"That changed in 2017, when interstellar interloper 'Oumuamua arrived: our first known object within the Solar System to originate from outside of it. Then, 2019 brought with it another interstellar object: Borisov, which was larger and appeared much more like a conventional comet than 'Oumuamua did. Starting in early July of 2025, we got our first glimpse of humanity's third identified interstellar interloper: 3I/ATLAS, which initially appeared to be larger, brighter, and faster-moving than either 'Oumuamua or Borisov was."
"Back in early July, the best images we were getting of 3I/ATLAS looked like the image you see above: faint, blurred views of what appeared to be more than a point-like object, but rather an extended source surrounded by a halo-like appearance. With a source such as this, you can still measure the object's velocity and position very well, enabling you to determine its orbital trajectory both past and present: including a very accurate determination of its origin."
Interstellar visitors to the Solar System began with 'Oumuamua in 2017 and Borisov in 2019. In early July 2025, 3I/ATLAS was detected as the third confirmed interstellar interloper and initially appeared larger, brighter, and faster-moving than the prior two. Both ground- and space-based telescopes have observed 3I/ATLAS, showing a faint, diffuse, halo-like coma that obscures the nucleus. Precise astrometry yields reliable orbital trajectories and origin determinations, but the nucleus size remains uncertain because the coma is unresolved. Continued observations as the object approaches perihelion aim to refine its physical properties and behavior.
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