This Sunday, September 24, is the mission OSIRIS-REx which returns to Earth with samples collected from the asteroid Bennu on October 20, 2020, after two years of remote observation, through a delicate “touch-and-go” approach maneuver. Analysis of rocks and dust taken from an asteroid (which has not evolved for 4.567 million years) should provide a better understanding of where the material that formed the solar system came from and how it evolved in the universe’s first few million years.
In the coming weeks, scientists will divide up this precious loot and begin to analyze it using different techniques to try to extract information about the nature and origin of the primitive matter in the solar system. In particular, the asteroid Bennu sampled by the mission. OSIRIS-REx It appears to be rich in volatile elements (hydrogen, carbon, nitrogen, noble gases), a type of matter that may have been at the origin of Earth’s atmosphere and oceans, the cradle of life on Earth.
For their part, engineers will be able to determine how to improve sample collection using this tactile method.
Missions have already brought samples from the Moon to Earth (Apollo) and asteroids (Hayabusa, Hayabusa2). Current and future missions aim to take samples from other planets, like Mars Sample Return, for example, and tell us if life existed there.
The golden age of lunar exploration
In the 1970s, missions brought about 380 kg of lunar rocks and soil to Earth Apollo of NASA and to a lesser extent to the Soviet missions to the Moon. Hundreds of laboratories analyzed the composition of the first samples brought from another planet. This research allowed us to understand how not only the Moon, but also the other planets, formed and evolved.
The composition of the Sun was elucidated by analyzing solar ions implanted in lunar soils and the nature and flow of external matter on planetary surfaces was quantified. These investigations required the development of new analytical methods, which have improved over time, and whose limit is now the atomic scale.
Harrison Schmidt, astronaut and geologist on the Apollo 17 mission that sampled lunar soil in 1972. NASA, Author provided
These lunar missions were dictated above all by strategic issues and, unfortunately, this miraculous period for cosmochemistry was followed by a lack of interest in this type of missions for the next three decades, since the Moon no longer had any geostrategic interest.
Meteorites as only spies.
Historically, the only extraterrestrial samples available were meteorites. These come from small celestial bodies: asteroids (as well as from the surface of the Moon and Mars, but we learned that later). However, these meteorite samples of great interest were often degraded by shocks that caused them to be ejected from their parent bodies and by their interaction with the terrestrial environment.
Thus, in the 2000s, sample return missions reemerged under the leadership of American geochemists. NASA’s mission Genesis They took samples of the solar material ejected by our star, the analysis of which made it possible to solve two major cosmochemical problems: the isotopic compositions of oxygen and nitrogen, whose significant and not understood variations were used as indicators of affiliation between different planetary bodies.
NASA’s mission star dust allowed taking samples of some comet grains during the spacecraft’s passage in the comet’s tail savage2. These grains, strongly degraded during high-speed sampling, nevertheless made it possible to show the mixture of matter in the disk that surrounds our star, from its most central regions to the outer solar system, the reservoir of comets. These results provided a better understanding of how stellar systems (central star and planetary disk) form and evolve during the first few million years.
Comet grains recovered by NASA’s Stardust mission. The particles were implanted in airgel, a low-density material that cushioned their capture. Particles with a speed of 6 km/s literally exploded at the entrance (cavities at the top) and the terminal grains traveled approximately 1 cm into the airgel. This is the first return to Earth of a comet sample. NASA, author provided
Heading to asteroids: The Hayabusa and Hayabusa2 missions
The mission Hayabusa (“hawk” in Japanese) brought back in 2010 a few milligrams of grains taken from samples of the Itokawa asteroid. Several technical problems that almost derailed this comeback were overcome thanks to the ingenuity of Japanese engineers and technological miracles. This mission established a link between this asteroid and a well-defined class of meteorites.
Hayabusa2which returned to Earth on December 5, 2020 in Woomera (Australia), had the objective of taking samples from an asteroid of another type, called Ryugu, which was supposed to be rich in organic matter and minerals having interacted with liquid water.
