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[EN VIDÉO] The 42 largest main-belt asteroids observed by the VLT The VLT instrument Sphere has observed the largest main-belt asteroids between Mars and Jupiter.
The Apollo missions and the interplanetary probes launched in the 1970s made it possible to largely confirm a few years ago a scenario developed in the past few decades of the birth of planets and comets in a gas- and dust-rich protoplanetary disk surrounding a young Sun . about 4.56 billion years old.
This scenario allows rocky planets such as Earth, Mercury or Mars to form and grow through accretion, with a bombardment of asteroids and comets, traces of which can still be found in the form of lunar craters. The water in Earth’s oceans must have come from this bombardment, but debate over the precise nature of the small celestial bodies responsible for this contribution has continued for decades. In other words, does water come mostly from comets or asteroids?
Futura has devoted many articles to this debate and today a new article was added to it via an article in Nature Astronomy. She reports certain results of the analyzes of material samples returned to Earth by the Japanese probe Hayabusa-2 in late 2020. These samples come from the asteroid Ryugu (“dragon palace” in Japanese), a member of the Apollo family of asteroids, type C due to a composition close to carbonaceous chondrites found on Earth, and located in more than 300 million kilometers away from our planet.
Examination of its samples, less than 900 meters in diameter, confirmed that it contained original material dating from the formation of the solar system, which had been little modified despite traces of heating and circulation of liquid water, but whose temperature did not exceed 30 °C was allowed c
Hydrogen isotopes as cosmogonic tracers
The cosmochemists studying the samples from Ryugu say today that the analyzes of the isotopic abundances of hydrogen and nitrogen again point to the relationship between the water of the asteroids and that of the oceans on Earth.
To understand what this is all about, just remember that there are of course two types of water, one, ordinary, consists of hydrogen H atoms with a single proton as the nucleus; the other, called heavy, consists of deuterium D atoms, i.e. a nucleus with a proton and a neutron.
A fraction of the water on Earth is made up of molecules that contain deuterium instead of a hydrogen atom. We can therefore define a D/H isotope ratio, which in cosmochemistry is an indicator of the origin of seawater.
Therefore, by comparing this ratio with that found in meteorites and comets, it is possible to determine the parents of the waters of the oceans. For years the thesis of an origin of this water by volcanic outgassing of the young earth has been abandoned and the pendulum has not stopped swinging alternately either to the side of comets or to the side of meteorites.
The study of meteorites on Earth, coming mainly from the main belt of asteroids, has made it possible to establish that the D/H ratio averages about 140 ppm, while this ratio, if you look at it, in some comets was found to be between 150 and 300 ppm. Since it’s about 150 ppm on Earth, the comet hypothesis has been disproved, or at least comets would be far from the main source of water on Earth.
Ryugu’s analyzes therefore support the asteroid hypothesis.
The solar system is a laboratory for studying the formation of giant planets and the origin of life that can be used in conjunction with the rest of the observable universe for the same purpose. MOJO: Modeling the Origin of JOvian planets is a research project that has resulted in a series of videos presenting the theory of the origin of the solar system, and in particular the gas giants, by two renowned specialists, Alessandro Morbidelli and Sean Raymond. For a fairly accurate French translation, click the white rectangle at the bottom right. Then the English subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose French © Laurence Honnorat
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