Saturn’s rings may not be that young, their fresh complexion the result of a mechanism that would prevent them from turning brown due to micrometeorite pollution, according to a study published Monday.
Saturn, the gas giant of the solar system, was born with the other planets more than four billion years ago. But its rings are only 100 to 400 million years old according to recent studies, recalls that published in Nature Geoscience.
The estimates are based in particular on the observation that the planet’s rings retain a strong reflective power, even though they are constantly bombarded by micrometeorites which are ultimately supposed to dull their shine.
The bombardment was precisely measured by the Cassini-Huygens probe, which spent thirteen years in orbit around Saturn, until 2017. Despite this, little is still known about its rings.
Observed in the 17th century by the Dutch astronomer Huygens, after Galileo, they form a thin disk, made up essentially of water ice and a few minerals, and extending in several rings up to approximately 80,000 km from the planet.
“One of Cassini’s main conclusions is that the rings should be young because they don’t seem very polluted,” Gustavo Madeira, a postdoctoral fellow at the Institut de Physique du Globe in Paris and co-author of the paper, told AFP. ‘study.
Hence this predominantly grey-yellow hue, which would reflect the fact that the rings “accrete”, as astronomers say, a significant quantity of micrometeorites which dirty the original ice.
Pollution resistance
But the study led by Ryuki Hyodo, a researcher at the Tokyo Institute of Science, suggests that “the apparent youth of Saturn’s rings results from resistance to pollution, rather than indicating a young age of formation “.
The model he developed simulates the impact of micrometeorites on pieces of ice or silica in the rings.
In this scenario, the velocity of the particle is typically 30 km/s, or more than 100,000 km/h. The shock would then release enough energy to vaporize the micrometeorite as well as part of its target.
As for the nanoparticles resulting from the impact, they would be evacuated under the impulse of the planet’s magnetic field, then captured in its atmosphere or released into space.
The phenomenon would thus make it possible to protect the rings from micrometeorite pollution, and to preserve a sort of eternal youth.
The remaining problem is that “for example we do not know the initial composition of Saturn’s rings”, at the time of their formation, notes Gustavo Madeira. “We assume that it was ice, but in fact we know nothing,” he adds.
Planetologists assume that they come from either pieces of comets, asteroids or even ancient moons of Saturn. So much uncertainty means that the debate on the age of the rings is not ready to die down.
To close it, it would ideally be necessary to “collect samples of the rings to analyze their properties”, dreams Mr. Madeira.
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