Mercury

    Mercury is the closest planet to the sun and the eighth largest. Its distance from the sun is approximately 58 million km (about 36 million miles). The diameter of Mercury is 4875 km (3030 mi) and its volume and mass are about 1/18 that of the earth. The temperatures is to be about 430° C (about 810° F) on the sunlit side and about –180° C (about –290° F) on the dark side. The force of gravity on the planet’s surface is about one-third of that on earth’s surface. Mercury is the second densest major body in the solar system, after Earth, but Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. This indicates that Mercury's dense iron core is relatively larger than Earth's. Mercury revolves about the sun in a period of 88 days. 

    The surface of Mercury consists of rough, porous, dark-colored rocks and is crisscrossed by long escarpments, dating perhaps from the period of contraction the planet experienced as it cooled some time early in its history when lava flooded the surface. This particular period of Mercury's history is called the Pre-Tolstoyan Period. This large surface formation was probably caused by an impacting asteroid with a diameter above 100 kilometers. It must have been a tremendously violent event. 

    Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km. The outer shell is only 500 to 600 km thick. At the time of the Pre-Tolstoyan Period, elements of comparatively low density like aluminum moved upwards into the uppermost part of the crust and on to the surface. At the same time, iron and other heavy elements moved downwards and formed a massive core at the center. At least some of the core is probably molten. Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. 

     Spectroscopic (an instrument for producing and observing spectra) studies indicate that only an extremely thin atmosphere, containing sodium and potassium, exists on Mercury. Its atoms are apparently diffusing from the crust of the planet. Scientists have detected a magnetic field surrounding Mercury, though it is not as strong as the field around the Earth. Scientists theorize that Mercury's field is due to an iron-bearing core or possibly to the solar winds. Although no trace of iron has been seen in spectroscopic studies of Mercury's surface, because of its presumably large iron core, this is very odd.

Features of Mercury

    Craters are indentations on planets, moons, and asteroids. Craters are formed by an asteroid or meteorite hitting the planet. The crater is mostly round. When the meteorite or asteroid hits the ground, the rock material that gets thrown out makes a ring around the spot where the meteorite hit. Mercury is a planet with many craters. The largest crater on Mercury is called Caloris Basin. Many craters on Mercury are named after famous people in history like Degas.

The Caloris Basin

    Caloris is Latin for heat and the basin is named this because it is near the global point (the point closest to the sun) when Mercury is at aphelion. The Caloris Basin is just north of the planet's equator and is surrounded by circular mountain ridges up to 2 km (6500 ft) high. It is 1,300 kilometers (810 miles) in diameter and is the largest known structure on Mercury. It was formed from an impact of a device with asteroid dimensions. The interior floor of the basin contains smooth plains but is highly ridged and fractured. It is covered by concentric "rings" of mountains - some of these ranges are 30 to 50 km long and form "rims" about 2 km high.

The Degas Craters

    The Degas Crater is 45 kilometer wide with bright rays coming from it which almost appear to be painted on. The rays consist of light colored material blasted out during the crater's formation.
Craters older than Degas are covered by the ray material while younger craters are seen superimposed on the rays. Mercury's gravity and density are about twice that of Earth's Moon so such bright ray craters on the lunar surface tend to be much larger.

Mercury         Venus         Earth         Mars         Jupiter         Saturn         Uranus         Neptune         Pluto