NASA’s OSIRIS-REX Mission Touched Bennu Asteroid. How Much Will It Bring Home?

NASA's OSIRIS-REX Mission Touched Bennu Asteroid. How Much Will It Bring Home?


When NASA’s OSIRIS-REX spacecraft touched the surface of an asteroid on Tuesday to gather a sample of rocks and dirt, the operation proceeded smoothly, to the glee of the mission’s operators.

“Transcendental,” Dante Lauretta, the principal investigator of the mission, said moments later. “I mean, I can’t believe we actually pulled this off.”

But the biggest question remained unanswered: How much of the asteroid did OSIRIS-REX pick up? Did it manage to gather any samples at all?

With the asteroid — a rock named Bennu that is roughly as wide as the Empire State Building is tall — exerting only a wisp of gravitational pull, it was not possible to simply put the sampling container on a scale and weigh it.

In addition, the spacecraft could not send back much data as it swooped in for its collection attempt. It was on the other side of the solar system, more than 200 million miles from Earth, and as it descended toward the asteroid, its main antenna was not pointed at our planet. That meant OSIRIS-REX could provide only rudimentary “bread crumbs” telling mission controllers of its position, velocity and status, but not photos of the asteroid that would reveal the spot that the spacecraft touched.

The scientists chose a target they named Nightingale, located within a crater near Bennu’s north pole.

After gathering the sample, the spacecraft backed away from the asteroid and returned to a higher orbit. From there, it could start beaming back to Earth the reams of data it had collected.

NASA is scheduled to release some of the photos at a news conference on Wednesday at 5 p.m. The news conference will be broadcast on NASA Television.

Those pictures should provide more clues, but the scientists still will not determine how much material is trapped within the sample collector, which resembles an automobile air filter, until Saturday.

“There’s an incredibly clever physics experiment that the team has designed here called the sample mass measurement,” Dr. Lauretta said during the NASA Television broadcast on Tuesday.

The robotic arm with the sample collector at the end will be extended and then the spacecraft will be nudged into a spin on Saturday. “We’re measuring a property called the moment of inertia,” Dr. Lauretta said.

The scientists will compare the rate of spin to what they measured before collecting a sample. Just as a skater with outstretched arms holding a barbell would spin slower than a skater holding nothing, OSIRIS-REX will spin slower depending on how much material was picked up.

Scientists are hoping for at least a couple of ounces, but it could be more than four pounds.

“The precision, just like everything on this program, is phenomenal,” Dr. Lauretta said. “We’re talking tens of grams of precision on a measurement on a spacecraft hundreds of millions of miles away.”

If by unlucky chance OSIRIS-REX came up empty on Tuesday, it can try two more times.

The collection of the asteroid sample is the climax of the $800 million mission, which launched four years ago. The spacecraft has been making detailed observations of Bennu for two years, mapping features of its surface as small as a couple of inches wide. It even discovered that Bennu was shooting debris from its surface into space.

Asteroids, mostly located in orbits between Mars and Jupiter, are bits that never coalesced into a planet, and planetary scientists hope that the samples from Bennu could shed light on what the young solar system was like when it formed 4.5 billion years ago. Asteroids like Bennu, which possesses carbon-rich minerals, may have provided the building blocks for life to arise on Earth.

The asteroid is also being studied because its orbit could cause it to collide with Earth late in the 22nd century. The likelihood of such an occurrence is low, and the asteroid is not large enough to end human civilization should it occur.

OSIRIS-REX — the name is a shortening of Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — is to leave the asteroid next year and drop off the sample, which will parachute to a landing in Utah on Sept. 24, 2023.


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