Comets. surrounded by a hydrogen cloud. comets.

Are comets and asteroids surrounded by hydrogen clouds?

In some comets, a cloud of hydrogen gas surrounds the coma. This hydrogen cloud may be as big as 3 million kilometers (about 2 million miles) across. When comets come near the Sun, their tails become visible because heat from the Sun vaporizes some of the icy nucleus or head and sunlight reflects from the vapor.

What is the atmosphere of an asteroid?

Asteroids have no atmosphere, but many are large enough to exert a gravitational pull — some, in fact, have one or two companion moons, or they form binary systems, in which two similarly sized asteroids orbit each other.