From speculation about alien ships to theories about time travellers, i3/ATLAS has generated unprecedented collective excitement. I find this widespread enthusiasm particularly engaging. Having grown up watching Carl Sagan sharing his ufological theories in Cosmos. Now I have the pleasure of experiencing this anomaly and, overall, listening to the curious scientific explanations that are emerging.
In these times when misinformation is everywhere, I will be gathering and updating the different peculiarities of this stellar body, always in favour of objectivity and thus avoiding the sensationalism and opportunism I see in some other media channels.
The goal is that we all have enough information to form a critical opinion so we can enjoy this phenomenon together, regardless of the wild theory that might be living in our heads ;)
👾Anomalies
Its path follows Newton’s equations: a hyperbolic trajectory. But unlike other well-described comets we know (Halley, Encke…), this shape is open. It is neither an ellipse nor a circle; it is a Hyperbola. That means the Sun cannot capture it because its speed is too high. Its inertia beats the Sun’s gravity, so it escapes forever.
This tells us something important: it does not belong to our Solar System. It comes from outside, from another star system. That alone makes it extremely interesting, because only three such objects are known: 1I/‘Oumuamua, 2I/Borisov, and itself: 3I/ATLAS.
2) Large size
Like any active comet, it has a solid icy nucleus. As it approaches the Sun, the ice sublimates, forming a gas-and-dust coma.
The coma makes it hard to measure its size, but early estimates suggested ~20 km. Newer observations place it between 300 m and 5 km. For putting it in comparison, it is 5 times the size of 2I/Borisov or 25 times larger than Oumuamua
3) Galactic-centre procendence
Its incoming direction points from the constellation Sagittarius, close to the galactic plane, a region rich in stars. This hints at a possible origin deep in the Milky Way. (There was also mention of a 9% difference with the “Wow!” signal, but the context is unclear.)
4) Extremely high Speed
Around 200,000 km/h, making it the fastest comet ever observed from Earth.
5) Older than the Solar System
And also the oldest object ever seen in the Solar System. It could be as old as 11 billion years, or even more.
For context:
The Universe is about 13 billion years old
The Solar System is about 4 billion years old.
Anything we see within it is at most that age.
So we are talking about an object formed at the dawn of the cosmos, long before we appeared in the Universe. This already gives hints at how strange it might be.
6) Strange trajectory
Its passage through the Solar System is also peculiar because, unlike the other two extragalactic visitors, 3i/ATLAS travels within the plane of the Solar System, also known as the ecliptic, the same plane in which all planets and the Sun lie.
Besides being a great coincidence, it is great luck, because it gives many opportunities to observe and measure it carefully. This is not only because we have more time, but also because it passes close to planets and therefore close to our telescopes spread across the system.
7) Confusing composition
When the composition of this object is analysed, something truly strange appears. It contains only 4% water vapour by mass, and its CO₂ content is much higher than usual, at almost 32%.
A 1:8 CO₂–water ratio like this has been observed only once in the history of Solar System comets. It is highly abnormal and arouses tons of sci-fi theories.
The gas plume above 3I/ATLAS contains much more nickel than iron; a spaceship? I don’t think so, but it is definitely something extremely unusual.
9. Negative polarisation
Negative polarisation was measured before perihelion, a phenomenon not observed in other known comets, including 2I/Borisov.
It is a very narrow and extremely deep curve, as stated by the authors themselves in the paper “Extreme Negative Polarisation of New Interstellar Comet 3I/ATLAS“, written by a large international collaboration.
They openly recognise that they are facing something totally new, never seen before. They suggest it must be a new type of comet, something completely rare and strange compared to what is known so far, almost more similar to a small planet than a comet.
10. Tail behaviour
Usually, a comet has a tail, nothing surprising at all. This is due to the Sun’s rays acting on the comet. It is well known that heat causes ice to sublime, leaving behind a trail of gas and dust.
Well, with ATLAS, something abnormal happened. During July and August, the tail pointed in the opposite direction from usual. Instead of pointing away from the Sun, it pointed toward the Sun, and only later changed and formed the characteristic comet tail we all imagine.
11. Pulses?
There have been some peculiar articles, news posts, and online comments suggesting that ATLAS emits a signal that could be a message to its original planet, as if it’s contacting “home”.
This sounds strange, and in fact, after looking for the original source, nothing has been found. I have no confirmation of this wild feature.
12. Brightness increase
The latest images of 3I/ATLAS, taken before it was hidden by the Sun, show a rapid and remarkable increase in brightness. This was published in a scientific article titled “Rapid Brightening of 3I/ATLAS Before Perihelion”, by scientists at the Lowell Observatory in Arizona, using several instruments: STEREO, SOHO, and GOES, following 3I/ATLAS during September and October. They observed that the brightness intensity had changed by a factor of 5 compared to its value at the beginning of the month.
13. Colour change
Apparently, the object has changed its brightness colour from reddish to greenish, and finally to bluish.
The reddish tone can be attributed to dust scattering.
The greenish stage can be explained by the emission of specific gases.
But the reason why it has now turned blue is not understood at all.
It is a great mystery. This colour might be explained by light refraction or by the object’s temperature. Colours toward the blue imply higher temperatures.
14. Non-gravitational acceleration
There is a possible natural explanation based on Newton’s third law: it might be expelling gases. If sublimation releases gases with a rocket-like effect, the object could accelerate.
How much would it need to lose? We can calculate the mass it would have to shed to produce that acceleration. The estimate is about 5.5 trillion tons lost after passing the Sun. This is a lot, around 15% of its initial mass, something that should be detectable.
Last review: 28/11/2025
