Planets - Mercury

All about Mercury

The innermost planet is rarely seen because of the Sun's glare. With less than half Earth's gravity, Mercury retains only a wisp of an atmosphere (presumed to be helium). The lack of a significant atmosphere allows temperatures to fluctuate from 750 degrees Fahrenheit during the day to minus 320 Fahrenheit at night.

Like the other terrestrial planets -- Venus, Earth and Mars -- Mercury is made mostly of rock and metal. This small world is scarred by craters and looks somewhat like our Moon. This Mariner 10 image shows the density of craters.

Mercury data (averages):
Diameter: 3,031 miles
Time to rotate: 58.6 days
Orbit: 88 Earth days

Compared to Earth:
Mass: 5.5% of Earth's
Diameter: 38% of Earth's
Distance from Sun: 47% as far

MERCURIUS: ROMAN WINGED MESSENGER OF THE GODS

Historical notes

Mercury has been known since ancient times. Its elusiveness generated the name Hermes, given by the Greeks, later translated to Mercurius by the Romans.

Solar System

All About the Solar System



The solar system is the home to the sun, nine planets including the Earth, the 158 known moons that orbit those planets, as well as a countless number of other celestial bodies that exist throughout this vast space. Such celestial bodies include things like asteroids, meteoroids and comets.

Though the events leading up to the formation of the solar system are still being debated, is it believed to be more than 4.6 billion years old!

The word "solar" is derived from the Latin word for sun, Sol, leading to the term solar system, or the system of the sun. The planets that orbit the sun within the solar system include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and the smallest planet of Pluto. Jupiter is by far the largest with an overall mass of more than three times that of the Earth. The sun itself makes up an estimated 99.86% of the solar system’s total mass.

Gain further insight into the solar system by taking advantage of the solar system articles, solar system pictures or other interactive features below.