Interstellar comet 3I/ATLAS is now on its way out of our solar system, never to return. The comet was only the third-ever detected object to originate from outside our solar system. Traveling at high speeds, it looped around the sun within 1.5 AU (one AU, or astronomical unit, is the distance between Earth and the sun) in October 2025; as of April, it is now past the orbit of Jupiter on its way out of the solar system.

3I/ATLAS is over a kilometer wide and is made up of dust and ices from the far-off planetary system where it originated. Using the advanced instrumentation of the James Webb Space Telescope (JWST), Caltech researchers examined the mid-infrared signatures (wavelengths of light 10 times longer than those humans see) that emitted from 3I/ATLAS as it approached the sun in an effort to understand the distant environment in which the comet formed. The paper is published in The Astrophysical Journal Letters.

“It’s a very interesting object,” says Caltech graduate student Matthew Belyakov, lead author on the new paper. “It has been traveling through the galaxy for at least a billion years. The high speed at which it flew past us gave just a narrow window to study it.”