Astronomers have discovered seven asteroids that exhibit behavior similar to that of tailless comets.

Comets are distinguished from asteroids by their abundance of ice and other volatile substances, which can be observed around the celestial body in the form of a coma—a small "atmosphere." However, there are instances when no coma, and certainly no tail, is present. Nevertheless, it appears that material can sometimes be ejected from what seems to be a solid body. These unusual occurrences are classified as a special category of celestial objects known as "dark comets." While it's challenging to determine their exact number, scientists recently discovered seven more and even mapped their distribution throughout the Solar System.

2024-12-12 10:01:40https://naked-science.ru/article/astronomy/astronomy-nashi-sem-aster

Dark comets are a newly identified class of celestial bodies in the Solar System, introduced after a series of puzzling observations in recent years. The story began in 2016 when astronomers noticed an ordinary near-Earth asteroid named 2003 RM.

This asteroid primarily orbits between Mars and Jupiter but regularly comes close—by cosmic standards—to Earth's orbit. Since its discovery in 2003, this asteroid has been observed hundreds of times, its orbit thoroughly studied, yet no coma or tail was ever detected. Suddenly, in 2016, it was found that the asteroid had unexpectedly deviated from its predicted trajectory—gaining unanticipated acceleration.

There was no convincing evidence to support the possibility of it colliding with another body; the asteroid accelerated in a "sparsely populated" region. There is also the so-called Yarkovsky effect—an extremely weak thrust generated by thermal radiation from the surface of a celestial body under the influence of the Sun, but the acceleration of 2003 RM was too significant for such an explanation. Thus, only one option remained—reactive thrust from a sudden gas outburst. This suggests that the asteroid exhibited cometary activity.

Interestingly, a similar situation occurred with the well-known interstellar object Oumuamua in 2017: it appeared as a long stone slab with no signs of surrounding gas or dust, yet it also unexpectedly ended up much farther from us than astronomers had calculated during its departure.

Subsequently, six new cases of this kind were observed in the Solar System, and recently a team of astrophysicists from the USA, Italy, and Germany reported seven more. In total, there are 14 so-called dark comets (Oumuamua is not included, as it does not belong to the Solar System).

In an article for the journal Proceedings of the National Academy of Sciences, scientists explained that their new observations allow for the differentiation of two populations of such objects: "outer," larger dark comets on relatively elongated orbits, and "inner" ones, located no farther than Mars, which are much smaller and have very rounded orbits.

The researchers emphasized that "asteroids that wish to be comets" are intriguing in the context of questions regarding the origin of life on Earth: these celestial bodies may have delivered the necessary substances to our planet.

Previously, astronomers proposed the hypothesis that dark comets were once genuine, fully-fledged comets that eventually disintegrated and "dried up," yet some amount of volatile substances still remains within them and occasionally reveals itself.