Published on July 27, 2014
Mercury planet: Mercury planet BY MIDHUN KUMAR CLASS –VIIID ROLL NO-19 KV IITPOWAI History of mercury : History of mercury The first telescopic observations of Mercury were made by Galileo in the early 17th century . Although he observed phases when he looked at Venus, his telescope was not powerful enough to see the phases of Mercury. In 1631, Pierre Gassendi made the first telescopic observations of the transit of a planet across the Sun when he saw a transit of Mercury predicted by Johannes Kepler In 1639, Giovann Zupi used a telescope to discover that the planet had orbital phases similar to Venus and the Moon. The observation demonstrated conclusively that Mercury orbited around the Sun Information of Mercury : Information of Mercury Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, [a] with an orbital period of about 88 Earth days. Seen from the Earth, it appears to move around its orbit in about 116 days, which is much faster than any other planet. This rapid motion may have led to it being named after the Roman deity Mercury, the fast-flying messenger to the gods. Because it has almost no atmosphere to retain heat, Mercury's surface experiences the greatest temperature variation of all the planets, ranging from 100 K (−173 °C; −280 °F) at night to 700 K (427 °C; 800 °F) during the day at some equatorial regions. The poles are constantly below 180 K (−93 °C; −136 °F). Mercury's axis has the smallest tilt of any of the Solar System's planets (about 1 ⁄ 30 of a degree), but it has the largest orbital eccentricity. [a] At aphelion, Mercury is about 1.5 times as far from the Sun as it is at perihelion. Mercury's surface is heavily cratered and similar in appearance to the Moon, indicating that it has been geologically inactive for billions of years. Internal structure : Internal structure Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like the Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 km.  Mercury is even smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan. Mercury consists of approximately 70% metallic and 30% silicate material.  Mercury's density is the second highest in the Solar System at 5.427 g/cm 3 , only slightly less than Earth's density of 5.515 g/cm 3 .  If the effect of gravitational compression were to be factored out, the materials of which Mercury is made would be denser, with an uncompressed density of 5.3 g/cm 3 versus Earth's 4.4 g/cm 3 .  Orbit and rotation: Orbit and rotation Mercury has the most eccentric orbit of all the planets; its eccentricity is 0.21 with its distance from the Sun ranging from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi). It takes 87.969 earth days to complete an orbit. The diagram on the right illustrates the effects of the eccentricity, showing Mercury's orbit overlaid with a circular orbit having the same semi-major axis. The higher velocity of the planet when it is near perihelion is clear from the greater distance it covers in each 5-day interval. In the diagram the varying distance of Mercury to The Sun is represented by the size of the planet, which is inversely proportional to Mercury's distance from the Sun. This varying distance to the Sun, combined with a 3:2spin–orbit resonance of the planet's rotation around its axis, result in complex variations of the surface temperature.  This resonance makes a single day on Mercury last exactly two Mercury years, or about 176 Earth days.  Mercury's orbit is inclined by 7 degrees to the plane of Earth's orbit (the ecliptic), as shown in the diagram on the right. As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between the Earth and the Sun. This occurs about every seven years on average.  picture of mercury : picture of mercury Part of mercury : Part of mercury Mariner 10 : Mariner 10 The first spacecraft to visit Mercury was NASA's Mariner 10 (1974–1975).  The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury, making it both the first spacecraft to use this gravitational "slingshot" effect and the first NASA mission to visit multiple planets.  Mariner 10 provided the first close-up images of Mercury's surface, which immediately showed its heavily cratered nature, and revealed many other types of geological features, such as the giant scarps which were later ascribed to the effect of the planet shrinking slightly as its iron core cools.  Unfortunately, due to the length of Mariner 10's orbital period, the same face of the planet was lit at each of Mariner 10's close approaches. This made observation of both sides of the planet impossible,  and resulted in the mapping of less than 45% of the planet's surface.  Mariner 10 picture : Mariner 10 picture Messenger : Messenger A second NASA mission to Mercury, named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), was launched on August 3, 2004, from the Cape Canaveral Air Force Station aboard a Boeing Delta 2 rocket. It made a fly-by of the Earth in August 2005, and of Venus in October 2006 and June 2007 to place it onto the correct trajectory to reach an orbit around Mercury.  A first fly-by of Mercury occurred on January 14, 2008, a second on October 6, 2008,  and a third on September 29, 2009.  Most of the hemisphere not imaged by Mariner 10 has been mapped during these fly-bys. The probe successfully entered an elliptical orbit around the planet on March 18, 2011. The first orbital image of Mercury was obtained on March 29, 2011. The probe finished a one-year mapping mission,  and is now on a one-year extended mission expected to end in 2013. In addition to continued observations and mapping of Mercury, MESSENGER will observe the 2012 solar maximum.  The mission is designed to clear up six key issues: Mercury's high density, its geological history, the nature of its magnetic field, the structure of its core, whether it has ice at its poles, and where its tenuous atmosphere comes from. To this end, the probe is carrying imaging devices which will gather much higher resolution images of much more of the planet than Mariner 10, assorted spectrometers to determine abundances of elements in the crust, and magnetometers and devices to measure velocities of charged particles. Detailed measurements of tiny changes in the probe's velocity as it orbits will be used to infer details of the planet's interior structure.  MESSENGER: MESSENGER BepiColombo: BepiColombo The European Space Agency is planning a joint mission with Japan called BepiColombo, which will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere. Once launched in 2015, the spacecraft bus is expected to reach Mercury in 2019. The bus will release a magnetometer probe into an elliptical orbit, then chemical rockets will fire to deposit the mapper probe into a circular orbit. Both probes will operate for a terrestrial year. The mapper probe will carry an array of spectrometers similar to those on MESSENGER, and will study the planet at many different wavelengths including infrared, ultraviolet, X-ray and gamma ray.