Comet 31/ATLAS, the solar system interloper, has its tail facing the wrong way – aligned directly opposite what one might expect. So it would seem. See for exmple https://dailygalaxy.com/2025/09/interstellar-comet-3i-atlas-tail-sun/ … The tail stretches 56,400 km in length, pointing to the SE. It has a coma, or gas envelope, measuring 18,800 km across, much larger than what was seen back in July. On top of that it is veiled by an enormous carbon dioxide plume that extends 348,000 km. This huge cloud of gas is mostly composed of co2 – with smaller quantities of carbon monoxide and water. This also seems to mostly differ from other comets. These are usually dominated by water – as ice or vapour. The comet nucleus itself is estimated to be 43 km across – based on light flux. These evaluations may change as it gets closer.
Another unusual feature is its trajectory. 31/ATLAS travels along a path closely aligned with the ecliptic plane. Also, spectroscopic data has revealed a lot of nickel but no iron. The same story was at https://spaceweather.com … on September 4th [2025]. They tell us that comets with a lot of co2 have blue tails because of photochemistry.
See also https://www.livescience.com/space/comets/james-webb-telescope-images-reveal-theres-something-strange-with-interstellar-comet-3i-atlas …. and at https://spacweather.com … on September 9th, another image shows the comet as green in colour. These images were taken by sky watchers rather than by big telescopes. Over at https://phys.org/news/2025-09-comet-alien-spaceship-astrophysicist-interstellar.html … we have a Hubble image that shows it clearly as blue. It also tells us this is the result of co2 – probably co2 ice. Interestingly, the last apparition of the Indian god Krishna, dated around 3000BC by traditional numbers, was strongly associated with the colour of blue. Space Weather also mentions that other comets have had a blue appearance. In contrast, https://www.livescience.com/space/comets/new-photos-of-interstellar-comet-3i-atlas-reveal-its-tail-growing-before-our-eyes … where the author of the piece clearly resorts to the mainstream view of comets as heavily water based – and the idea of ice and sublimation as the cause of the growing tail rather than the effects of confronting plasma in the solar wind. No surprise there as the piece also mentions that https://www.space.com … is a sister web site. They also take a mainstream interpretation of everything in space – even if recent observations appear to contradict it. Other links are more interested in the novel features of comet 31/ATLAS. The proof will be in the pudding as the interloper will reach the closest point to the Sun on October 29th.