NASA space telescope sees comet 3I/ATLAS dramatically flare as interstellar visitor exits solar system

New observations from a NASA space telescope show comet 3I/ATLAS brightened sharply after its closest approach to the Sun, offering scientists a rare look at how a fast-moving object on an interstellar trajectory responds to increasing and then fading solar heat.

The post-perihelion flare was detected as the comet headed outward, when most comets gradually dim as they cool and solar radiation weakens. Researchers said the behavior points to rapid changes in the comet’s surface and its surrounding coma of gas and dust, and it may help constrain the composition and structure of an object that likely formed around another star.

A sudden brightening after perihelion

NASA’s telescope data indicate comet 3I/ATLAS increased in brightness in a comparatively short period as it moved away from the Sun. Such a flare is typically linked to an abrupt rise in activity—either from fresh volatile material becoming exposed, a fragmenting event, or a surge in dust release that increases the amount of sunlight the coma reflects.

Because the comet is already receding, astronomers have limited time to gather follow-up measurements before it becomes too faint for many instruments. The new observations provide time-stamped evidence that the comet’s activity did not simply peak at perihelion and subside, but instead underwent at least one notable change after its closest solar pass.

What the flare suggests about the comet’s makeup

Scientists use brightness changes as a practical proxy for physical processes that are difficult to observe directly at large distances. A flare can signal that sunlight and heat penetrated a fragile surface layer, opening vents that release gas and loft dust. It can also result from a partial breakup, which multiplies the total reflecting area as smaller pieces and fine grains spread outward.

For an interstellar visitor, these signatures are particularly valuable. If comet 3I/ATLAS carries ices or minerals that differ from those commonly seen in solar-system comets, the timing and intensity of its outgassing can offer clues to its thermal properties—how quickly it heats, how insulating its crust is, and how easily internal volatiles escape once the surface is disturbed.

Why interstellar comets are a high-value target

Comet 3I/ATLAS is being tracked as an interstellar object—an inbound body that is not gravitationally bound to the Sun and will continue outward to interstellar space. Such objects are thought to be ejected from their home planetary systems early in their histories, turning them into natural samples of distant environments.

Each interstellar detection is rare, and each provides a different kind of laboratory. Unlike most long-period comets from the solar system’s outer reservoir, an interstellar comet can preserve chemical and physical records that reflect different star-forming conditions. Even modest improvements in measurement—brightness evolution, coma development, and dust production—can help refine models of planet formation and small-body evolution beyond the Sun’s neighborhood.

How telescopes read activity from far away

NASA’s space-based observatories can track faint changes in light without the atmospheric interference that complicates some ground observations. By repeatedly measuring the comet’s brightness and comparing it across observing windows, scientists can infer whether the coma is expanding, whether dust production is increasing, and whether any changes occur that are too fast to be explained by distance alone.

In comet studies, the key question is what is driving the brightness: reflected sunlight from dust grains, emission from gas species, or a mix of both. A flare after perihelion can indicate that dust became temporarily dominant—either because gas release intensified and carried more dust into space, or because a surface event exposed fine material that efficiently scatters sunlight.

What researchers will look for next

Follow-up observations will aim to determine whether the flare was a one-time outburst or part of a longer, episodic pattern. If the comet continues to show uneven activity, it may imply a patchy surface with distinct reservoirs of volatiles that become active as illumination and heating angles change along its outbound path.

Scientists will also compare the comet’s behavior with that of better-studied solar-system comets that have shown post-perihelion outbursts. Similarities could suggest common physical mechanisms—such as crust cracking or delayed heating of subsurface layers—while differences could point to unusual composition or structural weakness consistent with an object shaped in another planetary system.

Scientific value as the comet fades

As comet 3I/ATLAS exits the inner solar system, its fading brightness will steadily reduce the amount of detail that telescopes can extract. Still, even a short set of high-quality measurements during this outbound phase can anchor models of its dust production and help estimate the size distribution of particles in its coma.

Those estimates matter because dust and gas activity influence how the comet’s orbit appears when measured precisely. Outgassing can provide small thrusts that slightly alter a comet’s trajectory. For an interstellar object, accurately accounting for such non-gravitational effects helps scientists reconstruct its path through the solar system and better understand the forces acting on it during its brief visit.

Disclaimer: This report is based on publicly available information from NASA-related observations and space-science reporting. Some parameters may be refined as additional data and peer-reviewed analyses become available.