{"id":798937,"date":"2025-10-30T08:03:29","date_gmt":"2025-10-30T13:03:29","guid":{"rendered":"https:\/\/spaceweekly.com\/?p=798937"},"modified":"2025-10-30T08:03:29","modified_gmt":"2025-10-30T13:03:29","slug":"interstellar-object-3i-atlas-shows-rapid-brightening-near-perihelion","status":"publish","type":"post","link":"https:\/\/spaceweekly.com\/?p=798937","title":{"rendered":"Interstellar object 3I\/ATLAS shows rapid brightening near perihelion"},"content":{"rendered":"


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Interstellar object 3I\/ATLAS (C\/2025 N1) reached perihelion on October 29, at about 1.36 AU from the Sun. The event made it temporarily invisible from Earth as it entered solar conjunction on October 21, but this same geometry placed it within the fields of view of several space-based solar instruments that continued to record its activity.<\/p>\n

A rapid-analysis preprint by Q. Zhang and K. Dattams compiled images from STEREO-A, SOHO, and GOES-19. STEREO-A\u2019s SECCHI suite (HI1 and COR2 cameras) provided wide-field imaging, while SOHO\u2019s LASCO C3 and GOES-19\u2019s Compact CORonagraph (CCOR-1) supplied additional coverage during September and October. The preprint is preliminary and has not yet undergone peer review.<\/p>\n

Stacked frames from these instruments show 3I\/ATLAS surrounded by an extended glow about 300 000 km (186 400 miles) across in CCOR-1 images. An equivalent stack centred on a nearby star was used as a control to verify the signal. All frames were aligned with north up and annotated with the object\u2019s direction of motion and Sun-facing orientation.<\/p>\n

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New images of 3I\/ATLAS prior to perihelion from various instruments. Left panel: Stack of all CCOR-1 frames of 3I\/ATLAS (top), and an equivalent stack centered on a nearby star on the same frames (bottom). Right panel: Similar stacks of all HI1 (top), COR2 (middle), and LASCO C3 Clear (bottom) frames. All stacks are aligned with north up. The heliocentric velocity (+v), and sunward (\u2299) or anti-sunward (\u2212\u2299) directions are labeled. Credit: Q. Zhang and K. Dattams<\/figcaption><\/figure>\n<\/div>\n

Astrophysicist Avi Loeb commented on the same dataset, writing that \u201cthis unfavorable geometry of opposition from Earth \u2014 a possible hint of design \u2014 placed 3I\/ATLAS within the fields of view of several space-based solar coronagraphs and heliospheric imagers.\u201d <\/p>\n

Loeb added that the images \u201creveal rapid brightening and a colour bluer than the Sun,\u201d contrasting with earlier redder ground-based observations. He suggested that emission from gas or dust may dominate the visible light. The phrase \u201cpossible hint of design\u201d is Loeb\u2019s interpretation and not part of the scientific analysis.<\/p>\n

The coma scale reported by CCOR-1 is close to that seen by the SPHEREx space observatory between August 8 and 12, which detected a plume of carbon dioxide about 348 000 kilometres in radius. SPHEREx data indicated that carbon dioxide was the dominant volatile, while JWST observations on August 6 showed a CO2<\/sub>\/H2<\/sub>O ratio near eight to one. <\/p>\n

These compositions differ from most Solar System comets, where water vapour usually dominates. Both the SPHEREx and JWST results are mission releases and await formal peer review.<\/p>\n

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For the past few days, the interstellar comet 3I\/ATLAS has been displaying a blue-green gas coma measuring 2.5 arcminutes across. A short tail was also visible on September 9 when photographed with the 12″\/f-3.6 astrograph in Namibia. image Gerald Rhemann, Michael J\u00e4ger pic.twitter.com\/N3rXvYn3N8<\/a><\/p>\n

\u2014 Michael J\u00e4ger (@Komet123Jager) September 10, 2025<\/a><\/p><\/blockquote>\n<\/div>\n<\/figure>\n

After perihelion, 3I\/ATLAS is expected to reappear in the morning sky by mid-November 2025. Its closest approach to Earth will be on December 19 at about 1.8 AU.<\/p>\n

Observations with Hubble, JWST, and major ground-based telescopes are planned to measure its brightness and spectrum as it recedes. Researchers expect that it may emerge from perihelion slightly brighter than before.<\/p>\n

The authors of the new study write that the reason for 3I\/ATLAS\u2019s strong activity, which surpasses that of most Oort-cloud comets at comparable distances, remains unknown. Updated analyses will follow as post-perihelion data become available.<\/p>\n