On September 8th, NASA launched a spacecraft to a near-Earth asteroid named Bennu. Among that spacecraft’s five instruments is a student experiment that will use X-rays to help determine Bennu’s surface composition.
The student experiment developed by researchers and students at MIT and the Harvard-Smithsonian Center for Astrophysics (CfA) is called the Regolith X-Ray Imaging Spectrometer, or REXIS, and is the second student experiment to ever fly on a NASA interplanetary mission. REXIS is a $5 million project that involved nearly 50 undergraduate students from MIT and Harvard.
“With Harvard undergraduates, we designed a wide-field X-ray imaging instrument that was built by students at MIT,” says Harvard astronomer and Deputy Instrument Scientist Josh Grindlay.
According to instrument scientist and Harvard astronomer Jaesub Hong, a primary goal for REXIS was educating students.
The mission, called the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx), was launched from Cape Canaveral, Florida. After its two-year journey to Bennu, the spacecraft will spend almost two years making observations and measurements before collecting a surface sample and returning it to Earth.
REXIS will help the mission team select the sample site by characterizing the asteroid’s Bennu emits X-rays through a process known as fluorescence, in which X-rays from the sun make atoms on the asteroid’s surface glow at specific energies, depending on which chemical elements are present.
“REXIS can image enhanced patches of glowing elements like magnesium, silicon, or iron that are typical in chondrite-type asteroids,” says instrument scientist Branden Allen.
Bennu is about 1,600 feet across, about twice the height of Boston’s John Hancock Tower. REXIS will be able to resolve details about 18 feet across.
Like many asteroids, Bennu represents a relic from the solar system’s formation that formed as pieces of primitive material stuck together over time. This means that it can tell scientists about the history of our solar system. Asteroids like Bennu may have delivered water, carbon, and other substances crucial to life to the early Earth.
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