Can a comet erode?

Question

Is the tail of a comet a sign of erosion? How can it survive for millions of years?

Answer 1

Certainly. The tail is formed by comet material being warmed by the Sun and boiling away into space. Most comets are one time visitors, but some (like Halley and Encke) are periodic and revisit the inner solar system regularly, with increasingly disastrous effects on them. Comet Shoemaker-Levy 9 got close enough to Jupiter that gravitational effects broke it up and, on its next orbit it plunged into Jupiter. Most meteor showers are caused by the debris from old comets which have broken up.

Answer 2

Yes, comets are eroding and vanishing after a time. Scientists are aware that the lifetime expectancy of periodic comets is somewhere between 1000 to 10000 years.
Even if a comets comes into the vicinity of the sun only once every 70 year, and looses in only one of the 70 years some of its mass of dust and ice, and it's only 1% of its original mass per pass, then you can calculate that it is completely vanished in 7000 years. Many comets have a shorter period and most comets will loose more than 1% of their original mass per pass.
So comets are "short life" objects compared with the assumed age scale of the solar system. This fact is clear since more than 40 years. But instead of revising or questioning the assumed age of our solar system the science of cosmology "invented" the theory of the "Oort cloud" - a shell of "stand-by to be comets" chunks sitting far outside the orbit of Pluto, waiting to be attracted by the solar system and start their jurney towards the sun.
Oort's cloud has not yet been explored and not yet verified if it really exists.

Answer 3

Yes. The tail is made up of ice, dust and gas, that come from the erosion of the nucleus, or 'head'. This take place when in close proximity to the sun, as it goes around the sun. The sun melts the ice and heats up the 'core', giving off more particles. As it continues back out into space, it re-solidifies, making it less destructive. Most comets orbits are so big, the total time it is near the destructive power of the sun is very,very small compared to the total life of the comet. It takes eons to complete the destruction cycle.

Answer 4

Off-gassing regularly occurs with comets as they approach the Sun.

When they return to the nether regions of the Oort cloud, they do tend to pick up some of the icy matter out there by gravitational accretion and by tiny impaction. Since it's too far out and too dark to pick up, we can only hypothesize what affect the passage back out into the Oort Cloud will have on the mass and path of the comet, except to say that the expected cycle repeats with reasonable stability, unless acted upon by a significant external force/mass.

I don't think comets have been observed for more than a couple thousand years, so I think it is very premature to say that any of them last for MILLIONS of years.

Answer 5

Its a sign of melting. Erosion is usually caused by water or wind, typically from friction. There is little of that in space, but when a comet approaches a star, the ice begins to melt, and water and pieces break off.

Answer 6

Sorta, the sun's heat is melting it. And then the sun's solar wind is blowing the matter away from it.
I wouldn't say millions of years...but they last so long because the comets are only being melted for a fraction of their orbit. ex. the Hales comet's orbit is 72 years. For like one or two years, it's being melted. In the time that it isn't being melted, it's refreezing.