XRISM Makes History: JAXA Detects the First-Ever X-Rays from Interstellar Object 3I/ATLAS
- ACIMA WORLD NEWS 編集部
- Dec 10, 2025
- 3 min read
ACIMA WORLD NEWS Editorial Team
December 10, 2025
Japan’s X-ray astronomy satellite XRISM, developed by JAXA in collaboration with NASA, has achieved a groundbreaking milestone:the world’s first X-ray detection from an interstellar object, 3I/ATLAS.
Using its wide-field soft X-ray imager Xtend, XRISM captured a faint X-ray glow stretching nearly 400,000 kilometers from the object—an observation that opens a new window into the physics of interstellar bodies.
A Historic First: X-rays Detected from an Interstellar Visitor
From November 26 to 28, 2025, XRISM conducted a 17-hour Target of Opportunity observation of 3I/ATLAS. Xtend successfully imaged a vast 3-million-kilometer field, revealing a subtle X-ray halo surrounding the interstellar object.
Before this detection, no X-rays had been confirmed from 3I/ATLAS. This is the first time an interstellar object has ever been seen glowing in X-rays.
What Produces the X-rays Around 3I/ATLAS?
A leading explanation is the same mechanism observed in Solar System comets:
Charge exchange between the solar wind and the gas plume around the object.
This occurs when highly charged solar wind ions interact with neutral atoms in the surrounding gas, producing characteristic X-ray emission. Xtend’s spectrum reveals enhancements in carbon, nitrogen, and oxygen—classic signatures of this process.
These findings are consistent with earlier observations by NASA’s SPHEREx and the James Webb Space Telescope, which detected a large gas plume around 3I/ATLAS in August 2025.
Why XRISM Was Crucial
XRISM cannot observe regions too close to the Sun and must maintain a separation of at least 60 degrees. The observation window opened only after 3I/ATLAS re-emerged from behind the Sun in late November.
During the observation, the object drifted across Virgo, requiring 14 satellite re-pointings to keep it centered within Xtend’s wide field of view.
This precise tracking is what enabled the historic detection.
Japan’s XRISM Leads the Global Effort
The fact that JAXA’s XRISM captured the first X-ray signature of an interstellar object is a significant achievement for Japanese astronomy and a major contribution to global space science.
With 3I/ATLAS currently the most studied object in the Solar System, XRISM’s data will play a central role in the scientific discussions ahead.
What Comes Next?
Astronomers worldwide will now examine the XRISM dataset for:
deviations from typical charge-exchange signatures
extended structures in the X-ray halo
unexpected spectral features
If anything unusual is found, it may reshape our understanding of how interstellar objects interact with the heliosphere.
ACIMA’s View
This detection is more than a technical milestone.
It further supports growing evidence that 3I/ATLAS is undergoing large-scale gas release, consistent with earlier infrared and UV observations.
The combination of:
Hubble’s structural imaging
Webb and SPHEREx’s gas detections
STEREO and SOHO’s dust signatures
and XRISM’s X-ray halo
contributes to one of the most comprehensive multi-wavelength portraits ever assembled for an interstellar object.
ACIMA will continue to follow primary sources and provide clear, accurate updates as new data emerges.
What Do You Think About XRISM’s Discovery?
We’d love to hear your thoughts.
What does this first X-ray detection mean for our understanding of interstellar visitors?
Share your comments and impressions with us.
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