NASA collected a sample from asteroid Bennu, but some of it is leaking into space

The historic collection of a sample from the near-Earth asteroid Bennu by NASA’s OSIRIS-REx spacecraft on Tuesday was almost too successful.



a clock on the side: The spacecraft's sample head is full of rocks and dust collected from the surface of the asteroid Bennu. But some of the particles are slowly escaping through small gaps.


© NASA
The spacecraft’s sample head is full of rocks and dust collected from the surface of the asteroid Bennu. But some of the particles are slowly escaping through small gaps.

Some of the sample is leaking into space, according to Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson during a NASA press conference Friday.

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“The big concern now is that particles are escaping because we’re almost a victim of our own success,” he said. “Large particles left the flap open. Particles are diffusing out into space. They aren’t moving fast, but nonetheless, it’s valuable scientific material.”

The mission team analyzed images Thursday taken of the collector head of the spacecraft that showed that a substantial sample was collected — but there is so much material in the head that the flap designed to keep the sample inside is jammed.

This is allowing particles to escape into space. The mission team is changing the course of the events planned for the spacecraft this weekend and planning to stow the sample as quickly as possible so little material is lost. The researchers estimated that it’s continually losing between 5 to 10 grams of material. This flaky material floats in what resembles a cloud of particles around the head.

But the team isn’t sure of the exact loss rate because it’s not steady.

The mission was required to collect at least 2 ounces, or 60 grams, of the asteroid’s surface material. Based on the images they analyzed, the researchers are confident that the collector head on the end of the spacecraft’s robotic arm actually captured 400 grams of material. And that’s only what’s visible to them through the perspective of the camera.

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But particles are escaping through small gaps where a Mylar flap, or lid, is being held open by at least a centimeter by large rocks. And the activities planned for the spacecraft this weekend could cause more sample loss due to movement.

Previously, OSIRIS-Rex was expected to conduct a braking burn on Friday and a measurement of the sample’s mass on Saturday. Although this means the team won’t know the true mass of the sample until it returns to Earth in 2023, the mission team is confident that it will have a sufficient sample.

“We are working to keep up with our own success here, and my job is to safely return as large a sample of Bennu as possible,” Lauretta said. “The loss of mass is of concern to me, so I’m strongly encouraging the team to stow this precious sample as quickly as possible.”

The team will go through another evaluation process this weekend to ensure that the sample head could be stowed in the sample return capsule

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OSIRIS-REx collected too much asteroid material that it’s now floating away

NASA confirmed that the OSIRIS-REx mission picked up enough material from asteroid Bennu during its sample collection attempt on Tuesday. In fact, the spacecraft’s collection chamber is now too full to close all the way, leading some of the material to drift off into space. “There’s so much in there that the sample is now escaping,” Thomas Zurbuchen, NASA’s associate administrator for science, said Friday.

What was supposed to happen: On Tuesday, OSIRIS-REx descended to asteroid Bennu (the object it has studied from orbit for almost two years now, more than 200 million miles from Earth) and scooped up rubble from the surface during a six-second touchdown before flying back into space. 

The goal was to safely collect at least 60 grams of material, and the agency expected to run a series of procedures to verify how much mass was collected. Those included observing the sample collection chamber using onboard cameras, as well as a spin maneuver scheduled for Saturday that would approximate the sample’s mass through moment-of-inertia measurements. 

What actually happened: Over the last few days, the onboard cameras revealed that the collection chamber was losing particles that were floating into space. “A substantial amount of the sample is seen floating away,” mission lead Dante Lauretta said Friday. As it turned out, the sample collection attempt picked up too much material—possibly up to two kilograms, the upper limit of what OSIRIS-REx was designed to collect. About 400 grams of material seem visible from the cameras. The collection lid has failed to close properly, and remains wedged open by pieces that are up to three centimeters in size, creating a centimeter-wide gap for material to escape through.

It seems when OSIRIS-REx touched down on Bennu’s surface, the collection head went 24 to 48 centimeters deep, which would explain how it recovered so much material. 

How bad is it: It’s not terrible! It’s obviously concerning that some material has been lost, but this loss was mostly due to some movements of the arm on Thursday (the material behaves like a fluid in microgravity, so any movement will cause the sample to swirl around and potentially flow out of the chamber). Lauretta estimates that as many as 10 grams may have been lost so far. Given how much sample was collected, however, this loss is relatively small. The arm has now been moved into a “park” position so that material is moving around more slowly, which should minimize additional loss.  

What’s next: The mission is forgoing the scheduled weigh procedure, since a spin maneuver would undoubtedly lead to more material loss, and NASA is confident it has way more than the 60 grams the agency initially sought. Instead, the mission is expediting the stowing of the sample, which NASA expects to take place Monday. After the sample is stowed safely, OSIRIS-REx will leave Bennu in March, and bring the sample back to Earth in 2023.

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