Nercury
The atmosphere is held in place by the earth's gravity. Gravity is related to mass, the more mass a planet has, the more gravity. A much smaller planet like mercury or a body such as the moon will have less gravity, not enough to hold an atmosphere - the gravity is not strong enough to prevent the gas particles from escaping into space.
For the same reason that our atmosphere on Earth does not escape into space - gravity.
For an object such as a planet or moon to have weather, it must have an atmosphere. Asteroids do not have strong enough gravity to maintain an atmosphere.
Gravity holds a planet's atmosphere close to its surface. The gravitational force of the planet's mass prevents the gases in the atmosphere from escaping into space. Without gravity, the atmosphere would disperse into space.
ya it has a little bit less gravity than the moon. its........floaty..........
Mercury - the closest planet to the sun. Solar wind and radiation from the sun also blast off some of Mercury's minuscule atmosphere (Mercury's atmosphere is sometimes referred to as an exosphere)
Mercury - the closest planet to the sun. Solar wind and radiation from the sun also blast off some of Mercury's minuscule atmosphere (Mercury's atmosphere is sometimes referred to as an exosphere)
The Earth has an atmosphere because it has the gravity necessary to keep the gases from floating off into space. The more mass a planet has, the more gravity it has, and the more gravity it has, the thicker an atmosphere it can sustain.
Gravity holds the atmosphere around the planet. Gravity is the force that attracts a body toward the center of the planet. For most purposes Newton's laws of gravity apply, with minor modifications to take the general theory of relativity into account.
Venus is the inner planet that has enough gravity to hold on to most gases. With a surface gravity about 90% that of Earth's, it can retain a thick atmosphere primarily composed of carbon dioxide, along with clouds of sulfuric acid. This dense atmosphere contributes to Venus's extreme greenhouse effect, resulting in surface temperatures hot enough to melt lead. In contrast, Mercury, the other inner planet, has too little gravity to retain a significant atmosphere.
The mass of the planet. It's not clear cut, since there has to be gas around in the area to provide the atmosphere, but the planet (or moon) need to be massive enough to provide sufficient gravity for the gas molecules not to escape into space.