Through the analysis of this material collected in 2020 from asteroid Bennu, scientists hope to better understand the formation of the solar system, and how the Earth became habitable.

The landing is scheduled to take place on Sunday around 09:00 local time (15:00 GMT), on a military area normally used to test missiles.

About four hours earlier, more than 100,000 km from Earth, the Osiris-Rex probe must release the capsule containing the sample.

The final descent into the Earth's atmosphere will last 13 minutes: the capsule will enter at a speed of about 44,000 km/h, and the friction caused will raise the temperature to 2,700 ° C.

Image taken by NASA's Osiris-Rex spacecraft, December 2, 2018, showing asteroid Bennu © HO / NASA / Goddard / University of Arizona / AFP / Archives

The fall, observed by army sensors, will be slowed by two successive parachutes, allowing, if all goes well, a soft landing.

The target area is 58 km long and 14 km wide. It's like "throwing a dart through a basketball court, and hitting the center of the target," Rich Burns, mission manager at NASA's Goddard Space Flight Center, said at a press conference in late August.

It could be decided not to release the capsule if it seems, the night before, that the selected area will be missed. The probe would then go around the Sun, before trying its luck again in 2025.

Transported to Texas

"Sample return missions are difficult. A lot can go wrong," said Sandra Freund of partner company Lockheed Martin.

The possibility of a "hard landing", for example if the parachute does not deploy, has been prepared.

Sandra Freund, of partner company Lockheed Martin, during a rehearsal for retrieving NASA asteroid samples for the Osiris-Rex mission, on June 27, 2023 in Littleton, Colorado © Jason CONNOLLY / AFP/Archives

A dress rehearsal took place at the end of August, with a replica capsule dropped from a helicopter.

Once the capsule is on the ground, a team will check its condition before placing it in a net, which will be lifted by a helicopter and carried to a temporary "clean room".

The next day, the sample will be sent aboard a plane to the Johnson Space Center in Houston, Texas.

This is where it will be opened, inside another hermetic room. The priority is not to contaminate the sample with terrestrial material, so as not to distort the analyses. The process will take days.

The laboratory where samples of asteroid Bennu collected by the Osiris-Rex probe will be analyzed, July 24, 2023 in Houston, Texas © Mark Felix / AFP / Archives

NASA is planning a press conference on October 11 to unveil initial results.

Part of the sample will be retained for study by future generations.

250 grams?

Osiris-Rex took off in 2016, and in 2020, the asteroid Bennu surprised scientists when collecting the sample: during the contact of a few seconds with the surface, the arm of the probe had sunk into the ground, revealing a density much lower than expected.

But thanks to this, NASA expects to recover some 250 grams of material -- far more than the original target of 60 grams.

Image from a NASA video showing the robotic arm of the Osiris-Rex spacecraft making contact with asteroid Bennu to collect samples, October 21, 2020 © Handout / NASA TV/AFP/Archives

It is "the largest mass collected beyond the orbit of the Moon," said Melissa Morris, head of the program.

This mission is a first for the United States, but Japan has already conducted two similar ones: in 2010, the Hayabusa probe had brought microscopic grains from the asteroid Itokawa. And Hayabusa-2 reported in 2020 some 5.4 grams of the asteroid Ryugu.

Visually, asteroid Bennu resembles Ryugu, but could turn out to be very different in composition, according to Morris.

Asteroids are interesting because they are composed of the original materials of the solar system, 4.5 billion years ago. While on Earth these have been transformed, the asteroids have remained intact.

Bennu is carbon-rich, and the sample collected is "perhaps representative of the seeds of life that these asteroids delivered at the beginning of our planet, which led to this incredible biosphere," said Dante Lauretta, mission scientist at the University of Arizona.

Bennu, which is 500 meters in diameter, orbits the Sun and approaches Earth every six years.

There is a small risk (1 in 2,700) that it will collide with Earth in 2182, which would have a catastrophic impact. A better understanding of its composition could therefore prove useful. NASA managed last year to deflect the trajectory of an asteroid by hitting it.

© 2023 AFP