Astronomers Discover Third-Ever Interstellar Object: 3I/ATLAS
After the interstellar asteroid 1i / ʻoumuamua and the interstellar comet 2i / Borisov, 3i / Atlas is the third object and the second comet from the outside of the confirmed solar system.
This image, taken with the Itelescope.net T72 telescope in Rio Hurtado, Chile, July 2, 2025, shows the interstellar Comet 3i / Atlas. Image credit: Filipp Romanov / CC by-SA 4.0.
The 3i / Atlas was discovered by the telescope of the Atlas study funded by the ATLA (asteroid with terrestrial impact) in Rio Hurtado, Chile, on July 1, 2025.
Arriving from the management of the Sagittarius constellation, the interstellar comet is currently located around 670 million km (420 million miles).
“Since this first report, observations before the discovery have been gathered from the archives of three different Atlas telescopes from around the world and the transitional installation of Zwicky at the Palomar Observatory in the County of San Diego, California,” NASA astronomers wrote in a press release.
“These” pre-discovery “observations date back to June 14, 2025.”
Also known as C / 2025 N1 (Atlas) and A11PL3Z, 3i / Atlas is currently around 4.5 UA (670 million km or 416 million miles) of the sun.
The comet does not represent any threat to the earth and will remain at a distance of at least 1.6 AU (240 million km or 150 million miles).
He will reach his approach closest to the sun around October 30, 2025, at a distance of 1.4 AUs (210 million km or 130 million miles) – just inside the Mars orbit.
Its size and physical properties are studied by astronomers around the world.
This diagram shows the 3i / atlas trajectory when it goes through the solar system. Image credit: NASA / JPL-CALTECH.
“If the brightness of 3i / Atlas comes from the reflect of the sun to the Albédo typical of the order of 10%, then its diameter of 20 km is approximately 100-200 times larger than the estimated length of` Oumamua (and more than a thousand times larger than the “Oumuamua’s Width) and about 50 to 100 times larger than the plan of the committee”, the head of Comet Borisov, “by Black Hole Initiative at Harvard University and director of the Institute of Theory and Calculation at the Harvard-Smithsonian Center for Astrophysics, wrote in his blog.
“If the three objects are rocks, the mass of 3i / Atlas is greater than ten million times greater than that of ‘Oumua and at least one hundred thousand times larger than the central mass of Borisov.”
“This is surprising because we expect high mass objects to be much rarer.”
“Based on the data on the main asteroid belt of the solar system, millions of objects like ‘Oumamua for each object on the mass scale of 3i / Atlas.”
3i / Atlas should remain visible for the ground telescopes until September 2025, after which it will be too close to the sun to observe.
It should reappear on the other side of the sun in early December, allowing renewed observations.
“Based on its movement management, 3i / Atlas seems to come on a retrograde orbit with an inclination of 175 degrees compared to the orbital plane of the earth from the thin disc of the stars in the galaxy of the Milky Way,” wrote Professor Loeb.
“In the coming months, we will learn much more about the properties of 3i / Atlas on the basis of the data of several ground telescopes, including the NSF / Doe Vera C. Rubin observatory in Chile, as well as NASA / ESA / CSA James Webb Space Telescope.”
