Space Facts

Planet Mercury

Swift Moving Messenger of the Gods

Mercury as seen from the Messenger spacecraft, October 6, 2008, at a distance of 27,000 kilometers (17,000 miles). Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Mercury is planet number one of the Solar system. Named for the Roman messenger god (equivalent to the Greek god, Hermes), a deity also noted for trade, profit and commerce. Why the association? The planet moves rapidly, appearing as a morning star one day, and only days later appearing as an evening star. The gods would want their messenger to be fleet-footed.

Mercury is essentially an airless world, the only major Solar planet not to have more than a trace atmosphere. Because of this and its heavily cratered surface, it looks more like our moon. In fact, Mercury is only about 40% wider than Luna — 4880 kilometers (3030 miles) in diameter, compared to our moon's 3474 kilometers (2160 miles). It rotates once every 58.65 days, and orbits the sun once every 87.97 days. The slow rotation is a product of the sun's strong gravity and the resulting tidal forces within the solid body of the planet.

Size comparison of terrestrial planets with the Moon (left to right): Mercury, Venus, Earth, Luna and Mars.		The first four planets of the Solar system are called "terrestrials" because of their rough similarity to Earth. The other type of planet is called "gas giant," because the bulk of each such planet is gaseous. The Solar System Facts table gives more comparisons between the planets.

Could Mercury Ever Sustain Life?

A number of factors work against Mercury sustaining life. For one, it is so close to the sun. This makes it too hot (up to 420 °C, 788 °F), of course, but it also greatly slows the rotation of the planet. The long Mercurian days (58.65 Earth days long) would prove too hot by "noon" and too cold just before sunrise (-220 °C, -364 °F) to allow life to thrive, even if the planet were farther from the sun. A Mercury base might also have problems because of the slow rotation. If the base depended on solar power, it would have to wait a very long night for its next chance to recharge its power cells.

There are two exceptions, however. Both of the poles might be best suited for hosting Mercury bases. Both poles will have constant access to the sun because Mercury has an axial tilt of zero. Solar panels could be arrayed on a nearby hilltop or crater ridge allowing for continual power. What minerals does Mercury hold? It may be a long time before we find out. If Mercury ever does host a base for humans, we will likely need to bring most everything with us — air, water, food, plants, soil, and anything else deemed important for the survival and sanity of its inhabitants.

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