Mercury is the innermost of the eight planets in the Solar System. It is also the smallest, and its orbit has the highest eccentricity of the eight. It orbits the Sun once in about 88 Earth days, completing three rotations about its axis for every two orbits. Mercury has the smallest axial tilt of the Solar System planets.
Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It ranges in brightness from about −2.0 to 5.5 in apparent magnitude, but is not easily seen; its greatest angular separation from the Sun (greatest elongation) is only 28.3° (it can only be seen in twilight).
The diameter of Mercury is 4,879.4 km. It is only 38% the Earth’s diameter. In other words, you could put almost 3 Mercurys side to side to match the diameter of Earth.
Mercury is the smallest planet in the Solar System by surface area, volume, and equatorial diameter. Surprisingly, it is also one of the most dense. It gained its ‘smallest’ title after Pluto was demoted. That is why older material refers to Mercury as the second smallest planet.
If you weigh 100 pounds on Earth, you would only weigh 37 pounds on Mercury. Mercury has virtually no atmosphere. It however has small traces of an atmosphere which consists minute quantities of Hydrogen, Oxygen, Sodium, Potassium and argon.
Scientists have attempted to deduce the makeup of Mercury’s surface from studies of the sunlight reflected from different regions.
The surface of Mercury has landforms that indicate its crust may have contracted. They are long, sinuous scarps or cliffs called lobate scarps
Scientists now believe that the ice resides on the floors of craters at Mercury's north pole, where it can remain permanently shaded from the Sun and reach temperatures as low as 125 degrees Kelvin (-235 degrees Farenheit).
Mercury's hostile environs and barren surface have not earned it much love from Earth. With the exception of three flybys by the Mariner 10 spacecraft in 1974 and 1975, no NASA probe had bothered to pay a call.
On Saturday (March 17), MESSENGER completed its one-year primary mission, orbiting Mercury, capturing nearly 100,000 images and recording data that reveals new information about the planet's core, topography and the mysterious radar bright material in the permanently shadowed areas near the poles.
Astronomers used to dismiss Mercury, the planet closest to the sun, as mere "dead rock," little more than a target for cosmic collisions that shaped it, said MIT planetary scientist Maria Zuber. "Now, it's looking a lot more interesting," said Zuber, who has experiments on the Messenger probe. "It's an awful lot of volcanic material."
Both the solar-boiling and collision theories of Mercury's origins estimate that the surface of the planet would have reached temperatures up to 5,800°F (3,200°C). At that level of heat, however, potassium and thorium would have evaporated and uranium would have been depleted as well, combining with oxygen to form UO3.