Correct me if I’m wrong, but I believe that the “tail” of a Comet is gas being released from the ball of ice junk. If a Comet is constantly degrading, how long is the typical lifespan? Is a Comet being built up from other space junk faster than it degrades?
The astronomers here will give you more solid answers, but basically, comets don’t last all that long.
Short-term comets (those whose orbits bring them into the inner Solar System every few years, like Comet Halley) only last about ten to twelve thousand years. Their lives are dependent upon how much mass they had to start and how short their orbit is. Every time they approach the Sun some of their volatiles are boiled away.
Cometary bodies whose orbits are not perturbed have been out there for as long as the Solar System has been around. About five billion years, give or take. The individual bodies could be a lot older than that, as they are remnants of the cloud of debris which collapsed to form the Sun and planets.
I believe the swarm of still frozen cometary bodies is called the Oort cloud. It is beyond the orbit of Neptune. Pluto seems to be the largest chunk of the stuff out there.
As time goes on, random collisions and gravitational interactions among the Oort cloud bodies cause some of them to fall into the gravity well of the Sun. Most of those just dive in once and return to the edges. Some few are captured into a shorter orbit, usually with assistence from Jupiter’s gravity, and these are the recurring comets astronomers can predict and whose “ashes” cause the predictable meteor showers like the Leonids.
Right, but the gasses are only released when the comet is heated up by being near the Sun. Also, since the orbits are very elliptical and very large, comets move much faster the nearer they are to the Sun so the amount of time that they are releasing gasses is small relative to the comet’s lifespan (they spend much less time near the Sun).
So basically they are not “constantly degrading”. They only lose mass during the short periods of time they are travelling near the Sun. Haley for instance has something like a 70 year period right? (I could be way off here) But it only spends a few weeks (or so) near the Sun.