A NASA asteroid-sampling probe has entered the homestretch of its deep-space journey.
The OSIRIS-REx spacecraft began its final approach toward the big near-Earth asteroid Bennu on Friday (Aug. 17), NASA officials said. The milestone also marks the official start of OSIRIS-REx’s “asteroid operations” mission phase, they added.
OSIRIS-Rex stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer.
OSIRIS-REx is the third mission in NASA’s New Frontiers program, which previously sent the New Horizons spacecraft zooming by Pluto and the Juno spacecraft into orbit around Jupiter.
OSIRIS-REx will spend two years traveling towards Bennu, arriving at the asteroid in August 2018. The probe will orbit the asteroid for 3 years, conducting several scientific experiments, before returning to Earth, with the sample capsule expected to land in Utah, the USA in September 2023.
During its three year orbit of Bennu, OSIRIS-REx will be conducting a range of scientific experiments in order to better understand the asteroid.
As part of this, the asteroid will be mapped using instruments on the probe, in order to select a suitable site for samples to be collected from.
The aim of the mission is to collect a sample of regolith- the loose, soil-like material which covers the surface of the asteroid.
In July 2020, the probe will move to within a few meters of Bennu, extending its robotic arm to touch the asteroid’s surface. The arm will make contact with the surface for just 5 seconds, during which a blast of nitrogen gas will be used to stir up the regolith, allowing it to be sucked into the sample collector.
OSIRIS-REx has enough nitrogen on board for 3 sample collection attempts, and NASA is hoping to collect between 60 and 2000g of regolith material to bring back to Earth.
Bennu was selected for the OSIRIS-REx mission from over 500,000 known asteroids, due to it fitting a number of key criteria. These include:
Proximity to Earth: In order for OSIRIS-REx to reach its destination in a reasonable timeframe, NASA needed to find an asteroid which had a similar orbit to Earth. Around 7000 asteroids are ‘Near-Earth Objects’ (NEOs), meaning they travel within around ~30million miles of the Earth. Out of these, just under 200 have orbits similar to Earth, with Bennu being one of these.
Size: Small asteroids, those less than 200m in diameter, typically spin much faster than larger asteroids, meaning the regolith material can be ejected into space. Bennu is around 500m in diameter, so rotates slowly enough to ensure that the regolith stays on its surface.
Composition: Bennu is a primitive asteroid, meaning it hasn’t significantly changed since the beginning of the Solar System (over 4 billion years ago). It is also very carbon-rich, meaning it may contain organic molecules, which could have been precursors to life on Earth.
Additionally, Bennu is of interest as it is a Potentially Hazardous Asteroid (PHA). Every 6 years, Bennu’s orbit brings it within 200,000 miles of the Earth, which means it has a high probability of impacting Earth in the late 22nd Century.