Hayabusa2 It took off in 2014 and reached its goal in 2018. The robot took samples of grains and dust at two locations. The second sampling was especially acrobatic, since it consisted of first sending an explosive charge, which the ship dropped sheltered behind the asteroid, and then collecting fresh material from the center of the crater formed. The sample was sent to the JAXA center in Tokyo, where scientists were pleasantly surprised to discover 5.4 grams of grains and black powder, 50 times more than the expected nominal amount.
Modern analytical techniques have allowed dozens of laboratories to analyze these Ryugu grains virtually at the atomic level, preserving half for future generations, a strategy similar to that used for lunar samples, part of which had also been preserved for later analysis. , with more refined methods. techniques, which allowed the quality of the analyzes of lunar samples carried out in the 1970s to be increased by several orders of magnitude.
The analyzes showed that the Ryugu samples are exceptionally rich in volatile elements. They allow us to explore possible connections between this primitive matter and the volatile elements of the planets.
Grains from the asteroid Ryugu. JAXA, Author provided
What’s new for OSIRIS-REx
For its part, the mission OSIRIS-REx It will bring around 200 grams of material from the asteroid Bennu, which will make it possible to study its diversity before its homogenization, during the growth processes of the planets. The abundance of sampling will also allow analyzes that require larger quantities than those provided by Hayabusa2in particular on primordial organic matter, chirality and the possible presence of amino acids.
Two teams, Japanese and American, actively collaborate in these two missions. The Osiris Rex mission, which cost €650 million, was launched in 2016 and achieved its goal two years later. The spacecraft patiently mapped the asteroid for two years.
Sampling took place on October 20, 2020. The process was so efficient that the sampler lid could not be closed, forcing the team to quickly store the samples in the return capsule.
The return to Earth scheduled for September 24, 2023 will allow numerous international teams, including ours, to explore in detail the origin of the primitive matter of the solar system and that of the atmosphere and oceans.
bennu. Sampling of the asteroid Bennu by NASA’s Osiris Rex probe. In the absence of gravity, the probe could not remain on the surface, and sampling consisted of a touch-and-go during which a jet of nitrogen pushed the grains toward the receptacle at the end of the arm, CC BY
Future extraterrestrial sample return missions
Unlike other international space agencies, the European Space Agency (ESA) has not developed a specific sample return mission, despite the dynamism of the European cosmochemistry community, which prefers to concentrate on sending space telescopes to observe exoplanets and favors in situ observation missions, such as the mission rosette who successfully analyzed the composition of comet 67P/Churyumov-Gerasimenko.
However, ESA has partnered with NASA to bring samples back from Mars in 2031-2033, for a total cost that will exceed €7 billion. It is a complex set of successive missions, the failure of one of which will compromise the return of Martian matter. This project, of course, is part of the perspective of sending humans to Mars: before bringing them back, we must first characterize the Martian environment as best as possible and, prosaically, be able to bring something back from the red planet! A rover is on its way to sample fossil deposits in lakes, hoping, among other things, to find traces of past or even current life. This search for biological activity also has a drawback for geochemists: the samples must be treated in a P4 type biological room, until they are declared biologically inert through sterilization. In fact, these confinement limitations will not allow for the anticipated analytical precision given the complexity and size of the equipment required.
The party won’t stop there: JAXA’s MMX mission, which will take off in 2024, will take samples from one of the two moons of Mars and return to Earth laboratories in 2029.
The Chinese space agency CNSA also has big ambitions in this area and plans to take samples from the Moon, something it has already started doing with the mission. Chang’e-5 which brought the youngest basalts from our satellite on December 16, 2020. But China also wants to bring samples from the Kamo’oalewa asteroid to Earth around 2032 (mission Zheng He) and Mars by 2040 or sooner.
Several American projects aim to analyze cometary material brought to Earth, although no mission has been selected at the moment. In addition to their scientific interest, this type of mission also has the consequence of increasing technological knowledge in the space field and promoting analytical technology, of which Europe is one of the leaders.
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