spaceSpace and Physics

OSIRIS-REx Leaking Asteroid Sample After Slightly Too Enthusiastic Bennu Touchdown


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer


OSIRIS-REx may have bitten off more of asteroid Bennu than it can chew. NASA/Goddard/University of Arizona

On October 20, NASA spacecraft OSIRIS-REx grabbed a sample of the carbonaceous asteroid Bennu to bring back to Earth for analysis. However, it seems the plucky probe was a bit too eager to do its job, grabbing so much of Bennu its collector couldn't close, leaving a trail of asteroid dust in its wake. How much this will affect the mission remains to be seen, but success is not as certain as it looked earlier in the week.

OSIRIS-Rex’s key goal was to snatch at least 60 grams (2 ounces) from Bennu’s surface and bring it home. In the space of a brief touchdown, there’s no opportunity for precision weighing. Combined with the fact that plenty of planetary scientists would love more material to analyze, the mission was programmed to err on the side of taking more asteroid.


But err it may have. Images of the sample collector show particles apparently escaping from its head. The mission team suspects so much material was taken larger rocks have wedged open the mylar flat that was meant to serve as the collector’s lid, allowing smaller grains to escape into space.

This series of three images shows some of the asteroid samples escaping from OSIRIS-Rex’s Touch-and-Go Sample Acquisition Mechanism (TAGSAM) sampler head, which is slightly wedged open. NASA/Goddard/University of Arizona

With the collector apparently holding much more than 60 grams, there is room for some to be lost while still returning at least the hoped-for quantity. On the other hand, since it seems the lid can’t be shut properly the precious cargo is likely to continue leaking. The question is: how much? “Time is of the essence," Zurbuchen said.

It's estimated at least half an ounce of particles were visible outside the sampler in images taken as it backed away from Bennu. "We're almost a victim of our own success here," mission lead scientist Professor Dante Lauretta of the University of Arizona, said. 

OSIRIS-Rex will not have an opportunity to start the journey back to Earth until March, and won’t reach home before September 2023. However, long before that happens the slice of Bennu is to be placed inside a return capsule, which will hopefully stop the leakage.


The best that can be done is hasten the safe storage inside the return capsule, with the team now aiming to do this by Tuesday, October 27. In the meantime, all efforts are being made to minimize any disturbance that might jar more material loose. Plans to spin the spacecraft in order to measure the sample’s weight have been abandoned, as has the possibility of taking a second 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.”

A lesser problem is that even if OSIRIS-REx returns with the desired quantity, the loss of dust-sized particles while larger rocks were captured may make the sample not as representative of Bennu's surface as anticipated.

Despite this, NASA’s Dr Thomas Zurbuchen struck a positive note in a statement. “Although we may have to move more quickly to stow the sample, it’s not a bad problem to have," he said. "We are so excited to see what appears to be an abundant sample that will inspire science for decades beyond this historic moment.”

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