3I/ATLAS Shock: ESA XMM-Newton Telescope Detects Mysterious X-Ray Glow From Alien Comet

3I/ATLAS, a rare visitor from beyond the solar system, has revealed an unexpected signal.

Scientists at the European Space Agency (ESA) have confirmed that their XMM-Newton space telescope detected a faint X-ray glow from the interstellar object known as 3I/ATLAS.

The discovery was made in early December 2025 as the comet moved closer to Earth, offering researchers a new way to study how alien objects react to the Sun's influence.

Discovery Details: What XMM-Newton Saw

ESA's XMM-Newton X-ray observatory tracked the 3I/ATLAS comet on 3 December 2025. The observation lasted for around 20 hours, while the comet was roughly 282 to 285 million kilometres away from the spacecraft.

The telescope used its most sensitive instrument, the European Photon Imaging Camera, known as EPIC-pn. The resulting images showed a faint but distinct glow of low-energy X-rays. Red areas marked the emission from the comet, while blue regions showed largely empty space around it.

ESA explained that the detection itself was not unexpected. In an official statement, the agency said: 'Astronomers expected to see this glow because when gas molecules streaming from the comet collide with the solar wind, they produce X-rays.'

How a Comet Produces X-Rays

Comets shine in visible light when sunlight reflects off dust and gas. X-rays, however, tell a different story. They form when charged particles from the Sun, known as the solar wind, crash into gases escaping from a comet's nucleus.

This process has been observed before in comets from the solar system. What makes 3I/ATLAS different is its origin. This is the first time scientists have studied this mechanism in such detail in an interstellar comet.

'This makes X-ray observations a powerful tool. They allow scientists to detect and study gases that other instruments can't easily spot,' said ESA.

A Visitor Unlike Any Other

Data collected across multiple observatories show that the 3I/ATLAS comet has an unusual chemical composition. It contains high levels of carbon dioxide but relatively little water, producing a CO2-to-water ratio rarely seen in local comets.

Astronomers have also identified carbon monoxide and traces of atomic nickel vapour. Nickel is rarely detected in gaseous form in comets, suggesting the object formed in a very different environment from most bodies in the solar system.

These findings point to a cold or chemically distinct birthplace around another star.

An Ancient, Weathered Traveller

Researchers believe 3I/ATLAS may be billions of years old. It likely formed early in a distant planetary system before being ejected into interstellar space. During its long journey, the comet's surface was probably exposed to galactic cosmic rays for extended periods.

This exposure may have altered its outer layers. Scientists think the current activity could be caused by fractures in that surface, allowing fresher material from the interior to escape for the first time.

Jets, Dust, and Rotation

High-resolution images show jets of gas and dust streaming from the nucleus of the 3I/ATLAS comet. Polarimetric data also suggest that the dust grains in its coma differ from those seen in most solar-system comets.

The jets appear to change over time in a pattern consistent with a rotation period of about 15 to 16 hours. While this rotation rate is common among local comets, it is surprising for an object that has spent most of its existence drifting through interstellar space.