The Tidal Theory (or Chamberlain-Moulton Theory) suggests that a passing star pulled dust and debris from the forming Sun, leaving a string of debris that eventually formed the planets.

The planets make up only 0.135% of the mass in our solar system. The Sun dominates, accounting for 99.86% of the entire solar system's mass. Other factors include satellites (0.00004%) and comets (0.00003%).

Mercury & Venus are the only planets in our solar system without moons. Saturn has the most moons, with more than sixty.

Discovered by James Christy in 1978, Charon has a diameter of 1,172 kilometers (728 miles) and is just under half the size of Pluto. Due to this very small difference in size, some scientists consider Pluto and Charon to be a double (dwarf) planet.

The coma consists of gases and dust around the nucleus.

In 1963 Valentina Vladimirovna Tereshkova was selected from more than four hundred applicants and five finalists to pilot Vostok 6. She completed 48 orbits of the Earth in her three days in space.

Syzygy is the condition when three celestial bodies are arranged in a straight line--as, for example, when the Sun, Moon, and Earth are aligned during solar and lunar eclipses.

The first Apollo mission to circle the Moon was Apollo 8, and the first to land was Apollo 11. Apollo 13 never landed because of an accident en route that required the spacecraft to return to Earth after swinging around the far side of the Moon. The last Apollo mission to land on the Moon was Apollo 17.

Because of Pluto's irregular orbit, Neptune was actually the farthest planet from the Sun between 1978 and 1999.

Dust in the Martian atmosphere has fine particles that permit blue light to penetrate the atmosphere more efficiently than longer-wavelength colors.