The X-Ray Imaging and Spectroscopy Mission (XRISM) observed the interstellar comet 3I/ATLAS for 17 hours between 26–28 November 2025.
3I/ATLAS is the first interstellar comet to have been imaged in X-ray light. Whether interstellar comets shine in X-rays as we are used to from comets originating within the Solar System, or whether they exhibit entirely different characteristics, has remained a long-standing mystery.
The X-ray image of the comet you see here was captured by XRISM’s soft X-ray telescope Xtend. The field of view covers a region of about 3 million km², revealing X-rays coming from a region of around 400 000 km around the comet nucleus. This could be caused by a diffuse cloud of gas surrounding the comet, although it requires further analysis.
XRISM’s X-ray image can be compared to that of the European Space Agency’s XMM-Newton, which also saw a diffuse X-ray glow around the comet.
These X-rays can come from the interaction of the solar wind with gases from the comet, such as water vapour, carbon dioxide, or carbon monoxide. Analysis of XRISM’s data from around the comet nucleus shows signs of carbon, nitrogen and oxygen.
Read the full XRISM web story here.
For the latest updates and FAQs related to comet 3I/ATLAS, see esa.int/3IATLAS.
XRISM (pronounced krizz-em) is a mission led by the Japan Aerospace Exploration Agency (JAXA) in partnership with NASA and ESA. It carries two instruments: an X-ray calorimeter called Resolve capable of measuring the energy of individual X-ray photons to produce a spectrum at unprecedented level of ‘energy resolution’ (the capability of an instrument to distinguish the X-ray ‘colours’), and a large field-of-view X-ray CCD camera to image the surrounding field called Xtend.
[Image description: This image shows an X-ray view of interstellar comet 3I/ATLAS, captured by the JAXA-led XRISM spacecraft. Against a black background, purple-to-green blobs appear throughout the image. Around the centre-right of view, a larger, bright green blob stands out – this is the X-ray light coming from near the comet’s nucleus. A red arrow labelled “Sun direction” points left, and a yellow arrow labelled “comet motion” points to the right. At the bottom, a scale marker reads “38.5 arcmin ~ 3,000,000 km”, while a white circle labelled “r = 5 arcmin ~ 400,000 km” surrounds the bright comet blob.]