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  • Explore the Solar System - Mercury

    by
    Maddog
    Published on 19-Dec-2011 05:37 PM
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    Mercury
    Mercury
    The innermost planet in the Solar System is a dense, heavily cratered world that takes about 59 Earth days to fully rotate on its own axis as it travels on its 88-day journey around the Sun.

    It is possible to see Mercury from the Earth without a telescope or binoculars though its closeness to the Sun's bright light can make it difficult to spot.

    Photographed and studied at close range by the Mariner 10 and Messenger probes, Mercury is blasted by solar radiation and is not thought to be a likely place for life to flourish.
    Photo: Mercury taken by the Messenger probe (NASA/JHU Applied Physics Laboratory/Carnegie Institution)
    About Mercury

    Mercury is the innermost and smallest planet in the Solar System,[a]orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits. The perihelion of Mercury's orbit precesses around the Sun at an excess of 43 arcseconds per century, a phenomenon that was explained in the 20th century by Albert Einstein's General Theory of Relativity. Mercury is bright when viewed from Earth, ranging from −2.3 to 5.7 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun is only 28.3°. Since Mercury is normally lost in the glare of the Sun, unless there is a solar eclipse it can be viewed from Earth's Northern Hemisphere only in morning or evening twilight, while its extreme elongations occur in declinations south of the celestial equator, such that it can be seen at favourable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky.

    Comparatively little is known about Mercury; ground-based telescopes reveal only an illuminated crescent with limited detail. The first of two spacecraft to visit the planet was Mariner 10, which mapped about 45% of the planet’s surface from 1974 to 1975. The second is the MESSENGER spacecraft, which attained orbit around Mercury on March 17, 2011, to map the rest of the planet.

    Mercury is similar in appearance to the Moon: it is heavily cratered with regions of smooth plains, has no natural satellites and no substantial atmosphere. Unlike the Moon, it has a large iron core, which generates a magnetic field about 1% as strong as that of the Earth. It is an exceptionally dense planet due to the large relative size of its core. Surface temperatures range from about 90 to 700 K (−183 °C to 427 °C), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest.

    Recorded observations of Mercury date back to at least the first millennium BC. Before the 4th century BC, Greek astronomers believed the planet to be two separate objects: one visible only at sunrise, which they called Apollo; the other visible only at sunset, which they called Hermes. The English name for the planet comes from the Romans, who named it after the Roman god Mercury, which they equated with the Greek Hermes (Ἑρμῆς). The astronomical symbol for Mercury is a stylized version of Hermes' caduceus.
    Mariner 10

    Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were allocated to the Voyager program and redesignated Voyager 1 and Voyager 2). The mission objectives were to measure Mercury's environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to obtain experience with a dual-planet gravity assist mission.
    Messenger

    The 2004 launch of NASA's Messenger probe marked the start of the first mission to the innermost planet in the Solar System since Mariner 10's three flybys in 1974. Messenger is looking at the side of Mercury that Mariner 10 couldn't photograph and is studying the planet's magnetic field and dense core, which is believed to make up at least 60% of its mass.

    Having completed a series of flybys, in 2011 it will enter a year-long orbit of the planet.

    A key mission goal is to explain why Mercury is the only inner planet besides the Earth to have a global magnetic field.
    Photo: Messenger prior to launch (NASA)
    About Messenger

    The Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The 485-kilogram (1,070 lb) spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury. It became the second mission after 1975's Mariner 10 to reach Mercury successfully when it made a flyby in January 2008, followed by a second flyby in October 2008, and a third flyby in September 2009.MESSENGER is furthermore the first spacecraft ever to orbit Mercury.

    The instruments carried by MESSENGER were tested on a complex series of flybys – the spacecraft flew by Earth once, Venus twice, and Mercury itself three times, allowing it to decelerate relative to Mercury with minimal fuel. MESSENGER successfully entered Mercury's orbit on March 18, 2011, and reactivated its science instruments on March 24, returning the first photo from Mercury orbit on March 29. MESSENGER's formal science data collection mission began on April 4, 2011.
    Facts about Mercury
    Check back tomorrow for the next planet in Explore the Solar System series: Venus




    Source: BBC

    This article was originally published in blog: Explore the Solar System - Mercury started by maddog

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