NASA touches an asteroid: What to know about OSIRIS-REx mission

Spacecraft touches down on asteroid Bennu

Tuesday evening marked another NASA milestone: A spacecraft called OSIRIS-REx touched an asteroid, called Bennu, and collected a sample for return to Earth!

Tuesday evening marked another NASA milestone: A spacecraft called OSIRIS-REx touched an asteroid, called Bennu, and collected a sample for return to Earth! 

What made this accomplishment so difficult is that, due to the delay in the time it takes for communication to and from the spacecraft and Earth, OSIRIS-REx had to use artificial intelligence to essentially determine by itself if it was safe to do the maneuver.  Over the past year, OSIRIS-REx has been orbiting Bennu and taking increasingly detailed images to find a site.  When the mission was originally developed, it was assumed that Bennu would be mostly smooth, with lots of regolith (“dirt”) and perhaps some rocks. 

What they found when OSIRIS-REx got there was a heavenly body littered with rocks and boulders.  So finding a site for the touch and go (“TAG”) became quite a challenge. Mission scientists finally chose a primary site, which they named Nightingdale, and three backup sites, called Osprey, Sandpiper and Kingfisher (somebody on the mission team must be a bird watcher). But as you’ll see in the video of my report, even Nightindale has a lot of rocks and boulders.

So, as OSIRIS-REx slowly lowered itself, it took a series of images and had to make its own decisions as to if it was safe for the TAG, which included proximity to boulders nearby (remember that the spacecraft was also slowly moving laterally to match Bennu’s rotation. I watched live as this unfolded, and the NASA person keeping us updated said that OSIRIS-REx was within one-half of a meter (about a foot-and-a-half) of it’s intended TAG location. Now THAT’S what I call precision! Had OSIRIS-REx determined that it was in danger of any contact with a large rock or boulder, it would have independently decided to abort and rise back up for another attempt at some point.

How did it collect the sample? When the TAGSAM head touched the surface, a cartridge of nitrogen fired and blew regolith and perhaps some pebbles into a collector in the TAGSAM head. All of this occurred in only five seconds, before OSIRIS-REx lifted back up.

How does NASA know if they collected enough material to return to Earth? This is pretty cool science:  once back in orbit around Bennu, OSIRIS-REx will extend the TAGSAM arm laterally out to the side of the spacecraft and spin the spacecraft. By doing this, they will compare the spacecraft’s moment of inertia of the arm empty (which they already know) versus with the sample, and this tells them how much sample they collected. If they don’t have enough, they can make two more attempts to collect additional samples, as they have enough nitrogen for three attempts. 

The goal is to bring back 2 to 70 ounces of pristine asteroid material. A lot of “out of the box” thinking went into this mission!

Once NASA has determined that they have enough sample to bring back, OSIRIS-REx will remain at Bennu until the asteroid is in the proper position for the spacecraft to begin its return to Earth.  In 2023, it will jettison a capsule with the sample, which will parachute down to a site in Utah on September 24th. At least 75 percent of the sample will be preserved for further research by scientists worldwide, and in the future.

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Why is this mission so important? 

Because, like comets, asteroids are chunks of “stuff” left over from the beginning of our solar system. Bennu likely broke off from a much larger carbon-rich asteroid about 700 million to 2 billion years ago. It likely formed in the Main Asteroid Belt between Mars and Jupiter, and has drifted much closer to Earth since then. Because its materials are so old, Bennu may contain organic molecules similar to those that could have been involved with the start of life on Earth. By learning more about Bennu, we learn more about ourselves!

More importantly (to many of you) is that asteroids periodically come close to -- and even hit --Earth. You may already know that it’s strongly suspected that a massive asteroid impact caused a severe and rapid global cooling that wiped out the dinosaurs and allowed mammals to flourish (good for us, I guess, because we evolved from those mammals -- although an asteroid impact today wouldn’t be such good news). 

Learning about these asteroids' density helps scientists develop technology to perhaps deflect an approaching asteroid headed our way. 

And by the way, Bennu has a 1-in-2,700 chance of hitting Earth during one of its close passes by in the late 22nd century.

About the Author:

Local 4 meteorologist Paul Gross was born in Detroit and has spent his entire life and career right here in southeast Michigan. Paul has researched, written and produced eight half-hour documentaries for WDIV, as well as many science, historical and environmental stories.