2023-11-01 19:13:01
The flyby of Ceres, the largest object in the asteroid belt, between Mars and Jupiter, by the Dawn probe made it possible to detect the presence of complex organic molecules there. Knowing that the dwarf planet may have once hosted an ocean of liquid water, scientists believe that it may once have had conditions conducive to the appearance of life. The origin of these organic molecules on the surface of Ceres is the subject of much research.
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[EN VIDÉO] Ceres: discover the dwarf planet at 360° The dwarf planet closest to us, Ceres, has a multitude of white spots…
At the boundary between the inner Solar System and the outer Solar System, between the orbits of Mars and Jupiter, billions of small celestial bodies orbit, whose sizes can vary from millimeters to kilometers. They constitute the main belt, or asteroid belt, formed regarding 4.6 billion years ago by asteroids that did not aggregate into planets. But one object in the main belt stands out clearly from the others, notably by its size: it is Ceres, the only dwarf planet in the main belt. With its radius of approximately 476 kilometers, Ceres alone represents almost a third of the mass of the main belt. Presenting a large quantity of water ice on its surface, it is also the only spherical object in the asteroid belt.
Discovered in 1801, the dwarf planet has recently been the subject of numerous studies, because scientists believe that it is a protoplanet, still retaining characteristics unchanged since the formation of our Solar System. Scientists’ curiosity regarding this celestial body has been further aroused since the discovery of the presence of hydrated materials on its surface, suggesting the presence of a significant quantity of water in its interior, and of a possible ocean. underground.
Revealing in situ observations
In order to unravel the mysteries of the dwarf planet, the American Space Agency (Nasa) launched its Dawn probe in 2007, designed to closely observe Ceres as well as the asteroid Vesta, which also evolves in the asteroid belt. Equipped in particular with a spectrometer, which makes it possible to remotely determine the chemical composition of the surfaces observed, the main objective of the probe was to help understand the processes at work during the formation of the Solar System.
After its observations of the asteroid Vesta, the probe transited towards Ceres, around which it placed itself in orbit in 2015. And the observations of the dwarf planet led to surprising results: the probe detected on the surface of Ceres the presence of complex organic molecules. Combined with the idea that the dwarf planet might harbor an ocean world within it, these results indicate that Ceres may once have housed the ingredients necessary for the emergence of life as we know it. The Dawn probe is no longer active today, and has become a “passive” satellite of Ceres.
An origin of these organic compounds still debated
The organic compounds detected on the surface of Ceres are called aliphatic: they are hydrocarbons (composed only of hydrogen and carbon atoms), whose carbon chains have linear structures (for example, methane). Since their discovery in 2017, the reasons for their presence on the dwarf planet have been the subject of numerous research and hypotheses, leading to generally two distinct schools.
Some scientists believe that these compounds were brought to Ceres by impacts of comets or other celestial bodies rich in organic compounds, while others propose that these compounds were formed by the alteration of the compounds initially present by the action of salt water. In any case, given the numerous impacts that the dwarf planet has suffered (and still undergoes), the evolution of these organic molecules on the surface of Ceres is very probably closely linked to the almost omnipresent impacts which have shaped its surface, d especially since the first organic compounds detected were located near an impact crater.
The fruit of several processes?
But a recent study, presented on October 17 at the Geological Society of America (GSA), tends to show that the appearance of these organic molecules would in fact be the result of several distinct processes and phenomena, mixing the two major hypotheses previously stated. In order to determine the origin of these organic compounds, the authors combined the data collected by the spectrometer and those measured by the camera, on board the probe, allowing them to draw up a precise map of the presence of organic compounds on the surface of the dwarf planet. At the same time, they simulated impact conditions typical of Ceres, with impact speeds ranging from 2 to 6 km/s and impact angles varying between 15 and 90 degrees from the horizontal.
Their results thus indicate a strong spatial correlation between the presence of organic compounds and the location of impact structures, as well as between the presence of organic compounds and the presence of minerals, such as carbonates, testifying to the presence of water. Although the origin of these compounds remains little understood, scientists are confident regarding a significant part of an endogenous origin: they estimate that these organic compounds might have formed on Ceres, probably thanks to the presence of water. This conclusion points to a plausible existence of a large reservoir of organic compounds in the bowels of the dwarf planet, motivating its interest in the search for extraterrestrial life.
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