This fall, two missions of space exploration devoted to the study of asteroids will enter into the heart of their subject : a japanese named Hayabusa2, and the other american named OSIRIS-REx. As the French and Germans, as partners of the japanese space agency Jaxa, in the absence of european mission, they are about to try to ask their lander MASCOT to the surface of one of these small bodies named Ryugu. But why is there so much interest for these big rocks in the solar system ?

first, because, like comets, like 67P/Tchourioumov-Guérassimenko visited by the Rosetta probe, these objects are considered as primitives are able to shed light on the formation of our solar system. “Precisely on its origin and its evolution “, explains Antonella Barucci, an astronomer at the Observatory of Paris-Meudon and a member of both missions. “The difference is that the asteroids formed in the inner solar system as comets, they are born much further away from our star. Thus, even if there has been a few exchanges of materials by the following and that we tend to make less and less distinction, this small body we tell the same story from a point of view that is significantly different “, she adds. “Asteroids tell us more about the formation of Earth and earth-like planets as comets. What is particularly interesting, ” says, for his part, Patrick Michel of the Observatoire de la Côte d’azur, also a member of two missions.

In reality, asteroids evolving mainly between the orbits of Mars and Jupiter are even what scientists call planetesimals. That is to say, of the kinds of bricks from which the planets formed. They have just not managed to assemble to form because of the gravitational influence of the two planets already formed.

A history of water and carbon

The second point of interest, and not the least, is that the asteroids can also teach us something about the origin of life. “In fact, one of the proposed scenarios for the appearance of alive is that the ingredients that have allowed it to emerge, namely water and organic matter, have been brought to Earth by asteroids during a great bombardment,” says the astrophysicist. “Before, we thought that the water had instead been brought by comets, but, when we investigated a marker-key to determine the origin of the latter, namely, the report deutérieum/hydrogen, we have found that the comet was almost always different from that of the Earth. The water present on the surface of our planet, therefore, could not have come from them, ” says Antonella Barucci. “On the other hand, the meteorites of type chondrites carbonaceous – that are found on Earth and that are the vast majority of the asteroids have exactly the same ratio of deuterium to hydrogen that water from our oceans and our rivers. “This means that the precious liquid may have been provided by them. And that’s not all ! Because the chondrites of which there is question is derived primarily from asteroids so-called type-C, such as carbon. However, that said carbon said carbon. And who said carbon approximates the chemistry of life. In fact, all life as we know it is based on the atom whose ability to bind to other elements, in multiple ways, provides the most remarkable set of chemical construction of the whole Universe. From there to imagine that these asteroids have also been able to make on Earth all or part of the building blocks of life, there is therefore only one step.

sample Return

“This is the reason why we need to bring back samples of these asteroids to analyze on Earth [much more finely than would the more talented of the robots posed to their area, editor’s NOTE] and it is precisely the main objective of the missions, Hayabusa2, and OSIRIS REx, which are both parties to the encounter of asteroids potentially rich in carbon : Ryugu and Bennu,” says Patrick Michel. The mission Hayabusa2 must make three samples and plans to bring between 0.1 and 1 gram of material in total. “Which can already allow for multiple analyses and bring us really a lot of information,” swear Antonella Barucci. As for Nasa, even more ambitious, it relies on the collection of 60 grams to 2 kilograms in a single point.

But is there a way to talk about organic matter as we speak the water ? “Yes, considers the scientific. Because there are two forms mirrors of amino acids, as you have a left hand and a right hand. This property which arises simply from the shape of the molecule [that is related to the plasticity of the carbon atom mentioned above, editor’s NOTE] is called the chirality. A priori, the two forms exist in equal amounts in nature except that, without knowing why, the proteins of living beings, they, contain a majority of “left hands”. “By studying the composition of asteroids Ryugu and Bennu, the researchers hope to be able to tell if the organic material of these asteroids has the same features as the building blocks of life.

beyond the science

But the scientists are not the only ones to pay close attention to the physical properties and the chemical composition of these small bodies. “Other communities need the same information for different reasons,” notes Patrick Michel. In fact, in an objective of planetary defense, in case of impact, announced with an asteroid, the specialists need to know more about the enemy to develop their response. More than an attempt to destroy the asteroid by taking the risk of having to face multiple impacts of the spin-off of the biggest songs from his dislocation, the first proposed solution is to divert it. “Except that it should obviously not exercise the same force to deflect a metal bar and a sponge… “, says the French researcher who argues for a test of the deflection of the asteroid as well as a comprehensive inventory of neas (those whose orbit intersects that of the Earth) of at least 100 meters in diameter. “Because, if the fall of an asteroid is the natural disaster, the less likely it is also the only that one can predict and avoid… provided you give the means. “

Thus, by studying the morphology of craters present on the surface of Ryugu and Bennu, photographed by the probe, the professionals of global security will they have the opportunity to better understand how these bodies react to the impacts. A given which is not without interest to a last category of actors : companies or even whole countries, such as Luxembourg – which has made it a national policy – or the United States, hope to be able to, one day, use the resources present in asteroids. Whether it’s precious metals, building materials or components for the manufacture of water, fuel or batteries for the conquest of space, the researchers must identify these resources and learn more about the asteroids themselves in order to be able to determine how to exploit them.


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