A series of studies published last week in the journals Science and Science Advances offer a new, detailed look at the makeup of a small asteroid called Bennu. The studies come just before NASA’s OSIRIS-REx spacecraft plans to pick up a sample from the asteroid’s surface on October 20 and return with it to Earth in 2023.
Before the OSIRIS-REx spacecraft reached the asteroid in 2018, astronomers could only study it with telescopes that couldn’t make out details smaller than cities or states, Michael Greshko reports for National Geographic. OSIRIS-REx allows astronomers to map details the size of basketball courts, sheets of paper and postage stamps, depending on the imaging tool they used.
"The reason there’s so much interest in asteroids is a lot of them are very primitive, from when the Solar System formed, and they didn't change with wind and water, or weather like on Earth," planetary scientist Amy Simon of NASA’s Goddard Space Flight Center tells Passant Rabie at Inverse. "They're still more pristine than anything you could find in the universe."
Researchers chose Bennu for close study and a sample-return mission because it is a relatively rare type of asteroid that’s rich in carbon-containing molecules, or organics, and because it formed early in the history of our solar system, Neel Patel reports for the MIT Technology Review. It’s also relatively close to Earth.
Bennu is about a third of a mile wide, made of a pile of rubble that is loosely held together by its own gravity, per National Geographic. The rubble resulted from a collision with a 60-mile-wide object in the asteroid belt that destroyed Bennu’s parent body, a larger asteroid. Bennu probably formed between 700 million and two billion years ago somewhere between Mars and Jupiter, and has drifted closer to Earth since then.
Measurements of the way that infrared light reflects off of Bennu’s surface revealed that about 98 percent the asteroid’s surface is coated in carbon-containing, organic molecules. And bright veins, narrow but about three feet long, suggest that water flowed on Bennu’s parent body, per the Technology Review. However, the surface of an asteroid has a poor chance of hosting early life.
“You’re in the vacuum of space, there’s no atmosphere, you’re looking at a lot of irradiation, it’s cold – you wouldn’t want to sit on the surface,” says Goddard Space Flight Center planetary scientist Hannah Kaplan to Leah Crane at New Scientist. “It’s not a favorable environment per se, but it does have a lot of the factors that make a place technically habitable.”
The OSIRIS-REx mission is investigating whether fragments of an object like Bennu’s parent body may have carried organic molecules, the basic ingredients for life, to Earth. A meteorite carrying organic molecules could have ferried them through Earth’s atmosphere to the chemical soup where life eventually evolved.
"Every day we have stuff raining down that we don’t see," Simon tells Inverse. "But early on in the Solar System, there would’ve been a lot more of these collisions."
On October 20, OSIRIS-REx will make a touch-and-go sampling attempt at a site on Bennu called Nightingale. (Several regions of the asteroid are named for birds.) Many boulders at the Nightingale site, including a three-story-high boulder nicknamed Mt. Doom, seem to hold a lot of organic molecules.
And a study of weathering of the asteroid by solar winds and micrometeorite strikes found that Nightingale is one of the least-weathered, best-preserved parts of the asteroid, per Technology Review. So the sample of at least 60 grams of asteroid material could give insight into activity in the solar system billions of years ago.
“This is why we do spacecraft exploration,” Kaplan tells National Geographic. “We didn’t expect to see these things, we cannot see them from Earth, and we needed to be orbiting pretty close up to the asteroid in order to see them.”