It might be 60 grams – which is the target – or it might be as much as a kilogram. We don’t yet know how much material was blown into the cannister – and we won’t know until it arrives back on Earth in September 2023.
Collection over, and the spacecraft backed away – hence the relief at mission control at the "back away, burn complete" message, showing that OSIRIS-Rex was moving away from the surface. The slow approach to the surface took several nail-biting hours, while the collection operation took a matter of seconds. It did this by blowing a jet of nitrogen gas onto the surface, which was sufficiently powerful to throw material into the collection cannister. This is why NASA used the touch-and-go approach – the spacecraft approached the asteroid very slowly, hovering only a meter or so from its surface, while an arm was extended to touch the surface to collect a sample. A lander would bounce off, back into space. It was always going to be tricky to collect material from the surface – any attempt to land would be unlikely to succeed, because the low gravitational pull of Bennu would not grab onto a lander and hold it in place. It will also tell us the physical properties of something that might hit the Earth, potentially helping us stop it. Studying these materials will help us understand the primitive dust from which the solar system grew, and the range of organic compounds present. While this ice will not be collected by OSIRIS_Rex, the effects of water should be seen in the material it’s gathered. There is no running water there now – but there might be small pockets of ice below the surface. Clay and carbonates require water – lots of it – so these minerals must have formed when Bennu was part of a larger asteroid. It is also believed to be rich in the type of organic compounds that might have seeded the Earth to enable life to arise.Īnother surprising find that came from the mapping campaign was that Bennu was not only rich in clay minerals, but that veins of carbonate were present. Secrets of the solar systemīennu is a Near Earth Asteroid – it has a one-in-2700 chance of colliding with the Earth in about 170 years’ time. This made selecting a site for sample collection more difficult. One of the consequences of the activity – explained by changes in temperature fracturing larger boulders (opens in new tab) and breaking up the rocks - is that the surface of Bennu is completely covered in rubble, much more than had been expected. (Image credit: NASA/Goddard/University of Arizona) Image of Bennu taken by OSIRIS-REx in 2018.
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