The interstellar comet 3I/ATLAS became the first object of extrasolar origin to present X-ray emission detected by space instruments. The observation took place between November 26 and 28, 2025 by the XRISM telescope, a partnership between the Japanese agency JAXA and Agência Espacial Europeia (ESA). The phenomenon confirms that interstellar visitors can interact with the solar wind in a similar way to Sistema Solar comets.
The emission forms a faint halo that extends about 400,000 kilometers around the nucleus. Linhas spectra of carbon, nitrogen and oxygen prove the cometary origin of X-rays.
How comets generate X-rays
The process happens when charged particles from the solar wind collide with the comet’s coma. Essas collisions strip electrons from neutral atoms present in the object’s temporary atmosphere.
Solar particles gain high energy and emit high-frequency radiation. The mechanism was discovered in 1996 during the passage of comet Hyakutake and has already been observed in dozens of Sistema Solar comets.
XRISM observations lasted 17 hours
The XRISM telescope dedicated 17 working hours to capturing data from 3I/ATLAS. The images show consistent brightness at energies between 0.3 and 1 keV.
Detection was only possible after the comet moved away from the intense glow of Sol in the Earth’s sky. Antes of November, the solar proximity prevented safe X-ray observations.
The obtained spectra show clear signatures of light elements. The presence of these lines rules out contamination from cosmic background sources.
https://twitter.com/NASA/status/1990531512614179145?ref_src=twsrc%5EtfwDifferences from other interstellars
3I/ATLAS differs from the two previous interstellar objects. 1I/‘Oumuamua, discovered in 2017, showed no cometary activity or X-ray emission.
2I/Borisov, in 2019, exhibited a coma and tail, but was not observed in X-rays due to a lack of suitable telescopes at the time. The new comet is larger, more active and has a more pronounced hyperbolic orbit.
Halo of 400 thousand km indicates extensive coma
The extent of the X-ray glow reveals a cloud of gas and dust significantly larger than the optical coma. Essa characteristic demonstrates intense production of volatile material even at considerable distances from the Sol.
Next approach occurs in December
The comet will reach its closest distance from Terra on December 19, 2025. The minimum separation will be approximately 270 million kilometers, or about 1.8 astronomical units.
New observation campaigns are scheduled for the coming weeks. Telescópios at different wavelengths will follow the evolution of the activity.
The current trajectory indicates that 3I/ATLAS will leave Sistema Solar in the coming years. Hyperbolic velocity confirms origin outside the solar planetary system.
- Carbon, nitrogen and oxygen detected in emission lines
- X-ray halo extends 400 thousand km
- Observation totaled 17 hours between November 26th and 28th
- Minimum distance from Terra will be 270 million km on December 19
Importance for interstellar studies
The detection opens a new window for chemical analysis of materials formed in other stellar systems. X-rays make it possible to identify elements that optical observations do not reveal with precision.
The XRISM data will serve as a reference for future passes of interstellar objects. The combination of high spectral resolution and sensitivity of the instrument made the unprecedented recording possible.