At morning twilight on December 13, 2025 (Hawaii-Aleutian Standard Time, HAST), the Faint Object Camera and Spectrograph (FOCAS) mounted on the Subaru Telescope captured images of comet ATLAS (3I/ATLAS; C/2025 N1), which is known to be an interstellar object hailing from outside our Solar System.
Comet ATLAS, discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile on July 1, 2025, is only the third confirmed interstellar object
following 1I/ʻOumuamua (C/2017 U1) and 2I/Borisov (C/2019 Q4). At the time of observation, just before its closest approach to Earth on December 19, it was approximately 270 million kilometers away—about 1.8 times the distance between the Sun and Earth. Although it was a very short observation, the comet tail is clearly visible in the captured images.
Figure 1: Interstellar object 3I/ATLAS (C/2025 N1) captured by FOCAS on the Subaru Telescope. This image was created by combining three different wavelengths: V-band (550 nanometers), R-band (660 nanometers), and I-band (805 nanometers). These wavelengths are depicted in blue, green, and red respectively. Three images with 2-second exposures are stacked in each band. The field of view of the image is 2.4 arcmin × 1.2 arcmin. (Credit: NAOJ)
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