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OSIRIS-REx has collected an excessive amount of asteroid materials and now a few of it’s floating away

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NASA confirmed that the OSIRIS-REx mission captured enough material from the asteroid Bennu during its sampling attempt on Tuesday. In fact, the spacecraft's collection chamber is now too full to be completely closed, causing some of the material to drift off into space. "There's so much in there that the sample is now escaping," said Thomas Zurbuchen, NASA's Associate Science Administrator, on Friday.

What should happen: On Tuesday, OSIRIS-REx descended to the asteroid Bennu (the object it has been studying from orbit for nearly two years, more than 200 million miles from Earth) and picked up debris from the surface in a six-second touchdown before it flew 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 check how much was collected. This included observations of the sample collection chamber with on-board cameras as well as a spin maneuver planned for Saturday that would approximate the mass of the sample by measuring the moment of inertia.

What really happened: For the past few days, the onboard cameras showed that the collection chamber was losing particles that were floating into space. "A significant part of the sample is swimming away," said mission leader Dante Lauretta on Friday. It turned out that the sampling attempt took in too much material – possibly up to two kilograms, the upper limit of what OSIRIS-REx was designed for. About 400 grams seem to be visible from the cameras. The collection lid did not close properly and remains trapped by parts up to three centimeters in size, creating a centimeter-wide gap in which the material can escape.

It appears that when the OSIRIS-REx touched down on Bennu's surface, the collecting head was four to eight inches deep, which would explain how much material was recovered.

How bad is it? It is not terrible! It is obviously worrying that some material has been lost, but that loss was mainly due to some movement of the arm on Thursday (the material behaves like a liquid in weightlessness, so any movement causes the sample to swirl around and possibly out the arm flows out chamber). Lauretta estimates that up to 10 grams could have been lost so far. However, considering how much has been collected, this loss is relatively small. The arm has now been placed in a park position so that the material moves more slowly, which should minimize additional loss.

What's next? The mission waives the planned weighing procedure as a sling maneuver would undoubtedly lead to more material loss, and NASA is confident that there is far more than the originally targeted 60 grams. Instead, the mission is speeding up the stowing of the sample, which NASA expects to take place on Monday. After the sample has been safely stowed away, OSIRIS-REx will leave Bennu in March and bring the sample back to earth in 2023.

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Steven Gregory