Comet C/2025 K1 (ATLAS) passing by Earth and shedding mass in front of the Great Bear's nose.

 

The Comet C/2025 K1 (ATLAS)
captured with the JPO's Seestar S30 robotic SMART telescope in EQ mode.
A cropped stack of 3x60sec subs. Image credit: Kurt Thrust.

" Wonders never cease, here in Lowestoft, we had a one night window of clear weather and no moonlight on the 23rd of November. Sadly, our Director Kurt is getting on a bit and is currently, what is known in the medical trade, as 'a bit Uncle Dick', so, even with the encouragement and support of the JPO Team I decided against an early morning run of the 5 inch refractor to capture the double Jovian Moon shadow transits. We did however use the quick an easy to set up Seestar smart telescope to capture the comet which has fallen apart since its encounter with the Sun. We have no financial connection with ZWO the Seestar's manufacturer nor with the telescope's supplier First Light Optics, but we would recommend both in good faith.⭐⭐⭐⭐⭐ 

The Seestar S30 is a great purchase for either a beginner or an expert stargazer and would make a great Christmas gift. It comes with excellent software, which is regularly updated and costs currently well under £400. If you want all the add ons to enable long EQ mode imaging sessions (not essential but a bonus) you would still have change from £500. The Seestar's only real downside is its use for imaging the planets, literally its short focal length and small aperture lens system are inappropriate for detailed images of Saturn, Jupiter and Mars. It does capture nice Lunar disc images and comes with a white light filter for capturing the Sun's photosphere with sunspots as available. What the Seestar really excels at is images of large and bright galaxies, star clusters and nebulae, of which there are many in the night sky. In our opinion it is also excellent for finding and capturing even faint comets. Other great features of the Seestar S30, are its easy use via a smartphone or tablet,its fast deployment in the field and its large software based library of interesting astro-objects, which it will 'GOTO' at the press of a button.  It makes for a great travel scope and is easy to transport on a plane as hand luggage. Best of all, on a very cold night, Kurt can control the Seestar remotely from the warmth of the Jodrell Plank Observatory Visitor Centre Lounge." - Joel Cairo CEO of the JPO.

"Comet C/2025 K1 (ATLAS) presents a textbook and visually dramatic example of a dynamically new Oort-cloud visitor reacting to a first close passage by the Sun. Discovered by the ATLAS survey on 24 May 2025, the object showed the rapid brightening characteristic of a fresh, volatile-rich nucleus as it plunged sunward from deep space.

Physically, the comet’s behavior around perihelion is governed by two simple processes taken to extremes: solar heating of near-surface ices and the differential gravitational stresses that act on a loosely consolidated nucleus. As the comet approached perihelion (closest approach to the Sun, reached on 8 October 2025 at roughly 0.33–0.334 astronomical units), sunlight drove intense sublimation of water, CO and other ices. The resulting gas outflow inflated a bright coma and produced the familiar ion and dust tails; at the same time the outgassing torque, thermal gradients, and small tidal stresses created fractures in a weakly bound nucleus. Observers reported erratic brightness changes and morphological distortion in the days and weeks around perihelion — signatures consistent with internal weakening and fragmentation under solar heating. 

Following that close solar encounter, high-resolution and amateur images recorded that C/2025 K1 had broken into multiple pieces (commonly labeled A, B, C in the observing reports). The fragmentation is important because it fundamentally changes the comet’s subsequent evolution: separate fragments present more surface area to sunlight and lose mass faster, and they spread along slightly different orbits so the single nucleus becomes a family of fading bodies. Multiple professional write-ups and image sequences document this breakup and the rapid dispersal of material in the coma and tail. 

The JPO's Seestar  smart telescope has insufficient resolving power to show the individual parts of the original comet nucleus but even a cursory inspection of our image shows that the nucleus has been smeared out and made more granular after its brief and first close encounter with the Sun.

From an orbital perspective the comet is a “dynamically new” Oort-cloud object on a long-period inbound trajectory; modest changes to the orbit caused by non-gravitational forces (outgassing) and the fragmentation event mean that the precise future paths of individual fragments are uncertain. Published ephemerides show perihelion at ≈0.334 AU and predict that fragments will make their closest approach to Earth later in 2025 (around 24–25 November) at a distance on the order of 0.40 AU — close enough for well-equipped backyard telescopes and for continued photometric and spectroscopic monitoring but far from any hazard. Depending on the precise post-perihelion velocities imparted to fragments, some pieces can remain bound to the Sun on very long elliptical orbits while others may receive enough change in orbital energy to be placed on weakly hyperbolic (slightly >1.0 eccentricity) outbound trajectories; published solutions for different fragment solutions already show small variations in eccentricity consistent with that uncertainty. 

Dynamically, continued astrometric tracking of the fragments over weeks to months is the only practical way to determine whether any piece remains on a long bound orbit or whether the body (or some fragments) will depart the solar system on an effectively hyperbolic path. Current orbit solutions already reflect slight outbound eccentricities for some fragment solutions, but the final verdict depends on more data and on correctly modeling non-gravitational accelerations from outgassing.

In short: C/2025 K1 (ATLAS) taught astronomers something immediate about the fragility of fresh Oort-cloud nuclei when exposed to strong solar heating — it brightened, stressed, and then partially disintegrated during perihelion — and it will continue to be scientifically valuable as the fragments evolve. Continued imaging, spectroscopy and precise astrometry through its November Earth-pass will let observers quantify mass loss, grain composition (which already hints at an unusual spectral character in some reports), and the post-breakup orbital fate of the fragments. For the public, the object’s remnants should remain an accessible and instructive target for telescopes this autumn; for researchers, the event is a rich real-time laboratory for cometary physics". - Professor G.P.T Chat visiting astrophysicist at the JPO.