Interstellar comet 3I/ATLAS is approaching Earth. What you need to know

On December 19, Comet 3I/ATLAS, the third known interstellar object to become a "guest" in the Solar System, will approach Earth at a distance of 270 million km. Astronomers are putting forward theories about the composition of a space object, its size, and its links to aliens. Izvestia figured out where the truth was and where the fiction was.

What is known about the comet

• Comet 3I/ATLAS was discovered on July 1, 2025 by the ATLAS telescope in Chile (funded by NASA). At that time, it was located at a distance of about 670 million km from the Sun, within the orbit of Jupiter. In early October, the comet approached Mars at a distance of 29 million km, and at the end of the same month — to the Sun (203 million km). After that, it began to move rapidly away from the center of the Solar system.

• Researchers believe that 3I/ATLAS may be the oldest comet ever discovered. Its age probably exceeds 7 billion years, that is, it is 3 billion years older than the Solar system.

• The trajectory of 3I/ATLAS indicates its origin in the part of the Milky Way called the "Thick Disk". This is a layer of ancient stars that are located above and below the Thin Disk where the Sun and most of the stars of the galaxy are located.

• At the time of detection, the comet was moving at a speed of 221 thousand km/h. As it approached the Sun, its speed increased, and at the point of maximum convergence — perihelion — increased to 246 thousand km/h. This is the highest speed ever recorded by a "guest" of the Solar System.

The comet's core consists of ice, surrounded by a cloud of gas and dust called a coma. The coma and the nucleus form the "head" of the comet. According to scientists, the diameter of the core of 3I/ATLAS ranges from 440 m to 5.6 km.

Alien Comet: Why everyone is watching 3I/ATLAS and is it dangerous

Researchers believe that it may be almost twice as old as the solar system.

New observations show that the comet may be covered with erupting cryovolcanoes, which are also called ice volcanoes. They became more active as the comet approached the Sun. Scientists believe that the comet has a lot in common with trans-Neptunian objects, such as Pluto.

• Judging by the photos taken in November, the comet may have two tails: a "plasma tail" consisting of electrically charged gas, and a "dust tail" made of tiny solid particles.

• As 3I/ATLAS approached the Sun, it lost more and more of its mass as the frozen gases turned into steam. When heated, carbon dioxide, carbon monoxide, and carbonyl sulfide were also released. Moreover, the comet produces an extraordinary amount of carbon dioxide — more than the comets of the Solar system. Scientists have also noticed that 3I/ATLAS emits carbon-rich chemical compounds much more actively than any other known comet. One such compound is methanol, which has not been detected in other interstellar objects. Another difference from the comets of the Solar System is that there is a lot of red in the structure of the 3I/ATLAS spectrum, which may indicate an unusual chemical composition. At the same time, the latest images of the comet showed that after approaching the Sun, it became brighter and acquired a green hue, which indicates an increase in the activity of the object.

• In addition, 3I/ATLAS became the first interstellar comet to be photographed in X-ray light. An image taken in December from the XMM-Newton spacecraft shows a bright red spot that looks like a fiery beacon. X-rays occur when gas molecules emanating from an object collide with the solar wind. Thanks to these data, scientists can find out what the comet is made of. Nitrogen, oxygen, and carbon have already been detected in the area near the core.

Does the comet pose a danger to Earth

• Astronomers have classified 3I/ATLAS as an interstellar object due to the hyperbolic shape of its orbit - the comet does not move around the Sun. It does not pose a threat to the Earth: the comet will approach our planet at a maximum distance of 270 million km (this is about 1.8 times more than the average distance from the Earth to the Sun). It will happen on December 19th.

• 3I/ATLAS is expected to be visible with an amateur telescope in late 2025 and early 2026. The best time for this is before dawn.

• In March, the comet will approach Jupiter, passing from it at a distance of 53 million km. 3I/ATLAS is likely to cross Neptune's orbit in 2028. Eventually, the comet will pass through the Solar System and continue its journey through interstellar space.

Could 3I/ATLAS be related to aliens

• After the discovery of asteroid 1I/Oumuamua, some experts suggested that it was a disguised spacecraft due to its features. As 3I/ATLAS was being studied, similar hypotheses began to emerge regarding the comet. Astrophysicists point to a number of "anomalies" that allegedly cast doubt on the fact that 3I/ATLAS is a comet. For example, it was noticed that the object changed course slightly after passing perihelion. In addition, 3I/ATLAS had an anti-tail (pointing towards the Sun, not the other way around, as usual) and an unusual light pulsation. One of the most notorious scientists who consider 3I/ATLAS to be a controlled alien object is Avi Loeb, an astrophysicist and professor at Harvard University. In particular, he warned that when approaching Jupiter from 3I/ATLAS, some devices may be launched to collect data in the interests of an extraterrestrial civilization.

Such theories often attract laypeople, but they are always met with a barrage of well-founded criticism. And in the case of 3I/ATLAS, everything is exactly the same — other experts have found quite scientific explanations for all the detected "anomalies". Scientists are inclined to believe that 3I/ATLAS behaves like an ordinary comet.