Bennu is a near-Earth asteroid that is presently being orbited by NASA’s OSIRIS-REx mission. And in October, the spacecraft will play “tag” the asteroid, gather samples from the floor and return them to Earth by 2023.
While many asteroids appear uninteresting and lifeless, this one is surprisingly energetic. And it may not be alone.
The spacecraft’s first detailed photographs revealed that Bennu is a rubble-pile asteroid formed like a spinning high and coated with boulders, by no means the sleek asteroid they anticipated. Rubble-pile asteroids are actually piles of rocks held collectively by gravity.
Shortly after the arrival of OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security — Regolith Explorer) at Bennu, the spacecraft’s cameras captured one thing else surprising.
The asteroid was releasing small plumes of fabric into house — primarily little pebbles, and regularly.
“We thought that Bennu’s boulder-covered surface was the wild card discovery at the asteroid, but these particle events definitely surprised us,” stated Dante Lauretta, the OSIRIS-REx principal investigator and a professor on the University of Arizona, in an announcement.
“We’ve spent the last year investigating Bennu’s active surface, and it’s provided us with a remarkable opportunity to expand our knowledge of how active asteroids behave.”
At first, researchers did not notice that Bennu was launching little pebbles into house.
But Carl Hergenrother, the mission’s lead astronomer and University of Arizona’s Lunar and Planetary Laboratory scientist, took a more in-depth have a look at the photographs captured by OSIRIS-REx. They had been taken simply days after the spacecraft arrived for its first up-close rendezvous with the asteroid.
OSIRIS-REx used stars to assist it attain the asteroid after launching in 2016. Its navigation digital camera photographs stars within the background, that are in contrast with star charts to maintain it on monitor.
Hergenrother was analyzing photographs despatched again by the spacecraft when he realized the asteroid was surrounded by too many stars.
“I was looking at the star patterns in these images and thought, ‘huh, I don’t remember that star cluster,'” Hergenrother, additionally an writer on the examine assortment, stated in an announcement.
“I only noticed it because there were 200 dots of light where there should be about 10 stars. Other than that, it looked to be just a dense part of the sky.”
It turned out that they weren’t stars in any respect. Those dots of sunshine represented clouds of particles ejected from the floor of the asteroid.
Since OSIRIS-REx started observing Bennu’s uncommon habits, the spacecraft has witnessed greater than 300 of those particle ejection occasions. But they are not all the identical.
Sometimes, the particles are ejected with sufficient drive to flee into house. Others orbit across the asteroid briefly. And most of the particles fall again onto the asteroid.
Much of this exercise occurs throughout a two-hour afternoon to night time interval on the asteroid.
These occasions have been witnessed by the spacecraft’s “eyes,” or the navigation digital camera suite that retains a lookout for runaway particles round Bennu. The observations helped scientists notice that Bennu sheds materials commonly.
But these particles, the most important of that are about 2 inches in diameter, do not pose a risk to the spacecraft. Bennu’s weak gravity implies that the particles are transferring in sluggish movement in comparison with the spacecraft.
“Space is so empty that even when the asteroid is throwing off hundreds of particles, as we have seen in some events, the chances of one of those hitting the spacecraft is extremely small,” Hergenrother stated. “And even if that were to happen, the vast majority of them are not fast or large enough to cause damage.”
Between January and September 2019, scientists studied about 668 particles that popped off of Bennu. They measured between 0.2 and 0.Four inches and solely moved about eight inches per second, or the equal of a beetle transferring over the bottom. The quickest reached 9.eight toes per second, however there was just one occasion of this.
This averaged out to 1 or two particles being ejected from the asteroid every day, with the vast majority of them returning to the asteroid. This means Bennu is not dropping a lot mass.
“To give you an idea, all of those 200 particles we observed during the first event after arrival would fit on a 4-inch x 4-inch tile,” he stated. “The fact that we can even see them is a testament to the capabilities of our cameras.”
What causes it?
To perceive the trigger behind these particle dust-ups, scientists investigated the doable launch of water vapor on the asteroid, impacts by tiny meteoroids or rocks cracking on the floor.
Bennu completes a rotation each 4.three hours, which consistently exposes boulders on the asteroid to day heating and night time cooling. This would trigger the rocks to crack and break down over time, flinging their particles out into house.
It’s additionally doable that small rocks like meteoroids are putting the asteroid within the afternoon, which might kick materials on the asteroid out into house.
Given the truth that essentially the most exercise was seen in the course of the afternoon when the rocks are experiencing heating suggests both or each of those are sturdy potentialities. Based on the gravity of the asteroid, it would not take a lot to disturb its floor.
However, extra observations are wanted to know for certain. But the particles revealed details about the asteroid’s gravity that the spacecraft would solely know if it obtained too shut — dangerously shut — to the asteroid.
“The particles were an unexpected gift for gravity science at Bennu since they allowed us to see tiny variations in the asteroid’s gravity field that we would not have known about otherwise,” stated Steve Chesley, lead writer of one of many research and senior analysis scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, in an announcement.
By monitoring the trajectories of the particles, the scientists seen that some remained suspended across the asteroid for a couple of hours earlier than touchdown once more, whereas others are actually orbiting the solar on their very own.
The researchers additionally witnessed attention-grabbing occasions like one particle that orbited the asteroid for so long as every week, and others that ricocheted again into house after they hit the floor once more.
“One particle came down, hit a boulder and went back into orbit,” Hergenrother stated. “If Bennu has this kind of activity, then there is a good chance all asteroids do, and that is really exciting.”
These findings have steered why it is so necessary to ship a spacecraft to review an asteroid, which is revealing that these celestial our bodies may be dynamic, energetic and fully surprising.