A new comet has been discovered in the Main Asteroid Belt.

In the Main Asteroid Belt between Mars and Jupiter, unusual objects have been observed that exhibit characteristics of both asteroids and comets. These are referred to as active asteroids. Recently, one such celestial body was discovered. Initially, it was identified as a typical asteroid, but it has since been observed twice displaying a distinct comet-like tail.

https://naked-science.ru/article/astronomy/v-glavnom-poyase-asteroid2024-12-05 10:01:04

The main asteroid belt is considered by astronomers to be an unsuitable place for comets: it is not far enough from the Sun for sufficient ice to have remained over the 4.6 billion years of the Solar System's existence. To recap, this belt is located between Mars and Jupiter and contains millions of celestial bodies. In the past, there were speculations that it was made up of fragments from a planet that once existed — the hypothetical Phaeton. Today, astronomers note that a planet could not even form there, as it was and continues to be hindered by Jupiter's gravity.

Comets most often come to us from more distant locations. One of these is the Kuiper Belt, located beyond Neptune, and another is the so-called Oort Cloud: a hypothesized sphere with a radius of a whole light year, where countless mainly icy bodies are distributed. When such a body approaches the Sun, volatile substances begin to evaporate from its surface, which we observe as the comet's tail.

Since the "homeland" of almost all known comets is somewhere on the outskirts of the Solar System, their orbits are extremely elongated: their ellipses stretch from the vicinity of the closest planets to the Sun to Neptune and Pluto or even further. This is one of the typical characteristics of comets. Asteroids, on the other hand, usually have more or less circular orbits.

However, as has been discovered in recent years, there are interesting exceptions to this general rule: an increasing number of objects with asteroid-like orbits and comet-like behavior are being found in the Main Belt — they emit tails. However, this is not always considered a result of ice sublimation and other materials that easily vaporize when heated. For instance, a "tail" can sometimes form after a celestial body collides with another object.

All such "hybrids" are classified into the category of so-called active asteroids. There are several dozen of them, and now another one has appeared on this list — 456P/PANSTARRS. It has actually been observed since 2021, but recently a team of astronomers from the U.S. reported in their article for Research Notes of the AAS that it is nothing less than a Main Belt comet.

Scientists explained that they have seen the tail of this object twice, both times during its approach to the Sun. The orbit of 456P/PANSTARRS is slightly elongated, but it does not stretch across the entire Solar System like typical comets; instead, it remains within the asteroid belt. Its perihelion (the closest point to the Sun) is about 2.8 astronomical units away, while its aphelion (the farthest point) is at 3.5 astronomical units.

Recall that an astronomical unit is the distance from the Earth to the Sun, approximately 150 million kilometers. Mars is, on average, one and a half astronomical units from the Sun, and Jupiter is about five astronomical units away.

456P/PANSTARRS completes a full orbit around our star in just over five and a half years. Its size (or rather, its "nucleus," meaning the main part) is about one kilometer.

Recently, in October 2024, the object passed through perihelion, and it was then that it was observed as a comet twice. The fact that it emitted a tail during this time indicates that its material is vaporizing under the influence of the Sun. According to astronomers, it must contain a significant amount of ice, which allows it to be classified as a comet rather than an asteroid that merely "pretends" to be a comet.