Scientists have watched in fascination as interstellar object 3I/ATLAS, only the third of its kind spotted in the solar system so far, hurtled past several planets and made its closest pass of the Sun in October.
And as it’s on its way out, likely never to be seen again, scientists are still making astonishing new findings about the extremely rare visitor. For instance, it appears to have started spewing huge amounts of water into space.
Its closest pass of the Sun really kicked things off, as evidenced in observations by NASA’s SPHEREx near-infrared space observatory, which was launched a mere half a year before its solar flyby in late October.
“Comet 3I/ATLAS was full-on erupting into space in December 2025, after its close flyby of the Sun, causing it to significantly brighten,” said Johns Hopkins astronomer Carey Lisse, lead author of a recent paper about the SPHEREx findings, in a NASA statement. “Even water ice was quickly sublimating into gas in interplanetary space.”
The release also dislodged even more intriguing materials that potentially date back billions of years.
“And since comets consist of about one-third bulk water ice, it was releasing an abundance of new, carbon-rich material that had remained locked in ice deep below the surface,” Lisse added. “We are now seeing the usual range of early solar system materials, including organic molecules, soot, and rock dust, that are typically emitted by a comet.”
The SPHEREx observations don’t look quite like you’d expect with a regular comet, though.
“The comet has spent ages traversing interstellar space, being bombarded by highly energetic cosmic rays, and has likely formed a crust that’s been processed by that radiation,” SPHEREx instrument scientist Phil Korngut said in a statement. “But now that the Sun’s energy has had time to penetrate deep into the comet, the pristine ices below the surface are warming up and erupting, releasing a cocktail of chemicals that haven’t been exposed to space for billions of years.”
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