At present there are around 540 extrasolar known planets. These are distant planets so not a lot is known about them, but there are some basic things that provide some basic information about them. It seems that the majority of them are planets that resemble Jupiter, being large and gaseous planets. It is very rare that a planet resembles Mars, in fact it is the rarest type of planets among the known planets so far. Even the planets that do share some characteristics with Mars, they also have characteristics that make them different, especially their size and distance from their star. Mars type of planets are very rare because of what Mars have actually become. The planet is assumed to have been similar to Earth, but its core has stopped its activity, resulting in no magnetism, and no volcanic activity. Also, the atmosphere of this planet is very thin, the temperatures vary greatly throughout the day, and its surface is covered with thick layers of dust and craters.
A warm front is indicated on the line by red semi-circles pointing away from the warmer air and pointing in the direction towards which the warm air is moving. Along sections of the polar front, cold and warm air masses may move differentially with for one another.
