Mercury is the planet closest to the Sun in our Solar System. This small, rocky planet has almost no atmosphere. Mercury has a very elliptical orbit and a huge range in temperature. During the long daytime (which lasts 58.65 Earth days or almost an entire Mercurian year, which is 88 days long), the temperature is hotter than an oven; during the long night (the same length), the temperature is colder than a freezer. Mercury is a heavily cratered planet; its surface is similar to the surface of our Moon. Cratering on Mercury triggered volcanic eruptions that filled much of the surrounding area. Mercury does have a magnetic field (probably generated by a partly-liquid iron core). Mercury's thin atmosphere consist of trace amounts of hydrogen and helium. The atmospheric pressure is only a tiny fraction of the atmospheric pressure on Earth. Since the atmosphere is so light, the sky would appear pitch black (except for the sun, stars, and other planets, when visible), even during the day. Also, there is no "greenhouse effect" on Mercury. When the sun sets, the temperature drops very quickly since the atmosphere does not help retain the heat. Mercury has a huge range in temperatures. Its surface ranges in temperature from -270°F to 800°F. During the very long daytime, the temperatures are very high (the second-highest in the Solar System - only Venus is hotter); during the long night the thin atmosphere lets the heat dissipate, and the temperature drops quickly. Mercury is not well suited to host a prison. The temperature differation is too much. The high temperature is too high and the low is too low.

Venus is the hottest planet in our Solar System. This planet is covered with fast-moving sulphuric acid clouds which trap heat from the Sun. Its thick atmosphere is mostly carbon dioxide. Venus has an iron core but only a very weak magnetic field. This planet is uninhabitable due to the lack of oxygen, they would sufficate, they would die in the heat(average temp. 870), or they would be crushed by the massive atmosphiric pressure.

Mars is the most Earth-like planet in our solar system. It has a rocky surface with a thin atmosphere. It is dry and about half the size of Earth. The surface is covered in iron-rich dust and the southern hemisphere is all ice composed of frozen carbon dioxide and water. It was also discovered that there is liquid water on the surface. There is no oxygen though, so the planting of plants is needed to convert the carbon dioxide to oxygen. There is also craters that could help as a confinement center.

Jupiter's average temperature is -244 on the clouds. It is composed of mostly of gas. There is no oxygen and no evidence of a solid surface. Not a very likely choice for a prison.

Saturn's average temperature at the cloud tops is -290. There are 1,100 mph winds that blow to the east. Construction would be rather hard. Also there is no oxygen and no traces of water.

Uranus is surrounded by an icy cloud. Beneath the atmosphere, there is a liquid layer of hydrogen and helium. As depth increases, this layer becomes thicker, and then partly solid. This layer may be composed of compressed water with ammonia and methane. So there is water but still no oxygen and no sold surfaces to build on.

Neptune's thick atmosphere consists of 74% hydrogen, 25% helium and about 1% methane. Neptune's atmosphere has icy clouds and enormous storms. These features change rapidly because of tremendous winds that whip around the planet. Neptune has the fastest winds in our Solar System. Icy particles of methane in the outer parts of its atmosphere give Neptune its deep blue color. Neptune is composed mostly of ice, hydrogen and helium. It may have a small, rocky core, and an icy mantle that blends into the atmosphere. Neptune radiates almost three times as much heat energy as it gets from the distant Sun. Some of this excess heat is probably left over from the formation of this planet and some is generated by the slow collapse of the surface because of the planet's own gravitational forces.