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Mercury experiences the most extreme temperature range of any of the planets. When Mercury is farthest from the Sun (at aphelion) the predawn temperature reaches a frigid -180°C (-300°F). As Mercury’s orbit reaches perihelion the mid-afternoon temperatures can skyrocket to 430°C (800°F). Mercury’s slow rotational period, its nearness to the Sun, and its lack of a substantial atmosphere are together responsible for this enormous variation in temperature. The period from sunrise to sunset lasts for 88 Earth days allowing the intense solar radiation to heat the surface. But during the nights (also 88 days long) the temperature falls dramatically since heat is not trapped within a thick atmosphere, as it is on Earth or Venus.

The seasons on Earth are caused by the tilt of its axis of rotation. Mercury’s axis is nearly perpendicular to the plane of it’s orbit, so it has no significant tilt and the planet has no seasons. The poles of Mercury never receive sunlight, and the temperature there remains below -160°C. It is here that scientists believe that frozen water may be found.

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Inside and Out
Odd but True...
Although Mercury is the closest planet to the Sun, it is not the hottest. That distinction goes to Venus, which has a surface temperature of about 460°C. This is due to the dense atmosphere of carbon dioxide, a very effective greenhouse gas. Solar radiation penetrates Venus' clouds and its heat become strapped.