Comet 3I/ATLAS’ upcoming encounter with the sun could change it in big ways — Space photo of the week

Even as a brilliant, naked-eye comet slices through Earth’s sky (cheers, Comet Lemmon!), the most famous object in the solar system right now is hidden on the far side of the sun: the interstellar comet 3I/ATLAS.

This alien visitor, which most astronomers believe to be a comet originating from an unknown star system far beyond our own, is only the third interstellar object ever detected in our solar system. It is the largest, fastest-moving, and quite likely the oldest interstellar object ever seen.

Though it was just confirmed by NASA in early July, the freewheeling ball of ice and dust is already nearing the halfway point on its tour of our solar system. This Wednesday (Oct. 29), 3I/ATLAS will reach perihelion — its closest point to the sun — before beginning its months-long departure from our cosmic neighborhood.

We’ll miss our interstellar friend, but at least we’ll always have the photos. The image above, captured Aug. 27 by the National Science Foundation-operated Gemini South telescope in Chile, may be the clearest image we have so far. As 3I/ATLAS zooms closer to the sun, radiation from our star heats the ice on the comet’s body (its nucleus), causing geysers of gas and dust to shoot outward and form a glowing plume (a coma) around it. Radiation pressure from our star’s unrelenting solar wind pushes this material into a long, prominent tail angled away from the sun.