On December 31, NASA's Origins, Spectral Interpretation, Resource Identification and Security Regolith Explorer (OSIRIS-REx) met with Bennu's 101955 Asteroid. As part of an asteroid sample return mission, NASA hopes that the material of this near-Earth asteroid (NEA) will reveal information about the history of the solar system, the formation of its planets, and the origin of life on Earth.  Since the space probe has created an orbit around the asteroid, it has experienced some interesting phenomena. This includes the first close-up observations of particle lobes erupting from the surface of an asteroid. Since then, the mission team has been watching for these outbreaks so that eleven "ejection events" have been observed since the spacecraft arrived.
Like all NEAs, Bennu consists of remnants of material from the formation of the solar system. The study of this asteroid is therefore likely to elucidate much about this process and provide insights into the distribution of water and organic molecules in the solar system billions of years ago.
Since the asteroid three months ago Spacecraft the science team has been treated a number of surprises. To begin with, the team found that the surface of the asteroid was much more robust than originally thought, forcing them to change their plan for landing on the asteroid and collecting samples.
In addition, the first ejection event (observed on January 6) was also unexpected, not to mention the subsequent ten outbreaks. As Dante Lauretta, principal investigator of the OSIRIS REx mission at the University of Arizona, said in a recent press release:
"The discovery of feathers is one of the biggest surprises in my scientific career. And the rough terrain contradicted all our predictions. Bennu surprises us already, and our exciting journey there is just beginning. "
The first ejection was discovered after the OSIRIS REx team noticed particles in one of the images of the spacecraft's NavCam 1 imager Bennu circled at a distance of about 1.6 km (1 mi). After assessing the event, the team concluded that the particles posed no risk to the spacecraft and decided to continue monitoring the ejection events.
Although much of the cloud ejected matter was thrown away by Bennu, the team noticed that some of the particles sat as satellites in orbit before returning to the surface of the asteroid. This could mean that a portion of the material (expelled from the interior) can be retrieved as the spacecraft collects samples from the surface.
Lori Glaze, Acting Director of the Planetary Science Division of NASA Headquarters in Washington, summarized these developments:
"The first three months of OSIRIS-REx & # 39; 's thorough investigation by Bennu reminded us What discovery is all about – surprises, quick thinking and flexibility. We study asteroids like Bennu to get to know the origin of the solar system. The pattern of OSIRIS-REx will help us answer some of the biggest questions that ask us where we come from. "
Yet, Bennu's biggest surprise remains his rugged, boulder-strewn surface. Due to observations of the earth, the team expected a relatively smooth surface with a few large boulders. This was based on observations of Bennu's thermal inertia (his ability to conduct and store heat) and radar measurements of his surface.
When the spacecraft arrived, however, the team found that the surface had a significantly higher boulder density than expected. The fact that their first results turned out to be wrong led the team to revise the models used to interpret the asteroid data as they clearly fail to predict the nature of small, rocky asteroid surfaces.
Bennu's rocky surface also means the team's sampling plan – a touch-and-go (TAG) process – needs to be adjusted. Originally it was planned to land at a free place with a diameter of about 50 meters. Due to the boulder density, the team could not find such a large vacancy and instead searched for smaller candidate locations.
This requires much more accuracy from the spacecraft as it descends into the surface, so the mission team is developing an updated approach (Bullseye TAG). Rich Burns – the OSIRIS-REx project manager at NASA's Goddard Space Flight Center – said it had put the mission team through their paces:
"Throughout OSIRIS-REx operations near Bennu our spacecraft and our operations team have been involved It has been shown that we can achieve system performance that exceeds design requirements. Bennu has challenged us to cope with its harsh terrain, and we are confident that OSIRIS-REx will be up to the task. "
Other important findings are the fact that Bennus spin rate is gradually abating. This is the result of the Yarkovsky-O.Keefe-Radzievskii paddock (YORP) effect, where nonuniform heating and cooling results in a reduction in rotational speed. As a result, Bennu's period of rotation slows by about one second per century.
Another interesting find was the presence of magnetite on Bennu's surface, which was picked up by the MapCam colorimeter and the probe's Thermal Emission Spectrometer (OTES). The presence of this mineral reinforces earlier findings suggesting interactions between rock material and liquid water on Bennu's parent company.
These and other findings were presented at the 50th Moon and Planet Conference, which took place March 18-23, Houston, Texas. The findings were also published in a special collection of articles published in the journal Nature
. Further reading: OSIRIS-REx, Nature