What is a Terrestrial Planet?
A terrestrial planet is a term used to describe the four planets in the solar system that are closest to the sun, Mercury, Venus, Earth and Mars. These four planets are composed primarily of rock and have solid surfaces. The word terrestrial is derived from the Latin word terra, meaning ground or soil. Besides a rocky, solid composition, the terrestrial planets share certain similar characteristics: • They are close to the sun. • They either have no moons or few moons. • They all have weak magnetic fields. • They all have closely spaced orbits • None of the planets have rings around them. The four other major planets, Jupiter, Saturn, Neptune and Uranus, in the solar system are referred to as gas planets or Jovian planets, after the planet Jupiter which is the largest planet in the solar system. The gas planets are much larger than the terrestrial planets and are composed mainly of gas and liquid. In contrast to the terrestrial planets, some characteristics of the gas planets are: • Th
The MESSENGER spacecraft will orbit Mercury following three flybys of that planet. The orbital phase will use the flyby information as an initial guide to perform a focused scientific investigation of this mysterious world. MESSENGER will enter Mercury orbit in March 2011 and carry out comprehensive measurements for one Earth year. The data-collection phase of the mission will conclude in March 2012. Mission Overview MESSENGER is a scientific investigation of the planet Mercury. Understanding Mercury, and the forces that have shaped it, is fundamental to understanding the terrestrial planets and their evolution. MESSENGER is a MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission to orbit Mercury following three flybys of that planet. The orbital phase will use the flyby data as an initial guide to perform a focused scientific investigation of this enigmatic world. MESSENGER will investigate key scientific questions regarding Mercurys characteristics and environment during t
It is a group of planets that are like Earth. The MESSENGER spacecraft will orbit Mercury following three flybys of that planet. The orbital phase will use the flyby information as an initial guide to perform a focused scientific investigation of this mysterious world. On a 4.9-billion mile (7.9-billion kilometer) journey that includes 15 loops around the Sun, the solar-powered MESSENGER will fly past Earth once, Venus twice and Mercury three times before easing into orbit around its target planet. The Earth flyby, a year after launch, and the Venus flybys, in October 2006 and June 2007, use the pull of the planets gravity to guide MESSENGER toward Mercurys orbit. The Mercury flybys in January 2008, October 2008 and September 2009 fine-tune and slow MESSENGERs track while allowing the spacecraft to gather data critical to planning the missions orbit phase. Primary mission at Mercury: Orbit for one Earth year (equivalent to four Mercury years, or two Mercury solar days), collecting data on t
