Mercury a planet

Mercury is the smallest planet in the solar system and closest to the sun. Mercury's orbit around the Sun takes 88 days. It ranges in brightness, but is not easily seen. It can only be seen in morning or evening twilight. Comparatively little is known about the planet: the only spacecraft to approach Mercury was the Mariner 10 from 1974 to 1975, which mapped only half the planet's heavily cratered surface. Mercury has no natural satellites and no substantial atmosphere. The planet has a large iron core which generates a tiny magnetic field. Mercury's surface is very similar in appearance to that of the Moon, showing extensive mare-like plains and heavy craters. Craters on Mercury range in diameter from a few meters to hundreds of kilometres across.  At the formation of the planet, Mercury was heavily bombarded by comets and asteroids for a period of time. During this period of intense crater formation, the planet received impacts over its entire surface without an atmosphere to slow impacting projectiles down.
Mercury is too small for its gravity to retain any significant atmosphere over long periods of time but it's magnetic field is strong enough to deflect the solar wind around the planet.
Observation of Mercury is complicated by its proximity to the Sun, as it is lost in the Sun's glare for much of the time. Mercury can be observed for only a brief period during either morning or evening twilight.
At greatest elongation west, Mercury rises earliest before the Sun, and at greatest elongation east, it sets latest after the Sun. The difficulties in observing Mercury mean that it has been far less studied than the other planets.

The only spacecraft to approach Mercury so far has been NASA's Mariner 10. The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury the first spacecraft to use this gravitational slingshot effect. Mariner 10 provided the first close-up images of Mercury's surface, which immediately showed its heavily cratered nature. The spacecraft made three close approaches to Mercury, the closest of which took it to within 327 km of the surface. At the first close approach, instruments detected a magnetic field, to the great surprise of planetary geologists Mercury's rotation was expected to be much too slow to generate a significant dynamo effect. The second close approach was primarily used for imaging, but at the third approach, extensive magnetic data were obtained. The data revealed that the planet's magnetic field is much like the Earth's, which deflects the solar wind around the planet. However, the origin of Mercury's magnetic field is still the subject of several competing theories. Just a few days after its final close approach, Mariner 10 ran out of fuel, its orbit could no longer be accurately controlled and mission controllers instructed the probe to shut itself down.

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. The MESSENGER spacecraft will make several close approaches to planets to place it onto the correct trajectory to reach an orbit around Mercury. It made a fly-by of the Earth in August 2005 and of Venus in October 2006 and June 2007. Three fly-bys of Mercury are scheduled, in January 2008, October 2008, and September 2009. The probe will then enter orbit around the planet in March 2011. The mission is designed to shed light on six key issues: Mercury's high density, its geological history, the nature of its magnetic field, the structure of its core, whether it really 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. Japan is planning a joint mission with the European Space Agency called BepiColombo, which will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere. An original plan to include a lander has been shelved. Russian Soyuz rockets will launch the probes in 2013. As with MESSENGER, the BepiColombo probes will make close approaches to other planets en route to Mercury, passing the Moon and Venus and making several approaches to Mercury before entering orbit. The probes will reach Mercury in about 2019, orbiting and charting its surface and magnetosphere for a year. The probes will carry a similar array of spectrometers to those on MESSENGER, and will study the planet at many different wavelengths including infrared, ultraviolet, X-ray and gamma ray. Apart from intensively studying the planet itself, mission planners also hope to use the probe's proximity to the Sun to test the predictions of General Relativity theory with improved accuracy.

Surface temperatures on Mercury range from about 180 to 430 °C.
Mercury has a diameter of about 4800 km at its equator.
Mercury consists of approximately 70% metallic and 30% silicate material.
Surrounding the core is a 600 km mantle.
Mercury's crust is thought to be 100 200 km thick.The image of mercury was produced from USGS I-1149, 1979. Higher resolution versions of the image can be downloaded from Mariner Mercury 10 Shaded Relief Map under the heading Orthographic View, centered at 0N latitude, 110W longitude
Url: ser.sese.asu.edu/M10/SHADE/shade_orth32.png

  •  Mean Radius:               2439.7 km
  •  Mass:                      0.055 (Earth=1)
  •  Density:                   5.43 (g/cm^3)
  •  Gravity:                   0.284 (Earth=1)
  •  Orbit Period:              87.97 (Earth days)
  •  Rotation Period:           58.65 (Earth days)
  •  Semimajor Axis of Orbit:   0.387 au
  •  Eccentricity of Orbit:     0.206
Mean Radius
Polar and sub-primary equatorial radii are given for irregularly shaped bodies whose root-mean-square deviation from an ellipsoid is known to be greater that 1% Radius given for gaseous bodies corresponds to a 1-bar surface
Mass
Earth's mass = 5.98x10^24 kg (6.578x10^21 tons)
Orbit Period
R = retrograde
Rotation Period
R = retrograde
Submajor Axis of Orbit
au = astronomical units 1 au = 149,599,000 kilometers (92,956,495 miles)
?
? = meaningful value can not be determined from available data

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date: 2007-09-20  Hits: