3I/ATLAS was detected on July 1, 2025, by the NASA-funded ATLAS survey telescope in Chile. Its discovery was a result of ATLAS's routine, systematic scanning of the night sky for near-Earth objects. The object was identified as an interstellar object due to its unusual speed and hyperbolic trajectory. "Observations by the James Webb Space Telescope have shown that 3I/ATLAS is unusually rich in carbon dioxide and contains a small amount of water ice, water vapor, carbon monoxide, and carbonyl sulfide." "The comet originated from interstellar space in the direction of the constellation Sagittarius, near the Milky Way's Galactic Center."
It is one of only three interstellar objects which have been detected "interloping" into the solar system. Of the three, 3I/ATLAS is the largest and fastest-moving. Wikipedia's
Interstellar object tells us "There has been speculation that interstellar interlopers observed in the solar system are extraterrestrial spacecraft, but this been[sic] ruled out." But
their 7-year old source states only that there is no evidence that one (1) of the earlier interlopers was an alien spacecraft.
The
trajectory of
3I/ATLAS can be seen at on-line orbit viewers. It moves fast, passing Jupiter's orbit June 9 (with Jupiter near opposite side of orbit), making a very close approach (0.1936 AU) to Mars Oct 3, not approaching Earth or even Earth's orbit, but finally making a very close approach (0.39 AU) to Jupiter March 16 of next year. It comes within 0.6494 AU of Venus on November 3 -- about as close as could be achieved, given that it never gets as close as 1.356 AU to the Sun.
For those conspiring about a possible alien probe, there are several reasons to be suspicious:
- The object's trajectory is tilted 175° (retrograde and inclined 5°) with respect to the ecliptic. Randomly an object has only a 2.8% chance of an inclination so good for its viewing our system. (OTOH, I suppose ssuch a trajectory would be best for OU chanes of even detecting IT.)
- The object was aimed close to the Sun, and crossed the ecliptic at approximately its closest approach to Sun. I suppose this was no coincidence, just Sun's gravity.
- The VERY close approaches to Mars and Jupiter (and even Venus) i-- all still in the future -- are a priori very much odds-against. Even if we agree that it is NOT an alien probe, it is remarkable that the largest and fastest interstellar interloper detected so far has "close encounters" about 1 million-to-one odds-against.
- Comets have "tail" pointing away from Sun, but this object has a tail pointing toward Sun. (This has explanation, but I don't fully understand.)
- Another puzzling detail I've forgotten.
Don't be disappointed if 3I/ATLAS is not an alien probe hoping to save us. We may be beyond salvation anyway.