Asteroid Bennu - interim summary before Osiris Rex collects a sample from it and returns it to DHA

In July 2020, the Osiris Rex spacecraft will collect a sample from the asteroid Benu, which it has orbited since the end of 2018. An opportunity to see what we have learned about the carbonaceous asteroid, which also has a risk of colliding with Earth in over a century

In July 2020, the Osiris Rex spacecraft will extend a robotic arm that will collect from the surface of the asteroid Bennu a sample weighing between 60 grams and 2 kilograms, and will bring it to Earth in 2023. This is an opportunity for an interim summary of the science collected by the spacecraft in a little more than a year that it orbits the asteroid.

His son was discovered in 1999. It turned out that this is a very tiny body and that its diameter is 575 meters. The nickname given to him 36RQ 1999 and the name Bennu. This asteroid was chosen as a target to bring soil samples from. The spacecraft designed for this purpose was named REx-OSIRIS. The launch year is 2016. The accepted estimate is that it was formed in the early days of the solar system, so it will be possible to test the early days of the solar system through the soil test.

Beno was also chosen because it is a C-type asteroid, the richest in carbon, a key element in organic compounds essential to sustaining life. Organic molecules, such as amino acid, have previously been found in meteorites and comet samples, suggesting that certain substances necessary for life can be formed in outer space. The Bennu asteroid is considered to have a relatively high risk of colliding with Earth. The orbit of the Bennu asteroid brings it to a distance of 0.002 astronomical units from the Earth every 6 years.

The plan (which has been carried out successfully so far) was that in 2019 the spacecraft would enter orbit around it, staying near it for a year. During this period the asteroid will be photographed, measured and studied. At the end of this year in 2020, the spacecraft will collect 60 grams of soil from it, take off from it, return to Earth and land in September 2023. The asteroid has been mapped and the surface has been given names. The place chosen for sampling was named Nightingale. As soon as the approval for soil sampling is given, the spacecraft will leave its orbit and slowly descend towards the surface. As soon as it is selected for this purpose, compressed gas will be released from the facility adjacent to it and upon hitting the ground, it will spray upward tiny rock particles that will be collected by the spacecraft into a suitable container. This action will last a few seconds and then take off and return to Earth (1). So far the spacecraft is working as planned.

The gravity of this body is almost zero - 1/100,000 of that of the Earth and it rotates around itself once every 4.3 hours (2). Because of its tiny dimensions, it is likely that it was torn from a large body hundreds and thousands of kilometers away for whatever reason. The size of the craters on its surface is also corresponding, tens of meters in diameter, they are shallow and their ground is flat. It is likely that this is also the case with thousands of other asteroids of this size. They are actually flying mountains. If we compare them to asteroids that are tens of kilometers in size, the latter have craters on the order of kilometers in size. Examples of this can be found in the tiny moons surrounding the gaseous planets. It is possible that in the future in the asteroid belt and also in those orbiting the moons of the gaseous planets, moons of the size of Bennu will be found orbiting them. It will be possible to do comparative studies. If they want to land spaceships on them, the appropriate order of magnitude will be nano spaceships.

Based on telescopic observations, it was estimated that Bennu is one of the dark bodies in the solar system and that it has many smooth areas including 2.5 cm gravel and pebbles over 50 meters in size. In this place they found a small number of areas with rocks between 20-5 meters in size that could cause damage to the spacecraft when it descends to the ground for sampling. 200 large rock blocks (boulders) measuring more than 10 meters and those measuring more than 1 meter were identified. The largest rock was 58 meters high. All of these required a redesign of the landing. Bennu reflects only 4% of sunlight.

The surface of the asteroid is older than thought, although relatively recent activity has been observed. They also noticed the ridges moving from pole to pole and indicating the flow of material on the ground. This material fills the large craters. A lack of small impact craters indicates a dynamic terrain. The asteroid has many internal spaces up to 60% porosity. It gives the impression that the internal stiffness is strong enough to create friction inside the asteroid, which allows cracking of the surface of the ground.

Spectroscopic and visible light tests confirm that Bennu is a carbonate chondritic asteroid. It was also found that hydric minerals are common on the surface of the soil and there is evidence of the presence of molecules containing hydrogen and oxygen bound between them. It is estimated that these hydroxyl groups are found in the clays on the surface. The asteroid itself is too small to have liquid water. The only possibility that the source of the water is in the source body from which the asteroid came (2).
An interesting observed phenomenon is the movement of gravel particles from the surface of the asteroid into space. This phenomenon was observed 11 times. Some of these particles returned to the ground, some entered orbit around the asteroid and some flew into space. There is no explanation for the phenomenon (3).
Sources
1. Stephen C. – NASA selects site for Osiris RFx to collect asteroid samples 12.12.2019
2. 'Osiris – Rex” spacecraft studies asteroid Bennu up close"20.3.2019

3. Stephen Clark -“Osiris-Rex spacecraft finds particles flying off asteroid Bennu"19.3.2019