NASA Finally Gets At Its Bits of Bennu

You might wonder why NASA (and scientists) care so much about stuff that looks like some black gravel. It's because it is likely the stuff that formed the solar system.

Rocky Planet iconRocky Planet
By Erik Klemetti
Jan 29, 2024 3:50 PMJan 29, 2024 3:54 PM
This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles (24 kilometers). The image was obtained at a 50° phase angle between the spacecraft, asteroid and the Sun, and in it, Bennu spans approximately 1,500 pixels in the camera’s field of view.
A mosaic image of asteroid Bennu. (Credit: OCAMS/NASA)


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Eight years. Over a billion dollars. New tools that even get at the samples ... and this is what people saw:

The sample tray from the return capsule of OSIRIS-REx. These dark black rocks are pieces of the asteroid Bennu. Credit: NASA.

If you're a cynic, you might say that's an awful lot for what looks like a plate full of black rocks. You could go out into your driveway and collect something that looks pretty similar to the sample container from NASA's OSIRIS-REx mission.

However, you'd be wrong. As they say, looks can be deceiving and the material brought back from the asteroid Bennu may be the stuff that our planet and ourselves were born. Bringing it back to Earth will open up entirely new avenues to study the early solar system along with the origins of life here and across the universe.

Bennu is what planetary geologists call a "B-type" asteroid. It is potentially made of the same material that coalesced into our solar system over 4.5 billion years ago. The material that makes up Bennu is full of organic compounds (meaning that they have complex CH molecules not that they were made by life) and water -- something we call "carbonaceous chondrites".

We have some meteorites such as the famous Allende meteorite from Mexico that are likely made of the same material as Bennu. However, unlike Bennu, these meteorites are not the same as what might have been around at the start of the solar system because they ended up landing on Earth. That whole process of crashing through our atmosphere and then sitting on the surface means that they have changed. It might be unnoticeable to many, but they are different from that primordial material that made the Earth.

The capsule containing pieces of Bennu retrieved by NASA's OSIRIS-REx mission sitting in the desert of Utah in September 2023. Credit: NASA.

That's where a mission like OSIRIS-REx comes in. It took years to catch up with Bennu, then put a lander on it to sample its weird, rocky surface, then send that sample back to Earth. The sample lay sealed in the capsule all the way back from Bennu, through Earth's atmosphere and all the way to the ground in Utah last fall. It even tried to keep its secrets longer that expected as the canister was closed so tightly that NASA had to develop and certify new tools to open it.

What was found inside was a dark, almost soot-looking material that likely has been orbiting the Sun for 4.5 billion years in the void of space. Bennu is tiny, only about half a kilometer along each axis making an oddly diamond-like shape (see the image at the top). The surface of the asteroid was much more rubbly than planetary geologists and astronomers expected, making it look more like a pile of rocks stuck together. Oddly, this was similar to Ryugu, another asteroid that the Japanese Space Agency sampled only a few years prior.

What makes the sample return so fascinating is that now we have nearly-pristine material from the early solar system and the ability to run an endless number of analyses on the materials. This would have been impossible without returning pieces of Bennu to Earth because you can't do most of these analyses on some robot spacecraft millions of miles away. The instruments might be too delicate or heavy or complicated to even conceive of running these analyses on the asteroid. This isn't like the USS Enterprise that can just "scan" the surface. We need to bring the sample to the instruments, not vice versa.

(NASA/Goddard Space Flight Center via AP) OSIRIS-REx collected a sample from the asteroid Bennu.

So, for only the second time (and first time for the US), we've brought material from an asteroid back to Earth. We can determine the precise age, chemical and isotopic composition, the minerals that formed and the (ideally) unchanged organic compounds that can be found when a solar system forms. Add the water we know is present in these asteroids and we have all the ingredients that lead to life on Earth (albeit a few billion years after Bennu formed).

These chunks found on an asteroid millions of kilometers from Earth are our humble beginnings. Now we have the opportunity to discover some of the primordial secrets of the formation of the Earth. All this from a tray of black rocks.

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