In July 2025, the Atlas system detected a new body whose orbit was so hyperbolic that it was not doubtful on its nature outside the solar system. It was immediately baptized 3i/Atlas, as the third interstellar object identified after 1i/ʻoumuamua and 2i/Borisov.
According to its trajectory, Its entry speed was estimated at almost 60 km/s with a retrograde inclination, This is the fastest interstellar ever recorded and, thanks to this, it will reach its perihelia on October 29, 2025 to 1.35 astronomical unit of the sun.
The scientific community is impatiently awaiting the opportunity to observe how this traveler reacts to solar heat, because it will be the first time, since his formation around a distant star, which he will be confronted with intense warm -up after having wandered during millennia in the cold of the interstellar space.
A few days ago, The Hubble space telescope pointed out its instruments to capture the first high -resolution images and revealed an active object, Surrounded by ejected dust hair mainly towards the sun and a thin tail oriented in opposite direction.
This early activity, detected at more than 3.8 astronomical units, already suggests that its surface is covered with ice capable of sublimating long before reaching the maximum heat of its perihelion, so that it could cross this point without any particular brilliance.
A core hidden behind the dust
The images of the venerable telescope did not directly show the nucleus, because the light that we perceive comes almost entirely from dust in the hair, which makes its estimate of difficult size. The calculations fix a maximum limit of 2.8 kilometers of radius, although it can be much smaller.
This result would place him in a scale comparable to 2i/Borisov and well above 1i/ʻoumuamua, the size of which did not reach 100 meters. Here, the key lies in the enormous production of dust which hides the nucleus as a brilliant cover.
Hubble also revealed that the program is not symmetrical, because a range of material projects towards the sun, Probably due to a sublimation located on the diurnal side. The low antisolaire tail, produced by the radiation pressure, suggests that the expelled particles are relatively large.
It has been observed that the particles are ejected towards the sun at a higher speed (about 22 m/s) than those which move laterally compared to its orbit. This confirms the idea that a more powerful particle jet exists in a particular area of the surface.
How to lose mass without strict diet
The team estimated that the visitor loses between 6 and 60 kilograms of dust per second, Depending on the average size of the particles, which could vary between 1 and 100 micrometers, a comparable, even higher value, that of 2i/Borisov.
If the gas which propels the dust is water vapor, CO2 or CO, it would suffice from frozen areas covering a few tenths of square kilometer to support the observed activity, which suggests a small but very effective nucleus in the release of matter.
Its high entry speed implies that he wandered for billions of years through the galaxy and, During this time, the cosmic radiation shaped him a surface layer of dark organic matter protecting the underlying ice.
In addition, the fact that the activity focuses on the enlightened face could mean that this “crust” is thin, perhaps only a few centimeters, or that the axis of rotation is oriented to maintain the same area exposed to light during its approach.
Interstellar travelers
3i/Atlas observations make it possible to compare the three known interstellar objects, Because while ʻoumuamua seemed rocky and without hair, and Borisov presented a classic comic behavior, 3i combines a probably small nucleus with a very intense activity.
The predominance of dust on the nucleus light makes it difficult to know its form, its rotation and its exact composition, in addition to complicating the estimate of the number of similar objects which could cross the solar system without being detected.
If its shine is largely due to the hair, Many other inactive nuclei – smaller or without active sublimation – could go unnoticed for our telescopes, and their detection will require more sensitive instrumentation or targeted research.
In the coming months, as it approaches the sun, 3i/Atlas will offer a unique opportunity to study the way in which an interstellar comet reacts to heat and each data collected will be an open window on other planetary systems.