C/2025 31 (ATLAS) Interstellar Comet

 

Comet/ 2025 31 (ATLAS) Interstellar Comet.
Captured 16-02-2025 from the Jodrell Plank Observatory, Suffolk UK.
Using the Seestar S30 Smart Telescope with Infra Red filter. 60 sec exposures stacked.
Image Credit: Pip Stakkert and Kurt Thrust

Plate Solver animation showing the SDSS (Sloan Digital Sky Survey) view without the comet, overlaid on the same star field with the comet as captured with the Seestar S30. SDSS and Plate Solver Image Credit: Astrometry Net.

Star Map showing he approximate position of Comet C/2025 31 (ATLAS)
on the evening 16_02_2026. Base image Credit: Wikipedia

Enlargement of the Seestar S30 image local to the comet
- faint hint of cometary nucleus and tail?

" Interstellar origin: Comet C/2025 3I/ATLAS is the third confirmed object from outside our Solar System observed by astronomers, after 1I/ʻOumuamua (2017) and 2I/Borisov (2019).

It was first detected on 1 July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes in Chile.

Its orbit is hyperbolic, meaning it’s not gravitationally bound to the Sun and is just passing through.It has passed perihelion, its closest point to the Sun, and is heading back out of the Solar System, never to return.

Kurt and the JPO Team were very keen to capture a photograph of this 'interstellar traveller' using the Observatory's 5 inch aperture Meade Apo Refractor and also to try and obtain a spectral profile. Unfortunately, the exceptionally inclement weather here on the UK's East Coast made this impossible.

On the 16th of February, we were presented with a small 'weather window' during which, we we would have an opportunity to catch some cometary photons. As the Seestar S30 is quick to set up and as we had seen an image of the Comet captured by a local astronomer using the slightly larger Seestar S50, we decided to give it a go, more in hope than expectation to be honest.

When we looked at the one minute sub exposures that we captured and the stacked data, we could find no evidence of the comet.

Our processing technician Pip Stakkert decided to use SIRIL freeware and apply the processing python script, 'Veralux Alchemy', in order to 'stretch' any very faint  nebulosity, which might be associated with the comet's 'coma' (atmosphere). To everyone's surprise a patch of nebulosity the right size for the cometary coma and in the expected location against the night sky in the Constellation Gemini, suddenly became visible. 

We checked with the Sloan Sky Survey Database to identify any local non-cometary nebulosity, which might have been present and made visible with the Veralux script but came up with a blank. 

It is always possible to create artificial artifacts when processing very faint astronomical objects and the comet is very faint at approximately magnitude 15. We are however, relatively confident that we have actually captured an image of this rare interstellar comet before it leaves our solar system forever.

The SOHO Satellite image of C/2025 31 (ATLAS) shows water gushing from the comet. Credit: TECH STOCK and ESA

Post Perihelion the comet has shown out-gassing and dust creation. The above spectral profiles show very strong wavelengths associated with water, carbon dioxide and carbon monoxide.

Spectral Profile Credit:

Phys.org

SPHEREx imaging reveals increased sublimation activity on 3I/ATLAS

Jan 23, 2026

All very exciting stuff if 'real' ! Who would have thought that the diminutive Seestar S30 with its 30mm aperture, might capture such a tiny and dim object moving fast in the night sky? " - Joel Cairo CEO of the Jodrell Plank Observatory.

"What It Is 31/ATLAS

• 3I/ATLAS is a comet from outside our Solar System — only the third such interstellar object ever confirmed (after 1I/ʻOumuamua and 2I/Borisov). 

• Its “ATLAS” tag comes from the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey that discovered it on 1 July 2025 in Chile. 

• It has an unbound (hyperbolic) orbit, meaning it came from interstellar space and will not return after passing through our Solar System. 

☀️ Journey Through the Solar System

• Perihelion (closest approach to the Sun): reached around late October 2025 at ~1.4 AU (just inside Mars’s orbit). 

• Closest Earth approach: it passed Earth at a safe distance of about 1.8 AU (≈270 million km) in December 2025. 

• Its brightness peaked while near the inner system, but it has since faded and is now challenging to observe, requiring moderate to large telescopes if still visible. 

🔭 Scientific Interest

• As an interstellar comet, 3I/ATLAS offers a rare window into material from beyond our Solar System — potentially much older and compositionally different from typical Solar System comets. 

• Observations (e.g., spectroscopy) have been used to study its coma and tail and to better understand its physical and chemical properties" - Professor C.P T Chat visiting astro-physicist at the Jodrell Plank Observatory - the UK's most easterly Astronomical Observatory..