2023-09-23 04:00:10
We are living in an extraordinary time for the exploration of the solar system. In the next two decades, samples from asteroids, the Moon, Mars, and perhaps comets will be brought back by dedicated space missions.
Recovery of the capsule containing samples from the asteroid Ryugu in Woomera (Australia) at the end of the Hayabusa2 mission.
JAXA, Author provided
This Sunday, September 24, it is the OSIRIS-REx mission which returns to Earth with samples collected on the asteroid Bennu on October 20, 2020, following two years of observation (Observation is the action of careful monitoring of phenomena , without wanting to…) from a distance, by a delicate “touch-and-go” approach maneuver. The analysis of rocks and dust sampled from an asteroid — which has not evolved for 4.567 billion years — should provide a better understanding of where the material that formed the solar system came from (The solar system is a planetary system composed of a star, the…) and how it evolved in the first millions of years of the universe.
In the coming weeks, scientists will divide up this precious loot and begin analyzing it using different techniques to try to extract information on the nature and origin of primitive matter in the solar system. In particular, the asteroid Bennu sampled by the OSIRIS-REx mission appears to be rich in volatile elements (hydrogen, carbon, nitrogen, noble gases) — a type of matter that may have been at the origin of the atmosphere (Le mot atmosphere can have several meanings 🙂 and terrestrial oceans, cradle of life on Earth.
For their part, engineers will be able to determine how to improve sample collection using this touch method.
Missions have already brought back to Earth samples from the Moon (Apollo) and asteroids (Hayabusa, Hayabusa2). Current and future missions aim to take samples from other planets, such as Mars Sample Return for example, and tell us if life existed there.
The golden age of lunar exploration
In the 1970s, approximately 380 kg of lunar rocks and soils were brought back to Earth thanks to NASA’s Apollo missions and to a lesser extent the Soviet Luna missions. Hundreds of laboratories analyzed the composition of the first samples brought back from another planet. This research made it possible to understand how not only the Moon, but also the other planets were formed and evolved.
The composition of the Sun was clarified by the analysis of 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 sampling lunar soil in 1972.
NASA, Author provided
These lunar missions were above all dictated by strategic issues and this miraculous period for cosmochemistry was unfortunately followed by a lack of interest in this type of mission during the following three decades, the moon no longer having any geostrategic interest.
Meteorites as the 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 were to learn that later). These meteoritic samples of great interest were, however, often degraded by shocks having caused their ejection from their parent bodies and by their interaction (An interaction is an exchange of information, affects or energy between two agents within… ) with the terrestrial environment.
So, in the 2000s, sample return missions resurfaced under the leadership of American geochemists. The NASA Genesis mission sampled the solar material ejected by our star, the analysis of which made it possible to resolve two major cosmochemistry problems: the isotopic compositions of oxygen and nitrogen whose significant and not understood variations were used as indicators of filiation between different planetary bodies.
The NASA Stardust mission sampled some cometary grains as the spacecraft passed through the tail of comet Wild2. These grains, strongly degraded during high-speed sampling, nevertheless made it possible to show the mixing of matter in the disk surrounding 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 millions of years.
Comet grains recovered by NASA’s Stardust mission. The particles were implanted in airgel, a low-density material that cushioned their capture. The particles with a speed of 6 km/s literally exploded at the entrance (cavities at the top) and terminal grains traveled approximately 1 cm in the aerogel. This is the first return to Earth of a cometary sample.
NASA, Author provided
Heading for the asteroids: The Hayabusa and Hayabusa2 missions
In 2010, the Hayabusa mission (“hawk” in Japanese) brought back a few milligrams of grains sampled from the asteroid Itokawa. Several technical problems that almost derailed this return 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.
Hayabusa2, which returned to Earth on December 5, 2020 in Woomera in Australia, aimed to sample an asteroid of another type, called Ryugu, which was supposed to be rich in organic matter (Organic matter (OM) is the carbonaceous matter produced generally by…) and in minerals having interacted with liquid water.
Hayabusa2 took off in 2014 and reached its target in 2018. The robot sampled grains and dust in two locations. The second sampling was particularly acrobatic since it consisted of first sending an explosive charge, the spacecraft having dropped it having taken refuge behind the asteroid, then taking fresh material from the center of the crater formed. The sampling was sent to the JAXA center in Tokyo, where scientists were pleasantly surprised to discover 5.4 grams of grains and black dust, 50 times more than the expected nominal quantity.
Modern analytical techniques have allowed dozens of laboratories to analyze these Ryugu grains virtually at the atomic level, while retaining half for future generations — a strategy similar to that used for lunar samples, part of which had also been preserved for later analyses, with more refined techniques, which made it possible to increase by several orders of magnitude the quality of the analyzes of lunar samples carried out in the 1970s.
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 of the asteroid Ryugu.
JAXA, Author provided
What’s new for OSIRIS-REx For its part, the OSIRIS-REx mission will bring back around 200 grams of material from the asteroid Bennu, making it possible to study its diversity before its homogenization, during the growth processes of the planets. The abundance of sampling will also make it possible to carry out analyzes requiring larger quantities than those brought back by Hayabusa2, notably concerning primordial organic matter, chiralitythe possible presence of amino acids.
Two teams, Japanese and American, are actively collaborating on these two missions. The Osiris Rex mission, costing 650 million Euros, 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 might not close, 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 primitive matter in the solar system and that of the atmosphere and oceans.
Sampling of the asteroid Bennu by NASA’s Osiris Rex probe. In the absence of gravity, the probe might not remain on the surface, and sampling consisted of a touch and go during which a jet of nitrogen pushed the grains into the receptacle at the end of the arm.
Future extraterrestrial sample return missions
Unlike other international space agencies, the European Space Agency (ESA) has not developed a specific return mission. sample, despite the dynamism of the European cosmochemical community, preferring to concentrate on sending space telescopes to observe exoplanets, and favoring in situ observation missions, such as the Rosetta mission which successfully analyzed the composition of the comet 67P/Churyumov-Gerasimenko. However, ESA has partnered with NASA to bring back samples from Mars in 2031-2033, for a total cost that will exceed 7 billion Euros. This is a complex set of successive missions, the failure of one of which will compromise the return of Martian matter. This project is of course part of the perspective of sending humans to Mars: before bringing people back, we must first characterize the Martian environment as best as possible, and, prosaically, be able to bring back something of the red planet! A rover is on its way to sample fossil lake deposits, with among other things the hope of finding traces of past or even current life. This search for biological activity also has a downside for geochemists: the samples must be treated in a P4 type biological room, until they are declared biologically inert by sterilization. Indeed, these confinement constraints will not allow the analytical finesse planned given the complexity and the size of the necessary equipment.
The party won’t stop there: JAXA’s MMX mission, which will take off in 2024, will sample one of the two moons of Mars with a return to terrestrial laboratories in 2029.
The Chinese space agency CNSA also has big ambitions in this area, planning to sample the Moon – something it has already started to do with the Chang’e-5 mission which brought back the youngest basalts from our satellite on December 16, 2020. But China also wants to bring samples from the asteroid Kamo’oalewa back to Earth around 2032 (Zheng He mission) and from Mars by 2040 or before.
Several American projects aim to analyze cometary material brought back to Earth, although no mission has been selected for the moment. In addition to their scientific interest, this type of mission also has the consequence of increasing technological knowledge of the space domain, and of boosting analytical technology, of which Europe is one of the leaders.
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