The announced end of a comet that grazes the Sun

It is thanks to the space solar observatory SoHO (Solar and Heliospheric Observatory) that the comet 323P/SOHO was first observed in 1999. Originally designed to study various solar processes and features, the satellite SoHOplaced in orbit around our Star, has also allowed the identification of more than 4,000 comets due to its excellent observation point. The almost majority of comets thus detected belong to the class of grazing comets — comets with a perihelion extremely close to the Sun ; because of this proximity, these objects are difficult to observe, so the number of grazing comets detected is much lower than predicted by the digital models.

A comet that behaves strangely

With a period orbital a little over 4 years old, comet 323P/SOHO has a highly eccentric orbit: its distance from the Sun varies from 5.1 AU to its aphelion (point of the orbit furthest from the Sun) only 0.04 AU at its perihelion (point closest to the Sun). An international team ofastronomers made the first ground observations of the comet (it thus becomes the second comet, detected by SoHO, observed by non-solar observatories), and points out the singular nature of its behavior.

During its approach to its perihelion point during the year 2020, the observations of 323P/SOHO, carried out with the telescope Subaru (based in Hawaii), showed no cometary activity. On the other hand, after passing its perihelion point on January 17, 2021, astronomers were able to detect astonishing characteristics: the comet would have developed a long tail, probably composed of cometary debris. The researchers also succeeded in identifying the presence of two fragments with a diameter of about twenty meters each, coming from 323P/SOHO, allowing them in passing to estimate a loss of mass of the comet can approach 10%: the comet seems to gradually destroy itself over its successive passages near the Sun.

But another feature intrigues scientists: using digital models using photometric data from the comet, the team of astronomers was able to estimate the rotation period of its nucleus – part solid of a comet, with a diameter of about 172 meters in the case of 323P/SOHO — at just over half an hour, one of the fastest rotations known of any comet in the Solar system. According to the researchers, this rapid rotation is a sign of strong cohesion within the nucleus, making it potentially more resistant to gravitational forces exerted by the Sun.

A near end of life?

According to their observations, this comet would be part of the family of Jovian comets — comets whose periods of revolution would be between the period of revolution of Jupiter and half of it. Only, ordinarily, these comets, containing significant quantities of volatile elements, are generally recognizable by the tail formed behind them when they are heated by the Sun. In view of the nature of the tail developed by 323P/SOHO, scientists agree that it would have, on the contrary, been formed under the action of its rotational instability and the significant gradient temperature within the nucleus as it approaches the perihelion point.

Thus comet 323P/SOHO could survive its successive passes near the Sun thanks to the cohesion of its nucleus, but not indefinitely: in addition to its rotational instability, the comet is in orbital resonance with Saturngradually increasing theeccentricity of its orbit and gradually bringing its point of perihelion closer to the surface of the Sun: according to the researchers, the comet is in fact doomed to collide with the Sun during the next two thousand years…