meanwhile, another instrument on Mars 2020, the SuperCam, will have its own Martian meteorite calibration target. In addition, the rover will carry samples of materials that could be used in spacesuits and other equipment on future manned Mars expeditions.
"The SHERLOC instrument is a valuable opportunity to prepare for human spaceflight as well as to perform fundamental scientific investigations of the Martian surface," said Marc Fries, a SHERLOC co-investigator. "It gives us a convenient way to test material that will keep future astronauts safe when they get to Mars."
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