OSIRIS-REx (Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer) is the third mission in NASA’s New Frontiers Program which includes medium-class interplanetary missions. Its main objective is to bring soil samples back from an asteroid called Bennu.

This asteroid was discovered in 1999; it has a diameter of about 575 metres and completes an orbit around the Sun every 1.2 years. Its trajectory intersects the orbit of the Earth; according to available data, it may hit it in 2182. Therefore, the mission also aims to better estimate impact hazards.

OSIRIS-REx was launched in September 2016, and arrived at the asteroid in December 2018.

The instruments (cameras, spectrometers, altimeter) begun by measuring Bennu from late 2018 to October 2020, which includes mapping, potential plumes, and presence of natural satellites. They will also measure the Yarkovsky effect, which alters the trajectory of the smallest asteroids—usually less than 20 km. The rotation of the object around its centre causes the return of the solar energy emitted as infrared radiation in a direction that slowly changes its trajectory. This effect is the main source of uncertainty in predicting the trajectories of near-Earth asteroids, and therefore the Earth impact probability. The precise measurement of the Yarkovsky effect on Bennu will further refine the calculation of its orbit and help better assess the risk of a collision.

The instruments will also exploit the images of the surface and will map the asteroid to determine potential regolith sampling sites.

In autumn 2020, the probe will perform a “touch-and-go” of a few seconds to collect a sample (60 g to 2 kg) using a robotic arm. The sample will be stored in a capsule similar to that used by the STARDUST spacecraft. OSIRIS-REx will then study the asteroid for two more years before beginning its return trip in March 2021 for a scheduled arrival in September 2023.

The capsule containing the samples will make a soft landing in the Utah desert. The samples will then be analyzed in laboratory.

CNES has not provided instruments for this mission but it supports the work of several co-investigators involved in the project:

• Patrick Michel, from the LAGRANGE laboratory, is involved in the Carbonaceous Meteorite Working Group (CMWG), the Dynamical Evolution Working Group (DEWG), and the Regolith Development Working Group (RDWG),
• Marco Delbo, from the LAGRANGE laboratory, is involved in the Dynamical Evolution Working Group (DEWG), and in the working group for thermal analysis (to assess the Yarkovsky effect).
• Antonella Barucci, from LESIA-Paris Observatory, is involved in working groups for mineralogy and physical characterization: Spectral Analysis Working Group (SAWG), Thermal Analysis Working Group (TAWG), Imaging Processing Working Group (IPWG), Astronomy and Photometry Working Group (APWG). Several other LESIA’ members are official collaborators of OSIRIS-REx mission: Sonia Fornasier, Frederic Merlin, Marcello Fulchignoni, Alice Praet, Prasanna Deshapriya and Pedro Hasselmann.
• Guy Libourel, from the GeoAzur laboratory, is involved in the Regolith Development Working Group (RDWG) and the Carbonaceous Meteorite Working Group (CMWG). He will analyze the temperature changes of Bennu to assess their impact on the size of regolith grains and thus determine the most suitable sample sites.