Mercury is the innermost and smallest planet in the Solar System, 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 favorable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky.
Within the Asteroid Belt resides Mercury, Venus, Earth, Earth’s Moon, Venus, and Mars. Mercury is considered the Messenger, and symbolizes the god Hermes of Greece. Mars symbolizes Baal, and Venus as Ishtar the Queen Mother. The Earth’s Moon symbolize Nanna or Sin of the Mesopotamians. The symbolic feature draws to the three main Western religions. Judaism worships Baal, Christianity worships the Sun and the “Virgin Mother” (Ishtar), and Islam worships the Moon God Nanna.
According to NASA—MESSENGER, with its seven instruments, will be the first mission to orbit Mercury and only the second mission to visit this planet closest to the Sun. Understanding Mercury and its history is essential to understanding the origin and evolution of the other terrestrial planets. To get into orbit around Mercury, it must follow a complex path through the inner solar system, using one flyby of Earth, two flybys of Venus, and three flybys of Mercury for gravity assists. This impressive journey has already returned the first new data from Mercury in more than 30 years from its January 14, 2008 flyby.
MESSENGER launched on August 3, 2004, returned to Earth for a gravity boost on August 2, 2005, then flew past Venus on October 24, 2006 and June 5, 2007. It completed the first of three Mercury flybys on January 14, 2008 and will return on October 6, 2008 and September 29, 2009. The spacecraft uses these planetary flybys to resize and rotate its trajectory in order to achieve orbit around Mercury in March 2011. The Mercury flybys will also map the unseen side of the planet and yield science data to guide planning for the year-long orbital mission. MESSENGER’s instruments will map nearly the entire planet in color, image the surface in high resolution, and measure the composition of the surface, atmosphere and nature of the magnetic field and magnetosphere.
The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) probe is a 485-kilogram (1067 pound) robotic American space probe in orbit around the planet Mercury. The first space probe to reach Mercury was Mariner 10 in 1975.) MESSENGER is the first spacecraft to orbit the planet Mercury. Orbiting Mercury is difficult because a satellite approaching on a direct path from Earth would be accelerated by the Sun’s gravity and pass Mercury too quickly to orbit it.
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.
Maybe MESSENGER will run into Planet X on the way back to Earth?