HOUSTON – Asteroid Bennu, with the shape of a spinning top, proves to be extremely robust. It will make it difficult for a NASA spacecraft, Osiris-Rex, to vacuum up a sample to take back to Earth. It was designed to collect sand and gravel, not boulders.
In addition, Bennu shoots back.
"We see that Bennu regularly delivers material to outer space," says Dante Lauretta, Osiris- Rex's principal researcher during a conference call on Tuesday. He and other mission researchers have presented their findings at the Lunar and Planetary Science Conference in Texas. "We saw the first evidence of this in January this year and have since observed 1
The NASA spacecraft, launched in 2016, entered an orbit around Bennu on December 31. It's not the only spacecraft from Earth exploring an asteroid. Hayabusa2, launched by Japan's Space Agency in 2014, began to pave the way of asteroid Ryugu last year. Its mission is also to collect samples to return to our planet for study, and members of their team presented findings at the conference in Texas on Tuesday as well.
Both assignments have found that the objects they study have terrain much more tagged than expected. But while Hayabusa2 already collected its first test from Ryugel's surface last month, the Bennu particles posed an extra challenge to the Osiris-Rex mission. [ Register to get reminders of space and astronomy events in your calendar .]
Varies in size from inches to maybe a few meters in diameter, some of them ejected debris fled Bennu's tough gravity and was launched in the right direction and speed to enter the track, became small moons for at least a short while.
"We really didn't expect to see this activity," Lauretta said.
When the first blast was discovered on January 6, the mission plans made quick calculations to determine if their spacecraft was in danger. "Were we safe in circulation?" Said Rich Burns, project manager for the mission.
With the same tool used to assess the danger of satellites around the earth from orbital debris and meteorites, it concluded that the chances of Osiris-Rex hit by a blow were very low.
The spacecraft may be inaccessible at the moment. But the discovery adds Bennu to a rare category of space stones called active asteroids. Of the 8,000 asteroids discovered, only 12 have been observed to release the material into space. The Osiris-Rex mission team reported these and other findings in seven papers published in the Nature family in magazines on Tuesday.
The Osiris-Rex mission – the name is an abbreviation of Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer – is to study a colise asteroid in the hope of understanding bits in the early solar system and perhaps how the building blocks of life came to earth. (Japan's Hayabusa2 team has a similar mission.)
Bennu, about 1600 meters wide, is covered, almost top to bottom, with boulders. Some are just a few meters wide. The largest, about 250 meters above, radiates like a giant pimple.
The main mission of the spacecraft is to collect samples, and it was designed to aim at a target circle with a diameter of 82 meters. It is brief to place its collecting apparatus, which is similar to a car air filter, on the surface, blowing up a nitrogen exchange and collecting material that is turned upwards.
However, there is no free space at 82 feet on Bennu. Dr. Lauretta and Mr. Burns both expressed confidence that they could steer the spacecraft to a level place. They have time to prepare. Osiris-Rex will not attempt its collection until July next year.
The Hayabusa2 mission surpassed a similar challenge earlier this year at Ryugu, another riotous asteroid.
In outer appearance, Ryugu Bennu – a faceted spin, resembles boulders. Hayabusa2 had been designed to put down Ryugu within an accuracy of 164 feet to collect its sample, but there was no clear loop large enough on the asteroid.
Refined their techniques, the Hayabusa2 navigators were able to move within 9 feet of their target, firing a projectile into their surface to release material for their sample collection tool. In April, Hayabusa2 will shoot a larger bullet in Ryugu to create a crater and let its instruments lie on what is below the surface of the asteroid. Later, the spacecraft can collect another sample from the artificial crater.
While they are similar, measurements show clear differences between the two asteroids. Bennu contains a lot of water-logged minerals while Ryugu – according to articles published Tuesday in the journal Science – seems to hold only wisps of water, as if the material had been heated to hundreds of degrees and dried out.
Ryugu's mineralogical signal could only lie in the surface layer, and during that it is more like Bennu, or the object that the Japanese researchers are studying can be dry all the way. It is one of the things that the excavation of the hill can reveal.
Hayabusa2 will leave Ryugu at the end of a year and come to Earth a year later while Osiris-Rex will stay in Bennu a little longer. It is to resign sometime after March 2021 and release its selection of Bennu in Earth in September 2023.
The documents presented by the Osiris-Rex team also reported additional results on Bennu's form, rotation and surface. Among the results is the possibility that Bennus rotational speed triggers landslides. They can move large amounts of material from the poles down to the equatorial region, causing clumps of rocky debris to build up.
Bennus twirling may also have fed over time, which has contributed to its condensed diamond-like shape. And it doesn't seem to slow down, which can cause its shape to change even more.