Because they aren't traveling towards the sun. Comet tails are caused by debries being burned off.
Why do comets have tails
It's assumed those asteroids that once were comets have had the ice and dust burned off and now have nothing coming off to make a tail.
Comets
All comets have tails when their proximity to the sun is such that the icy debris in the comet is warmed enough to melt and fall away from the comet.
They are called comets.
Why do comets have tails
No, they do not burn only comets have tails.
No, that would be comets.
yes
Comets
rocks and dust
It's assumed those asteroids that once were comets have had the ice and dust burned off and now have nothing coming off to make a tail.
It depends on how fast the comet is going.
When they reach the inner solar system.
In the sense that an observer can see tails on comets - no, the gravity and composition of Mars is not favorable to the production of a tail.
yes
Comets