Introduction to comet Atlas; Foreign visitor of the solar system!

The interstellar comet C/2025 K1, known as “Atlas”, has attracted the attention of the scientific community and astronomy enthusiasts since mid-2025.

Unlike the usual comets that are born in our Solar System, this comet came from interstellar space, making it the third confirmed interstellar object to visit the Solar System, following 2017’s 1I/’Oumuamua and 2I/Borisov. Its discovery and subsequent observations will change the way astronomers think about the composition and behavior of comets beyond the solar system.

Discover the Atlas

Comet Atlas was first identified by the “Asteroid Terrestrial-impact Last Alert System” or “ATLAS” and known as C/2025 K1. It is a network of wide-field telescopes designed to detect small objects with a chance of hitting Earth.

The movement of comet Atlas in the background of stars and its discovery
Credit: ATLAS/University of Hawaii/NASA

First, the Atlas station in Chile detected this object on July 1 and 2, 2025 (10 and 11 July 1404), and subsequent observations very quickly showed that its orbit is hyperbolic; A clear sign that it is not in the gravitational fence of the Sun and came from interstellar space, and for that reason it was named “Third Interstellar/Atlas” (3I/ATLAS). Rapid data sharing between observatories around the world allowed orbital surveys and physical tracking to begin within days.

The importance of the interstellar guest Atlas

“Comet” is a space body that consists of dust, frozen gas, rock and organic matter, and when it gets close to the sun, its ice evaporates, creating a bright and beautiful tail in the opposite direction of the sun’s rays. This tail and central core are the main characteristics of comets.

But most comets orbit the Sun in elliptical orbits, which makes them stay in the Solar System. In contrast, interstellar objects come from other star systems and travel along elongated hyperbolic paths. Thus, they provide valuable natural samples of materials and conditions in other parts of the galaxy.

Comet Atlas’ orbit in the solar system
Credit: JPL/Bolin, et al.

But it should be kept in mind that these objects have never been proven to be alien spaceships that have traveled to us from the depths of the universe, and these controversies around them remain only at the level of hypothesis and even pseudoscience. They can be considered as small bodies that carry the chemical and physical history of other planetary systems with them. Indeed, any interstellar visitor offers a unique opportunity to test models of planet formation, volatile chemistry, and the distribution of organic matter throughout the Milky Way.

The source of Atlas

Although scientists can determine the exact direction of the Atlas comet’s entry into the solar system, this does not determine in which part of the galaxy it originated. These estimates are not as simple as tracing a straight line because if the mass has traveled through space for millions of years, its path has been altered many times by the gravity of stars, molecular clouds, and even the spiral arms of the galaxy itself.

But it can be seen that it probably started moving in an orbit around a star. According to researchers, Atlas may have been ejected from its parent star system due to a close encounter with a giant planet or another nearby star. According to the observations of the James Webb and “SPHEREx” space telescopes, this comet has a lot of carbon dioxide, which indicates that it was formed at a distance from its mother star; That is, where the temperature is cold enough for carbon dioxide to turn into a solid.

Preliminary studies also suggest that Atlas could be between 3 and more than 13 billion years old, meaning it could even be older than the 4.6 billion year old Solar System. On the other hand, if this estimate is correct, it would make it the oldest comet ever seen.

Features of the Atlas comet

One of the efforts of the researchers has been to investigate the characteristics of comet Atlas in order to have a complete view of it as the third confirmed interstellar object.

Comet Atlas Velocity

As it approaches the Sun, Comet Atlas accelerates due to the Sun’s gravitational pull. This velocity reaches its maximum value at perihelion, where the comet is expected to be traveling at 68 km/s relative to the Sun.

Dimensions and composition of Comet Atlas

Estimates of the size of the nucleus of Comet Atlas vary. Preliminary investigations showed that the core, depending on the assumptions related to reflection (albedo) and dust production, has a diameter of several hundred meters to several kilometers. In relation to the composition of the constituents, spectroscopic measurements reveal a rich chemical composition.

Comet Atlas from the Jumnai Observatory
Credit: Gemini Observatory/NOIRLab/NSF/AURA/Shadow

In particular, the high ratio of carbonaceous volatiles (such as carbon dioxide) to water compared to many solar system comets is noteworthy. This chemical fingerprint points to different formation environments, or thermal histories, in the comet’s parent system, and is a kind of direct evidence that astronomers use to refine theories about how solids and ices form and evolve around other stars.

Severe water loss

One of the most newsworthy findings about Comet Atlas came from its ultraviolet and X-ray observations, which showed that while it was still far from the Sun, the object was ejecting unexpectedly large amounts of water vapor, stretching up to about 2.9 AU. Instruments including NASA’s SWIFT observatory have measured water loss rates of tens of kilograms per second, a rate researchers liken to a “fire hose” and unusual for comets in the Solar System at that distance.

These observations have raised new questions about how the ices of interstellar comets form and have led scientists to ask whether comets that form around other stars can behave very differently from our familiar comets.

What is seen in the telescope

Comet Atlas has been observed by a wide range of instruments, including ground-based telescopes such as Jumnai and other large observatories, space telescopes such as Hubble, Mars orbiters that were properly oriented during the comet’s passage, and, of course, amateur astronomers’ telescopes.

Comet Atlas from Hubble’s view
Credit: NASA, ESA, D. Jewitt (UCLA), J. DePasquale (STScI)

Hubble images showed a teardrop-shaped halo of dust erupting from a compact core, while Mars orbiters captured more detailed views as the comet passed close to the Red Planet, helping scientists monitor the comet’s activity at different distances and angles. The European Space Agency’s “ExoMars” and “Mars Express” orbiters also pointed towards the comet as it approached Mars to quickly explore this interplanetary asset.

The method of observation

The position of the Atlas comet in the sky is not expected to be a pleasing sight to the naked eye. According to the modeling of the comet’s brightness and geometry, this mass will remain dim, and you will need to use astronomical instruments, especially a telescope, to observe it. As a guide to where to look, websites like TheSkyLive and other similar astronomical tools provide up-to-date location, magnitude predictions, and sunrise and sunset times to observers using telescopes and binoculars.

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The closest distance of this comet to Earth in 2025 is predicted to occur on November 25, 2025 (December 4, 1404) and reach approximately 0.403 AU (about 60 million km). A distance that is still far for night sky watchers, and therefore expected to be invisible even then to the naked eye, requiring at least moderate amateur telescopes. For better observation, observation sessions should be planned around sunrise or sunset when the comet’s angular distance from the sun is in a favorable position.

The appearance of comet Atlas during a lunar eclipse
Credit: Michael Jäger/Gerald Rhemann

Messenger of the interstellar world

Each interstellar comet raises more questions than it answers. For example, to what extent is the composition of Atlas representative of other star systems, and did it form in a very different region than our Kuiper Belt or Oort Cloud? Continuous monitoring of its motion and laboratory analysis, modeling and comparison with similar objects will provide a better classification of Atlas’ position.

Comet Atlas is also a rare interstellar messenger that has surprised astronomers by showing the volatile behavior of substances and its distinctive chemical characteristics and attracted the attention of amateur astronomers and astrophotographers to raise their instruments to the sky and not miss the opportunity to meet this interstellar guest.

Although this comet will not be visible to the naked eye, the collaboration to discover, identify its behavior and image it demonstrates the power of international joint scientific efforts, especially when a guest from beyond the solar system arrives close to home. It remains to be seen how far we can understand its message.

Cover photo: A graphic design of Comet Atlas
Credit: Robert Lea

Sources: NASA, Space, Planetary Society, Live Science