Interstellar Comet 3I/ATLAS Brightens Rapidly near Perihelion

Interstellar comet 3I/ATLAS brightened markedly as it swung behind the sun, with researchers and skilled amateurs using multiple spacecraft to follow its progress up to perihelion on Thursday, 29 October. Though out of direct terrestrial view while near the sun, the object’s activity was captured in coronagraph imagery and heliophysics missions designed to monitor the solar environment.

Spacecraft tracking and geometry

Observers leveraged space-based assets to overcome the comet’s solar glare. With 3I/ATLAS hidden from ground-based telescopes, coronagraphs and wide-field imagers traced its motion across the inner heliosphere. The behind-the-sun geometry temporarily prevented visual follow-up from Earth, but spacecraft vantage points provided continuous coverage until it moved out of instrument fields of view.

Rapid brightening and expected peak

Analyses indicated a swift increase in brightness ahead of perihelion. Estimates suggested a rise from roughly magnitude ~11 to about magnitude ~9 near closest approach to the sun—still beyond naked-eye limits but reachable for capable backyard telescopes once viewing geometry improves. Such brightening is consistent with escalating dust and gas release as solar heating intensifies volatile activity on the nucleus.

What the instruments saw

Amateur astronomer Worachate Boonplod detected 3I/ATLAS in imagery from NOAA’s GOES-19 using the CCOR-1 coronagraph, noting it remained visible in that field until 24 October. Parallel tracking occurred with NASA–ESA’s SOHO (LASCO C3) up to 26 October, while NASA’s PUNCH mission—four smallsats studying the corona–heliosphere interface—also followed the comet. Coronagraphs block the sun’s disc to reveal faint structures around it, making them ideal for monitoring comets in otherwise blinding conditions.

Exam Oriented Facts

• 3I/ATLAS is an interstellar comet, meaning it originated outside our solar system.
• Perihelion occurred on Thursday, 29 October, during a behind-the-sun passage.
• Spacecraft used included GOES-19 (CCOR-1), SOHO (LASCO C3) and NASA’s PUNCH mission.
• Estimated brightening: ~mag 11 to ~mag 9 near perihelion.

Visibility prospects and scientific value

As the comet re-emerges from solar conjunction, prospects for ground-based observation improve, subject to elongation, solar glare and local twilight. Small telescopes under dark skies may record a condensed coma and developing tail if activity sustains. Scientifically, continued monitoring can probe dust-to-gas ratios, outflow speeds and grain size distribution, offering a rare comparative dataset alongside the only other confirmed interstellar visitors seen from Earth.
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