The oldest known to science
What Is 3I/ATLAS and Why It Matters
Scientists have determined that an interstellar object recently discovered in the solar system is a comet. The object has a clearly visible icy core and a faint tail of gas and dust, which excludes it from the category of asteroids. As an asteroid, it would have been called C/2025N1, but thanks to the robotic ATLAS observatory in Chile, it was possible to determine that the comet came from interstellar space.
So the comet was named in honor of the ATLAS system, and the letter I in its name indicates the interstellar origin of the object (interstellar). The number 3 in the name is the serial number of the object discovered in this rare category. Only two objects that came from distant stars have been noticed in the Solar System in the entire history of observations: the asteroid Oumuamua and Comet Borisov.
What Makes Interstellar Comet 3I/ATLAS Unique
There are probably more of them, but they are extremely difficult to spot: they are dim and very fast. In fact, their speed is what gives away their interstellar origin. The 2025 visitor 3I/ATLAS flies by at about 60 kilometers per second, which significantly exceeds the typical speeds of objects in the Solar System.
Mikhail Nevsky, head of the educational observatory of the Physics Department of SFedU, said that the object was probably formed in another star system and was ejected from it. This suggests that the object has been traveling through the galaxy for many billions of years, making the comet possibly the oldest of all known to science.
“We usually expect gravitational interactions or collisions to push a new comet out of the clouds of icy bodies that are at the edge of the Solar System. We have two large asteroid belts and hundreds of small clusters. But we usually don’t expect interstellar guests, and each such object is of great interest to scientists, since it brings new information from the depths of space,” explained Mikhail Nevsky.
Observation Plans with Hubble and James Webb
Scientists are already preparing an ambitious observation program: the Hubble and James Webb space telescopes will help determine the size, chemical composition, and rotation characteristics of the comet.
3I/ATLAS is currently at a distance of four astronomical units. One astronomical unit is the distance from the Earth to the Sun, or 150 million km. In October, the comet will pass at its closest distance from the Sun – 1.4 AU.
Could 3I/ATLAS Be Seen from Earth?
“And in December it will come closest to Earth, to about 3 AU, and will probably be visible to the naked eye. It will fly by, say hello, and go to other stars!” Mikhail Nevsky shared.
Meanwhile: Are Asteroids a Bigger Danger?
Before the face of Apollo
Three astronomical units sounds safe, but how often do celestial objects fly closer to Earth than to the Sun? Feel free to go higher – asteroids regularly fly so close to Earth that the distance to them is less than to the Moon.
Thus, on May 21, 2025, an asteroid from the Apollo group, “2025 KF”, 20 meters in size, flew by at a distance of approximately 115 thousand kilometers from Earth.
“The Apollo group includes those asteroids whose orbits intersect the Earth’s orbit and have a semi-axis greater than 1 AU. Those that are larger than 140 meters in diameter and fly closer than 750 thousand kilometers from our planet are considered potentially dangerous to the Earth,” explained Mikhail Nevsky.
Upcoming Near-Earth Asteroids in 2025
On September 15, 2025, an asteroid called “2024 ON” with a diameter of 220 m will fly to us. It is potentially classified as dangerous, but in reality there is nothing to worry about – it will fly by at a distance of three lunar distances. It will be difficult to even see it in a telescope, but for large telescopes it is still possible.
“Close approaches of asteroids to the Earth at a distance less than the Moon for small objects happen regularly, several times a month, and for large ones – much less often, approximately once every few years or decades,” added Mikhail Nevsky.
Humanity does not have a single plan of action in case a large asteroid is discovered heading straight for our planet, but research is underway in this direction. Many scientists are thinking about how to prevent a collision and what protocol to propose if the danger turns from theoretical to real. For now, monitoring celestial bodies is a priority.
How NASA Plans to Defend Earth From Asteroids
“Modern monitoring systems allow us to track most space objects and warn of potential threats. Even an interstellar comet, which is currently four times further than the Sun, was noticed by such a monitoring system. Currently, ground-based observatories do the main work of detecting asteroids, but they can miss objects flying from the Sun. That is why in 2027 NASA will launch the NEO Surveyor telescope into space – to detect dark asteroids invisible from Earth,” said Mikhail Nevsky.
The goal of the NEO Surveyor project is to create a systematic and comprehensive program to search for and monitor near-Earth objects, especially those in close orbits to Earth that may pose a risk of collision.
Hide the nuclear bomb
Lessons from the Tunguska Event and DART Mission
The reality of such risks became clear to humanity 117 years ago, when the Tunguska meteorite collided with the Earth on June 30, 1908. It produced an explosion with a power of 10-50 megatons – comparable to a powerful hydrogen bomb – and felled about 80 million trees over an area of more than 2,000 km².
Light anomalies were observed all over the world that day: due to the scattering of particles in the atmosphere, the nights were so bright that one could read newspapers without artificial lighting. At the same time, the meteorite did not leave a crater, which means that the asteroid’s body exploded in the air at an altitude of 5-10 km.
“And then, a hundred years ago, potential methods of counteracting meteorites emerged at the theoretical level: destroying an asteroid and removing it from orbit. The destruction method has never been tested, but to test the effectiveness of the kinetic impact method, the DART mission was carried out by a NASA space probe in 2021,” shared Mikhail Nevsky.
The DART (Double Asteroid Redirection Test) mission successfully ended with a collision with the asteroid Dimorphos on September 26, 2022. Its goal was to change the orbital period of Dimorphos around its larger companion, the asteroid Didymos. Before the impact, the period was 11 hours and 55 minutes, and after the collision with the probe, it was reduced by 32 minutes, which significantly exceeded the minimum effect of 73 seconds expected by scientists.
Why Kinetic Impact Is Better Than Nuclear Detonation
The choice of a kinetic impact probe over an explosion, such as a nuclear device for the DART mission, is driven by several key factors. First, a kinetic impact is a more predictable and safer method. An explosion, especially a nuclear one, could create uncontrolled debris that would itself pose a threat to Earth or spacecraft.
Second, the use of nuclear devices in space is limited by the 1967 Outer Space Treaty, which prohibits the placement of weapons of mass destruction in orbit. Although a nuclear explosion could theoretically be effective against large asteroids, its use requires complex legal and diplomatic agreements.
Third, most asteroids are not really rocks, but rather “rubble piles”—loose collections of rock weakly bound by gravity. A relatively weak kinetic impact could cause a blast of gas and dust, creating a jet stream that would change the asteroid’s trajectory, while a powerful nuclear explosion could scatter the debris without changing its orbit.
The DART experiment proved that kinetic impact is a viable method of deflecting asteroids, especially for objects in the 100-500 meter range, which are the most dangerous due to their abundance. A small change in an asteroid’s velocity can indeed significantly alter its trajectory, but only if the impact is made early enough.
Are We Ready for the Next One?
Potentially hazardous space objects for Earth are best detected several years before a potential collision, which explains all the resources invested in monitoring systems.
