An object from outside the solar system has been spotted crossing it at full speed. This is the third interstellar visitor ever detected, astronomers confirmed on Wednesday.
This object, probably the largest ever observed, has been classified as comet by the center of minor planets of the International Astronomical Union (IAU-MPC).
Its aspect “suggests that it is mainly ice rather than rock”, explains Jonathan McDowell, astronomer in the center of astrophysics of Harvard-Smithsonian.
“He does not present a risk of collision with the earth,” said the manager of the planetary defense From the European Space Agency (ESA) Richard Moissl: “He will fly deep into the solar system, just passing inside the Mars orbit.”
At its point closest to our planet, it will be 240 million kilometers from us, more than a half the distance between the earth and the sun. He will then be hidden behind our star.
Astronomers are still specifying their calculations, but its speed seems to exceed 60 kilometers per second, more than 200,000 km/h. This means that it is not linked to the orbit of the sun.
Extragalactique
Its trajectory also “indicates that it is not in orbit around the sun, but comes from the interstellar space and will return there,” according to Richard Moissl. This remainder of another stellar system transports with it indices with regard to the formation of other worlds far beyond ours (Read box). This is the opportunity to study something really extraterrestrial and extragalactic …
If this active comet warms up sufficiently when approaching our star, it could start to sublimate: a process where frozen gases transform directly into vapor, causing particles of dust and ice in space to form an incandescent tail.
Based in Hawaii, the project ATLAS Asteroid surveillance funded by NASA, discovered the object on July 1, writes the American astronomer David Rankin on the Bluesky social network. Named at first A11Pl3z, its final designation is 3i/atlas (or C/2025 N1).
Astronomers of the professional environment, as well as amateurs from around the world, then searched in the data recorded by the telescopes, reconstructing its trajectory since June 14, discovering it extremely hyperbolic: a clear sign that this ball of rock and ice will never return.
The size of this comet is currently estimated 10 to 20 kilometers in diameter. But it could be smaller if it is well composed of ice, a material that more reflects light.
Observable until next year
“She will shine more and more and approach the sun until the end of October, and will still be observable (by telescope) until next year,” explains Richard Moissl.
![The trajectories through the solar system of Oumuamua (in red) and 2i/Borisov (in yellow). [Wikimedia - Tony873004/CC 4.0]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw== "The trajectories through the solar system of Oumuamua (in red) and 2i/Borisov (in yellow). [Wikimedia - Tony873004/CC 4.0]")
It is the third object never observed from the interstellar space: hence the “3” and the “I” in its name.
The first, Oumaumua, had been detected in 2017. He was so strange that at least a renowned scientist, Avi Loeb, had finally convinced himself that it was an extraterrestrial vessel – his theory has since been denied by research.
The second interstellar racing car, 2i/Borisov, had been detected on August 30, 2019: it was also a comet, relaxing a large concentration of carbon monoxide, discovered by a Ukrainian amateur astronomer from an observatory in Crimea.
This new visitor seems to “move much faster than the first two extra-solar objects that had been discovered”, remarks Mark Norris, astronomer at the British University of Central Lancashire.
The object is currently almost at the same distance from the earth as Jupiter, he added.
Stéphanie Jaquet and ATS
