It is this curiously shaped asteroid in particular that could hold clues to the ultimate origin of life, which is why NASA’s 2016 probe OSIRIS-REx sent to Bennu to take soil samples. Bennu is part of a group of asteroids known to contain carbonaceous organic molecules – ingredients essential to life as we know it on Earth – as well as minerals that have been altered solely by the action of water. Researchers believe that at least some of the water and organic molecules on our home planet come from asteroids, so objects like Bennu may have supplied Earth with the chemicals it needs for life.
In addition, Bennu is a potential danger to the earth. Its orbit around the sun crosses that of our planet and there is a roughly one in 2,700 chance that it could impact Earth by the end of the 22nd century, making careful research into this lump of rock all the more important.
While many of the boulders that make up Bennu come from the early days of the solar system, Bennu itself is the product of more recent chaos. Researchers think that about a billion years ago, a celestial body about 100 kilometers across in the asteroid belt was destroyed by a massive impact. This resulted in large amounts of debris, which resulted in a group of smaller asteroids, including Bennu.
When the original celestial body was very young, it had enough internal heat to hold water in liquid form in its soil. As this water seeped through cracks, carbon minerals were deposited there over the millennia. While Bennu was built from debris of the great asteroid by gravity, these primal veins remained intact in the large boulders now scattered across Bennu’s surface.
The largest carbon vein produced to date OSIRIS-REx is about three feet long. The length and thickness of these veins indicate that the great asteroid from which Bennu originated must have exhibited significant hydrothermal activity for thousands, if not millions, of years.
“That’s why we’re exploring space with probes,” says Hannah Kaplan, planetologist at NASA’s Goddard Space Flight Center, a member of the OSIRIS-RExteam and one of the authors of the new studies. “We didn’t expect to find this and we can’t see it from Earth, so we had to fly around the asteroid pretty close to see it.”
The carbon veins then came to light OSIRIS-REx amassed an enormous amount of high-resolution data. Rivkin says that one of the instruments on board the spacecraft studies the composition of Bennu’s surface, with a resolution that distinguishes objects the size of a basketball court. Another instrument maps color variations in the terrain on Bennu, with a distinctive character of a sheet of A4. And with a third instrument, the observing scientists are even able to spot objects the size of a postage stamp on Bennu’s surface.
Strange space rock
Bennu is a porous “mess” loosely held together by the very low gravity of the celestial body, which is eight million times less strong than that on Earth. That makes exploring this strange world an adventure in that Alice in Wonderland wouldn’t look out of place.
Since OSIRIS-REx orbiting the asteroid, the probe has observed unexpected details. For example, bizarre ‘popcorn rocks’ have been observed launching themselves from the surface of Bennu, probably as a result of warming from the sun. Among the tarmac-colored boulders on Bennu, the spacecraft has even spotted fragments of another asteroid, Vesta. The probe succeeded recognize the chemical signal of the mineral mix on Vesta.