Bennu (101955) is a small asteroid orbiting the Sun in an orbit close to the Earth’s orbit (the orbit period is 1 year 71 days 8 hours). The object is extremely interesting for researchers, among others because on its way around our star in the second half of the XXII century it will fly dangerously close to our planet eight times.
NASA has long planned to explore Bennu more closely, and in September 2016, the Origins probe, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) towards the asteroid. The ship arrived in Bennu in early December 2018, and after a few days discovered the presence of hydroxyl groups in the asteroid’s minerals, meaning there was water on the larger object that Bennu was once part of. On the last day of 2018, OSIRIS-REx entered orbit around the asteroid, becoming the first ever artificial satellite of such a small space object.
Bennu throwing rocks into space fot. NASA / Goddard / University of Arizona / Lockheed Martin
NASA’s goal is to surface Bennu
Since then the OSIRIS-REx probe flooded us with new, unusual information about Bennu, and also delivered a great deal photographs showing the rocky surface of the asteroid (taking such pictures from Earth would be impossible). Thanks to them, it was possible to make a more detailed map of Bennu than the most accurate maps of our Moon.
All these studies made it possible to select the best place on Bennu for OSIRIS-REx in December 2019. After another month wash NASA has set the date of “landing” on October 20, 2020 – that is, next Tuesday.
Planned attachment site for the OSIRIS-REx probe:
‘Nightingale’ – the probe landing site fot. NASA / Goddard / University of Arizona
A very unusual landing
It is worth adding, however, that “landing” is a word that does not accurately describe the operation that NASA has to perform. The OSIRIS-REx probe has been equipped with a robotic arm that is designed to attach the probe to the asteroid. Scientists will lower the height of the OSIRIS-REx so much that the ship will “catch” the asteroid – although it will hover just above the stones covering the asteroid’s surface.
All because Bennu is an extremely small facility. It has a diameter of about 560 meters, so it is smaller than some asteroid moons (almost three times as large it is e.g. Dactyl – the moon of the asteroid Ida). The small mass of the object makes the classic landing on the surface of Bennu impossible – the gravitational field of the asteroid is so small that it is too risky, if even feasible, to place the probe in a certain place on the surface.
Asteroid Bennu fot. NASA / Goddard / University of Arizona
When the two objects come into contact, OSIRIS-REx will direct a stream of compressed nitrogen at the surface of Bennu, lifting stones from it, which will then be captured by the probe’s boom. The entire operation will take just a few seconds, after which the OSIRIS-REx will fire the engines and drive away to a safe distance from Bennu. Importantly, all activities will be performed by the probe independently, according to a predetermined scenario. This, of course, is due to the enormous distance (334 million km) that separates the Earth and Bennu. The delay with which the signal from OSIRIS-REx reaches us is as much as 18.5 minutes, which makes remote control of the device from Earth impossible.
Rocks from Bennu will fly to Earth
OSIRIS-REx is one of the most interesting and unique missions carried out in recent years by NASA. All because the probe sent to Bennu is designed to return to Earth providing scientists with the collected samples. The space agency assumes that it will be able to collect from about 60 g to about 2 kg of samples from the surface of Bennu. It will be extremely valuable research material, thanks to which scientists will be able to learn much more than before about the nature of asteroids orbiting the Sun.
Of course, we will have to wait a little longer for the return of OSIRIS-REx. After sampling, the probe will return to orbit around the asteroid, where it will wait for another window to open, allowing it to return to March 2021. If everything goes according to plan – the ship should land on our planet on September 24, 2023 – after seven years spent in space.
Much earlier, however, we will be able to trace the sampling operation from the surface of Bennu. NASA on the night of October 20 to 21 (Polish time) will carry out broadcast during which he will present and discuss the course of the mission live.