Mercury: The Planet With No Atmosphere
Mercury, the planet closest to the sun, has no atmosphere whatsoever. This means that the surface has no shielding from the vast amount of energy falling on its sunlit side and also has no ability to retain that heat on the dark side of the planet. Mercury has a daytime temperature of about 400 degrees celsius and a nighttime temperature of about -200 degrees celsius, a mere 73 degrees above absolute zero. That's a significantly low temperature for a planet so close to the sun, and it points out the significant role of our own atmosphere in keeping a relatively constant temperature on both the day and night sides of our world.
Also note that the surface of Mercury is covered with impact craters. With no atmosphere to impede or destroy meteorites, every single object that encounters the planet will hit it at full speed.NASA's Mercury Messenger probe recently confirmed that Mercury is volcanically active. The origin large smooth section of the crust shown in the first picture is unknown, but one suggestion is that a meteor of massive proportions nearly split the planet in two, prompting a large section of the crust to be replaced at once. Return from Mercury The Planet to Solar Greenhouse or return to the Green Planet home page for more Solar Power Facts.
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