Mercury also has little atmosphere. Scientists have detected the presence of atmospheric molecules, but there are so few molecules that it is hard to call it an atmsophere. With so little atmosphere, there cannot be a greenhouse effect to keep the temperatures warm and equally distributed between the side of Mercury which faces the Sun and the side of Mercury which faces away from the Sun. The side of Mercury which faces away from the Sun will be very cold because it is virtually directly exposed to space. The side of Mercury which faces the Sun will be very hot! This means that life forms would have to survive both the extreme heat as well as the extreme cold. That is hard to do.
Such life forms would also have to survive the extreme radiation (another name for "charged particles") found in the environment near the Sun. Such radiation has enough energy to break apart long molecules required by life, so it would be difficult for life to get started on Mercury. The magnetosphere of the Earth protects the Earth from these particles streaming away from the Sun. Mercury has a magnetosphere, but is it much smaller than the Earth's, and Mercury is much closer to the Sun.
You can leave the tour and read more about the greenhouse effect by leaving this tour and linking to the greenhouse effect at the bottom of this page. Or read about terrestrial bacteria called Archaea which can survive extreme heat.
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