As the canister was moved during the stowage steps, some more of the sample floated away. Dr. Lauretta estimated that tens of grams were lost.
“We’ve come to realize that the particle loss, which continued throughout the entire stow, was what I would call a saltshaker effect,” Dr. Lauretta said. “It’s sloshing around as a result of that and a few of the particles, a small fraction of the collected sample, is escaping.”
After the canister was lowered into place, the top of the return capsule swung down like a clamshell and was held closed by two latches, sealing the sample container inside and preventing the loss of any more material.
Along the way, Dr. Lauretta said visual inspection of the collection canister confirmed there was about 400 grams, or close to a pound, of material inside. But the camera could peer into only about 17 percent of the volume of the collector, so it is possible that much more mass lies within.
The mission aimed to bring back a minimum of 60 grams, or just over 2 ounces of the asteroid.
The operation, which took about 36 hours, was completed on Wednesday. Because OSIRIS-REX is so far away, confirmation of each command sent to the spacecraft took 37 minutes — the time for light to travel there and back.
“As you can imagine, in the mission support area, everyone’s completed every one of these steps, there was cheering,” said Sandra Freund, the mission operations manager at Lockheed Martin Space in Colorado. “The best cheering event of them all was here at the end.”
Dr. Lauretta said that the escaping particles did offer some unexpected science. One of the surprising discoveries during OSIRIS-REX’s visit is that particles erupt off the surface of Bennu into space. “The properties that we inferred of those particles are very similar to what we’re seeing escaping,” Dr. Lauretta said. “It looks like you dumped a box of cornflakes out in space, and they’re fluttering around kind of in random motion.”