New ultraviolet image of comet 3I/ATLAS could help reveal what it's made of

A NASA spacecraft designed to hunt for signs of extraterrestrial life has turned its lens toward comet 3I/ATLAS — but not for the reason you might think. The spacecraft just happened to be in the right place at the right time.

Zooming through the solar system at an estimated 153,000 mph (246,000 km/h), the beguiling interstellar comet will reach its closest point to Earth overnight tonight (Dec. 18-19). At its closest, 3I/ATLAS will swoop within about 168 million miles (270 million kilometers) of our planet.

It's close enough that amateur astronomers can spot it with a good backyard telescope, though skywatchers should temper their expectations of seeing much more than a speedy green dot. (See astrophotographer Andrew McCarthey's latest image for a preview.)

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Meanwhile, the latest image from NASA — taken with the Europa Clipper spacecraft — cuts the distance to 3I/ATLAS by a third. Snapped on Nov. 6 from a distance of about 102 million miles (164 million km), the new image is the result of seven hours of observations with the craft's Europa Ultraviolet Spectrograph (Europa-UVS) instrument.

Seeing the unseen

Human eyes can't see UV light. But by splitting the observations into their constituent wavelengths and stacking them together, NASA scientists offer a hint of what 3I/ATLAS would look like beyond the visible spectrum. (See also the James Webb telescope's infrared observations and XMM-Newton's X-ray view.)

Clipper happened to be in a prime spot to observe 3I/ATLAS as both objects zoom toward Jupiter; the swift interstellar comet makes its closest approach to the gas giant in March 2026, while Clipper isn't due to arrive there until April 2030.

When it does reach the Jovian neighborhood, Clipper will begin its mission to hunt for signs of extraterrestrial life. The spacecraft's UV instruments will analyze the surface and atmosphere of Europa — one of Jupiter's giant, ice-encrusted moons — and look for geysers carrying chemical clues to the moon's interior. NASA models hint that a liquid water ocean lurks beneath the Europa's crust, which could contain alien life.

An evolving mystery

But the Clipper isn't looking for aliens in this case. (And there's no evidence that 3I/ATLAS is anything other than a natural comet.)

Using the same technology that will ultimately plumb the secrets of Jupiter's moon, Clipper's observations of 3I/ATLAS will be key in analyzing the elements spewing out of the comet and forming the makeshift atmosphere, or coma, around it.

There's no spectroscopic data from Clipper's new UV image yet, but NASA will share its findings as soon as they're available. We do know from prior observations that 3I/ATLAS is rich in carbon dioxide ice, and is releasing diatomic carbon (C₂) gas that gives it the greenish glow seen in recent optical light images.

Until more information rolls in, enjoy this rare close-up view of our solar system's most famous visitor from abroad.