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Mercury

The innermost planet of the Solar System. In ancient Greece it had two names – Apollo for its appearance as a morning star and Hermes as an evening star – although Greek astronomers knew that a single body was involved. Being named after the fleet-footed god Hermes, or its Roman equivalent Mercury, is especially apt as the planet races around the Sun at an average speed of 48 km/s, completing one circuit in 88 days. Until the 1960s it was thought that Mercury's day (the time it takes to spin on its axis) was the same length as its year (the time it takes to complete one orbit) so that it always kept one face to the Sun. However, Doppler radar measurements in 1965 showed that Mercury actually rotates three times in two of its years. Although Mercury's mean distance from the Sun is 57,910,000 km (0.387 AU), its orbit is very elongated. The range from perihelion to aphelion is 46 to 70 million km.

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(Source: The Internet Encyclopedia of Science »)

  • Mercury - Overview Featured Article Mercury - Overview Mercury - Overview

    Mercury's elliptical orbit takes the small planet as close as 47 million kilometers (29 million miles) and as far as 70 million kilometers (43 million miles) from the Sun. If one... More »

  • MESSENGER Featured Article MESSENGER MESSENGER

    MESSENGER is a scientific investigation of Mercury, the least explored of the terrestrial rocky planets that also include Venus, Earth and Mars. Understanding Mercury and how it... More »

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MESSENGER Last Updated on 2009-09-28 17:20:38 MESSENGER is a scientific investigation of Mercury, the least explored of the terrestrial rocky planets that also include Venus, Earth and Mars. Understanding Mercury and how it formed is critical to better understanding the conditions on and evolution of the inner planets. The project takes advantage of clever mission designs, tougher lightweight materials and miniature technologies all developed in the three decades since Mariner 10 flew past Mercury. The compact orbiter, fortified against the searing conditions near the Sun, will investigate key questions about Mercury's characteristics and environment with a set of seven scientific instruments. MESSENGER matched Mercury's orbit with a series of flybys of Earth, Venus and Mercury, using gravity to adjust its path each time. Three Mercury flybys, which will included photographing and measurements of the planet's previously unseen... More »
Mercury - Details Last Updated on 2009-03-17 00:00:00 Mercury's elliptical orbit takes the small planet as close as 47 million kilometers (29 million miles) and as far as 70 million kilometers (43 million miles) from the Sun. If one could stand on the scorching surface of Mercury when it is at its closest point to the Sun, our star would appear more than three times as large as it does when viewed from Earth. Temperatures on Mercury's surface can reach 430°C (800°F). Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -180°C (-290°F). Because Mercury is so close to the Sun, it is hard to directly observe from Earth except during twilight.     Mercury makes an appearance indirectly, however - 13 times each century, Earth observers can watch Mercury pass across the face of the Sun, an event called... More »
Mercury - Overview Last Updated on 2008-12-22 00:00:00 Mercury's elliptical orbit takes the small planet as close as 47 million kilometers (29 million miles) and as far as 70 million kilometers (43 million miles) from the Sun. If one could stand on the scorching surface of Mercury when it is at its closest approach, the Sun would appear almost three times as large as it does when viewed from Earth. Temperatures on Mercury's surface can reach 430 degrees Celsius (800 degrees Fahrenheit). Because the planet has no atmosphere to retain that heat, nighttime temperatures on the surface can drop to -170 degrees Celsius (-280 degrees Fahrenheit). Because Mercury is so close to the Sun, it is hard to directly observe from Earth, except during twilight. Mercury makes an appearance indirectly, however 13 times each century, Earth observers can watch Mercury pass across the face of the Sun, an event called a transit. These rare transits fall within... More »