Bennu is a near-Earth asteroid currently being orbited by NASA’s OSIRIS-REx mission. And in October, the spacecraft will play the asteroid “tag”, collect samples from the surface and return them to Earth by 2023.
While many asteroids seem dull and lifeless, it is surprisingly active. And it cannot be alone.
The first detailed images of the spacecraft showed that Benue is a junk-pile asteroid shaped like a spinning top and boulder-covered, not all of them expecting a smooth asteroid. Debris-piles are asteroids literally piles of rocks held together by gravity.
Shortly after OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer) arrived in Benue, the spacecraft’s cameras captured something more unexpected.
The asteroid was releasing small plums of material into space – mainly small pebbles, and on a regular basis.
“We thought Beanu was a wild card discovery in a boulder-covered surface asteroid, but these particle events certainly surprised us,” OSIRIS-REX’s chief investigator and a professor at the University of Arizona said in a statement .
“We have spent the last year investigating the active surface of Benue, and it provides us with a remarkable opportunity to expand our knowledge of how active asteroids behave.”
At first, the researchers did not realize that Benue was launching small pebbles into space.
But the mission’s leading astronomer and scientist Karl Herrengröther of the University of Arizona’s Lunar and Planetary Laboratory closely considered the images captured by OSIRIS-REX. They were taken just days after the spacecraft made its first up-close encounter with the asteroid.
After launching in 2016, OSIRIS-REX used wires to help it reach the asteroid. Its navigation camera portrays stars in the background, which are compared with the star chart to keep it on track.
Hergenrother was analyzing images sent back by the spacecraft when she realized that the asteroid was surrounded by too many stars.
“I was looking at the star pattern in these pictures and thought, ‘Huh, I don’t remember that star cluster,” Hergenother, an author on the study archive, also said in a statement.
“I only noticed this because there were 200 points of light where there should be about 10 stars. Also, it was just a dense part of the sky.”
It turned out that they were not stars. Those points of light represented clouds of particles ejected from the asteroid’s surface.
Asymmetries of bennu
Since OSIRIS-REX began observing Benue’s unusual behavior, the spacecraft has seen more than 300 particle rejection events. But they are not all the same.
Sometimes, particles are ejected with enough force to escape into space. Orbit a short distance around other asteroids. And many particles fall back on the asteroid.
The majority of this activity occurs during the two-hour afternoon to evening time period on the asteroid.
These events have been observed by the “eyes” of the spacecraft, or navigation camera suits that look for fugitive particles around the genu. The observations helped the scientists to realize that Bennu regularly discharges material.
But these particles, the largest of which is about 2 inches in diameter, do not pose a threat to the spacecraft. Benue’s weak gravity means that the particles are moving slower than the spacecraft.
“Space is so empty that even when the asteroid is throwing hundreds of particles, as we’ve seen in some events, the probability of one of the spacecraft colliding is extremely small,” Hergenother said. “And even if it was going to happen, most of them don’t accelerate or get bigger due to the damage.”
Between January and September 2019, scientists studied about 668 particles, which separated from Benue. They measured between 0.2 and 0.4 inches and moved only 8 inches per second or the equivalent of a beetle growing above the ground. The fastest reached 9.8 feet per second, but there was only one example of this.
This occurs on average, with an average of one or two particles being ejected from the asteroid each day, most of which return to the asteroid. This means that Benu is not losing much.
“To give you an idea, during the first event after arrival we saw 200 particles that fit on a 4-inch x 4-inch tile,” he said. “The fact that we can even see them is a testament to the capabilities of our cameras.”
what causes it?
To understand the reason behind these particle dust-ups, scientists investigated the possible release of water vapor on the asteroid, the effects of small meteorites or rocks breaking on the surface.
Bennu completes a detour every 4.3 hours, exposing the boulder on the asteroid to continuously heat daytime and nighttime cooling. This will cause rocks to break and break over time, causing their particles to flow into space.
It is also possible that small rocks like meteorites hit the asteroid in the afternoon, kicking off the asteroid’s contents in space.
Given the fact that most activity was observed during the afternoon when the rocks are experiencing heat either these are either strong or likely. Based on the asteroid’s gravity, there is not much to disturb its surface.
However, more comments are needed to be sure. But the particles detected information about the gravity of the asteroid that the spacecraft would only know when it got too close – dangerously close – to the asteroid.
Senior author and senior research expert Steve Chesley of one of the studies said, “The particles were an unexpected gift to the science of gravity at Benue because they allowed us to see small changes in the asteroid’s gravitational field, about which we Would not have known otherwise. ” In a statement, at NASA’s Jet Propulsion Laboratory in Pasadena, California.
By tracking the trajectory of the particles, scientists noticed that some remained suspended around the asteroid for a few hours before landing again, while others are now orbiting the sun on their own.
Researchers also observed interesting events like a particle that orbited the asteroid for a week long, and others that went back into space after it hit the surface again.
“A particle came down, hit a boulder and went back to orbit,” Hergenother said. “If Bennu has this kind of activity, there is a good chance to do all the asteroids, and that’s really exciting.”
These findings have suggested why sending an astronaut to study an asteroid is so important, suggesting that these celestial bodies can be dynamic, active, and completely unpredictable.