Are the comets alive?
D. Anton

The behavior of comets is unpredictable. They appear out of nowhere, they submerge inside the solar system, sublimate their ice, eject strong jets from their surfaces, eject dust particles that are swept away by the solar wind forming a "comma" or a "tail."
They are very dark, almost black, their albedo is less than 5%. They are darker than coal. Its ice is water, carbon dioxide and various hydrocarbons and organic compounds and molecules.
They change their brightness for no apparent reason.
Fred Hoyle, Chandra Wikramasinghe and others believe that bacterial spores exist within comets and that life came to Earth within these celestial bodies (theory called "panspermia"). Occasionally new comets hit our planet. This is probably what happened in Tunguska, Siberia, in 1908.
It is possible that comets not only transport life, in the form of bacteria or spores, they may even be alive themselves. Somehow they match the definition of a living "organism." They are born when they leave the frozen interstellar environment and begin their activity during their solar drift. They die when they get too close to the sun or after a few thousand orbits near Earth or other inner planets. Some of them have elliptical orbits and other parabolic or hyperbolic orbits. When they get too close to the sun, their ice sublimate and may disappear in the solar heat or disarticulate into smaller pieces, leaving them as tiny remains and falling on Earth, from time to time, in the form of meteorites ...
The few interplanetary probes that visited the comets have confirmed their unusual characteristics, especially the impressive Rosetta mission, which went to accompany comet 67 / Churyurmov-Geramisenko in its orbit. Several organic molecules were identified during this mission and there are still many doubts about the internal dynamics of these small and mysterious space bodies.
A weirdo comet that appeared recently

Recently, at the end of August 2019, a comet whose origin is outside the solar system (the first one registered with that provenance) was spotted. Its official name is 2I / Borisov, the last object to approach our cosmic neighborhood from a very distant place.
Investigators have been tracking the object since it was discovered on August 30 by an amateur astronomer in Crimea named Gennady Borisov. And that's where the second part of the name of this object comes in: the object Borisov was tracking through his 0.65-meter home telescope looked like a comet, with a distinctive haze or "comma." Comets, unlike asteroids, moons or other spatial characteristics, are usually named after their discoverer, which makes the designation
2I / Borisov apppears to be a comet, with a short tail already visible to astronomers. The comet, which is estimated to be a few kilometers in diameter, will make its closest approach to the Sun on December 7, 2019, before it begins to withdraw from the Solar System. That gives astronomers a generous amount of time to track this interstellar visitor and, hopefully, learn more about where it is and what it is made of, before it finally disappears.