If there are lots of craters, it means there is no significant atmosphere. The reason is that any craters will be eroded eventually, by the presence of 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.
Venus
You wouldn't be able to see the sky past the thick atmosphere. It would be quite foggy on the surface, but you would be able to see the rocky surface of the planet through the dense mist.
The atmosphere is above the surface of the Earth because gravity pulls it towards the planet. The atmosphere contains gases that are essential for life, such as oxygen and nitrogen, and it helps regulate the planet's temperature by trapping heat from the sun.
Mercury has a surface pressure that is near enough zero (or a vacuum), the planet holds no real atmosphere due to its small size. There are some trace gases at the surface, but not what one would call a proper atmosphere.
There are windstorms on the surface of Mars due to the heating of the atmosphere. Therefore, there would be wind erosion on the surface of Mars.
This depends on you definition of little. The best fit would probably be Mercury that has virtually no atmosphere and less than 40 % of Earth's gravity on the surface. (Until 2006 Pluto which has even less surface gravity was a planet as well but is now considered a dwarf planet)
Atmospheric pressure is an important factor in keeping liquid water on the surface of a planet. With no atmosphere, liquid water would quickly escape into space. It would depend on various factors such as the temperature and escape velocity of the planet of course. Scientists think liquid water existed on Mars in the past when the atmosphere was a lot denser. Water does exist on the surface Mars, but only as ice.
Yes, an atmosphere is necessary for a planet to have a greenhouse effect. The atmosphere traps heat from the planet's surface, creating a warming effect similar to a greenhouse. Without an atmosphere, there would be no mechanism to retain and redistribute heat, leading to extreme temperature fluctuations.
if we didn't have an atmosphere during the day our planet would be very hot and during the night our planet would be very cold
an asteroid would likely, if entering the atmosphere of a planet with a large gravitational force, break into smaller pieces while traveling through the outer atmosphere, and impact on the planet surface. On a planet with no atmosphere but a strong gravitational force, the asteroid would impact on the planet surface and likely break into pieces or become embedded in the surface. On a planet with little gravitational force, the asteroid would likely impact the surface, possibly break apart a bit, and float back up into space, or if the gravity is strong enough, slowly be pulled back to the surface, like a baseball falling in slow motion. On a planet like ours, if large enough, the effect could be devastating. On a planet like Jupiter, with its stronger than earth's gravity, would shoot through the 30 miles of surface gasses, and depending on rate of decent, be crushed by the weight of the atmosphere above it while passing through its 13,000 mile thick layer of hydrogen and helium, which changes from gas to liquid as depth and pressure increase, and may even make it to the 25,000 mile deep sea of liquid metallic hydrogen. On the moon it would likely skip off the planet's surface and go back into space, and depending on size either create a crater (such as the "man on the moon" group of craters on it now.) or break apart and skip off the surface and the smaller pieces would likely fall to the ground while the larger ones floated away, and since there is little atmosphere on the moon, the asteroid would not break apart while entering the atmosphere, as it would on earth with its dense atmosphere.
You're looking at the cloud tops of a gas giant, not the "true" surface of the planet. Actually we're not sure if there IS a surface, but Jupiter might well have a rocky and/or an icy core ... but the core would be tiny compared with the whole planet.