On September 24, an asteroid sample taken from space will land on Earth. The Canadian Space Agency (CSA) team is excited, because thanks to its contribution to this mission, it will be able to recover a portion of this celestial body. And its study should help to better understand the formation of the solar system and the emergence of life on Earth.
Launched on September 8, 2016, the space probe OSIRIS-REx arrived near the asteroid Bennu on December 3, 2018. It then remained in orbit around this star for two years, during which it collected data which allowed it to select a suitable sampling site.
A sample of Bennu was finally taken on October 20, 2020. A few months later, the probe began the return journey to Earth. And it is on September 24 that it must release the capsule containing the asteroid sample. The latter will pass through the Earth’s atmosphere before landing in the Utah desert. The probe OSIRIS-RExfor its part, will leave for other skies.
What is the point of such a mission when asteroids – or at least fragments – are already present on the ground of our planet? “These fragments that fell to Earth were exposed to extreme temperatures as they passed through the atmosphere and they may have suffered contamination during the thousands of years they spent on the Earth’s surface, where the importance of going into space to look for an intact sample which has not been altered either by the earth’s atmosphere or by terrestrial compounds”, argues Caroline-Emmanuelle Morisset, scientist in the planetary sciences program at the ASC.
“We think that an asteroid like Bennu constitutes a piece of the beginning of the formation of the solar system, it perhaps even contains fragments which would be older than the solar system. Collecting a sample from Bennu will allow us to open a window on the beginning of the formation of the solar system, to understand its formation and its origin,” she continues.
Remaining almost intact since the formation of the solar system 4.6 billion years ago, Bennu represents an important witness to this distant era. It should provide clues to how planets formed.
Asteroids like Bennu formed early in the formation of the solar system, when energy began to decrease and clouds of matter condensed and solidified, the scientist explains. But unlike planets, asteroids have not differentiated and are much smaller in size.
Clues to the emergence of life?
In addition, Bennu “probably contains organic compounds and water, the ingredients necessary for life,” notes Mme Morisset. “Studying these ingredients contained in an asteroid can give us clues about how life appeared on Earth and the role of asteroids in this process,” she says. Because some put forward the hypothesis that the chemical elements essential for the emergence of life on Earth come from meteorites falling on it.
Those responsible for the mission OSIRIS-REx chose the asteroid Bennu as their target for various reasons. First, because it passes close to our planet every six years: its orbit even crosses that of the Earth, which makes the movement of a probe easier and shorter. Then, because the selected asteroid had to have a diameter of more than 200 meters, because the smallest asteroids rotate too quickly. “It is more difficult to approach an asteroid and take a sample from its surface if its rotation speed is very high,” underlines Mme Morisset.
Five asteroids met these criteria. Bennu was favored because it appears to be particularly rich in carbon — and for this reason it could provide clues to the emergence of the first organic molecules. It is also 500 meters in diameter and rotates in 4.3 hours, which made it possible to take a sample without any problem.
Before proceeding with this delicate maneuver, the probe OSIRIS-REx mapped Bennu’s surface in detail using the Canadian OLA instrument (OSIRIS-REx Laser Altimeter), which, like radar, emits a laser beam towards the asteroid and captures what is reflected by the surface. The time elapsed between the emission and reception of these pulses makes it possible to determine the distance between the probe and the surface, and thereby to draw up “with exceptional resolution” a three-dimensional topographic map of the asteroid.
“The surface was expected to be smoother, but it was littered with debris and fragments, which made selecting a site to sample more difficult. But one of the biggest surprises we had was that this debris was quite loose. When the robotic arm approached to take a sample, the surface was expected to be hard. However, the sampler was easily submerged up to 50 cm deep. We even had to turn on the probe to move back and stop the arm,” says the researcher.
As the CSA provided the OLA, it will receive 4% of the sample collected. “We will keep it under pure nitrogen, which is an inert gas which will prevent reactions with the atmosphere. We want it to be preserved as it was found in space,” explains M.me Morisset.
This piece of asteroid will then be made available to the scientific community, both Canadian and international, for study.