Images of the interstellar comet 3I/Atlas, captured by the European Space Agency from Mars’ orbit, have been released. It seems that after waiting a long time for an interstellar comet, three have appeared within a decade. The most recent visitor from another star system, 3I/Atlas, was first spotted in July. As space agencies monitor this fast-moving object, here’s what we currently know.
What exactly are comets?
Comets are remnants from the formation of star systems. In our solar system, they consist of dust and ice that are about 4.6 billion years old. At the core of a comet is a solid nucleus, often called a “dirty snowball,” composed of frozen water, dust, and volatile compounds like carbon dioxide, carbon monoxide, methane, and ammonia.
As a comet approaches the sun, the heat turns its surface ice directly into gas, creating a temporary atmosphere, or coma, around the nucleus. The released dust and gas give the comet a fuzzy appearance and form tails that can extend for millions of kilometers. Comets typically have two tails: one white, made of dust that streams behind the comet, and another bluish one, consisting of charged particles or ions, which always points away from the sun.
Interstellar comets, as their name implies, originate from beyond our solar system, formed from the debris of other star systems. They can be redirected toward us by gravitational interactions with passing stars or other massive objects. So far, astronomers have identified only three such comets passing through our solar system: 1I/’Oumuamua in 2017, 2I/Borisov in 2019, and now 3I/Atlas in July of this year.
What can these interstellar comets teach us?
They provide the only opportunity for astronomers to study material from other star systems up close. When these comets pass near the sun, the dust and gases they release reveal the chemical makeup of their home systems. Michael Küppers, project scientist for the European Space Agency’s Comet Interceptor mission, Hera, explains that these objects are the first building blocks we can observe from those systems, offering insights into the conditions where they formed.
Observations of 3I/Atlas may yield more information than previous interstellar comets. While ‘Oumuamua showed little gas or dust, 3I/Atlas will come much closer to the sun than Borisov, causing it to release more material for analysis.
Is 3I/Atlas unique?
With so few interstellar comets observed, it’s hard to define what’s typical, making each one exciting. However, 3I/Atlas has some intriguing characteristics. Early estimates suggest it could be between 440 meters and 5.6 kilometers in diameter, potentially larger than ‘Oumuamua (up to 400 meters long) and Borisov (about 1 kilometer across).
An interesting feature seen in Hubble Space Telescope images is a coma that expands toward the sun, forming an “anti-tail” likely due to uneven ice sublimation on the comet. Additionally, 3I/Atlas differs from solar system comets in its chemical emissions. Observations from the Very Large Telescope in Chile indicate a high nickel-to-iron ratio in its plume, possibly from the sublimation of nickel tetracarbonyl and iron pentacarbonyl compounds.Observations indicate that light scattering from the comet is unusually polarized, which could be due to the presence of water ice and magnesium-rich silicates. But where do these comets originate?
Many comets that pass near Earth come from the Kuiper Belt, a ring of icy bodies beyond Neptune, completing their orbits around the sun in under 200 years. Others originate in the Oort cloud, a distant region extending halfway to the nearest star, where comets can take up to 30 million years for a single orbit. Billions of comets are thought to reside in the Kuiper Belt, with even more in the Oort cloud.
On June 2, 2025, David Rankin, an engineer with the Catalina Sky Survey at the University of Arizona, captured this image of Comet 3I/Atlas.
What path is the comet following?
It entered the solar system near the ecliptic, the plane of Earth’s orbit around the sun, which is also where other planets orbit. There’s no risk of it colliding with Earth or any other planet; its closest approach to Earth will be 240 million kilometers, over 1.5 times the distance from Earth to the sun.
Avi Loeb, a U.S. astronomer who previously suggested ‘Oumuamua might be alien technology, has also speculated that Comet 3I/Atlas could be artificial. He points to its trajectory passing near Jupiter, Mars, and Venus as possibly planned, and notes its origin aligns closely with the 1977 Wow! Signal, considered by some as a potential alien transmission. However, Loeb acknowledges that it’s far more likely a natural interstellar object.
Küeppers agrees, stating, “It looks and acts like a comet, so there’s no reason to think otherwise. If you analyze its path and various angles, you’ll always find something statistically unlikely.”
What’s next for observations?
Astronomers plan to capture more images using ground and space telescopes, Mars orbiters and rovers, and probes like the European Space Agency’s Juice mission. Recently, ESA released images from two Mars missions, the Trace Gas Orbiter and Mars Express, showing the comet as a small dot with a visible coma as it passed 30 million kilometers from Mars, indicating it’s becoming active due to solar heat and radiation. Although the comet will be behind the sun at its closest approach to Earth, it will reappear in late November, offering another opportunity for study.
Frequently Asked Questions
Of course Here is a list of helpful FAQs about the observation of a rare interstellar comet
BeginnerLevel Questions
1 What is an interstellar comet
An interstellar comet is a comet that originates from outside our solar system Unlike comets from our own Oort Cloud these visitors are just passing through on a oneway trip
2 How do we know its from outside our solar system
Scientists determine this by calculating its path or orbit If its speed and trajectory are too fast and not a closed loop around the Sun it must have come from interstellar space
3 Whats so special about studying a comet from another star
Its like a cosmic messenger It carries material that was formed around another star giving us a direct sample of the building blocks of a different planetary system
4 Can we see this comet with the naked eye
Most interstellar visitors are extremely faint and require powerful telescopes to be seen Its very unlikely you could see it without professional equipment
5 Is this comet dangerous Could it hit Earth
No these comets are not a threat They are detected when they are very far away and their trajectories are carefully tracked showing they will pass by safely
Advanced InsightFocused Questions
6 What specific insights can its composition provide
By analyzing the gases and dust it releases we can learn what chemicals minerals and ices are common in other star systems This tells us if the ingredients for life are universal
7 How does it compare to comets in our solar system
This is a key question By comparing its composition size and behavior to local comets like Halleys Comet we can understand if our solar system is typical or unique in the universe
8 What can its structure tell us about its home system
The comets physical structurewhether its a single object or a loose pile of rubblecan reveal the physical conditions and formation processes in its original planetary system
9 What technology are we using to study it
Scientists use the worlds most powerful groundbased and space telescopes to perform spectroscopy which breaks down its light to identify its chemical fingerprint
10 What is the biggest challenge in observing it
The main challenge is that these objects are usually small faint and moving
