Terrestrial planet
From Free net encyclopedia
A terrestrial planet or telluric planet is a planet which is primarily composed of silicate rocks. The term is derived from the Latin word for Earth, "Terra", so an alternate definition would be that these are planets which are, in some notable fashion, "Earth-like". Terrestrial planets are substantially different from gas giants, which may not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets all have roughly the same structure: a central metallic core, mostly iron, with a surrounding silicate mantle. The Moon is similar, but lacks an iron core. Terrestrial planets have canyons, craters, mountains, and volcanoes.
Earth's solar system has four terrestrial planets: Mercury, Venus, Earth and Mars. At one time there were probably many more terrestrials, but most have been ejected from the solar system or otherwise destroyed. Only one terrestrial planet, Earth, is known to have an active hydrosphere.
NASA is considering a proposed project called the Terrestrial Planet Finder, which will be capable of detecting terrestrial planets outside of our solar system (orbiting other stars).
On 10 August, 2005, an international team of astronomers spotted the signature of a cold planet designated OGLE-2005-BLG-390Lb, about 5.5 times the mass of Earth, orbiting a star about 21,000 light years away in the constellation Scorpius. The planet revealed its existence through a technique known as gravitational microlensing, currently unique in its capability to detect cool planets with masses down to that of Earth. Prior to that, the smallest extrasolar planet discovered had been one of three known planets orbiting around the red dwarf star Gliese 876d, 15 light years away. That planet has a mass between six and nine times that of earth and is almost certainly a terrestrial planet.
Theoretically, there are two types of terrestrial or rocky planets, one dominated by silicon compounds, as Earth is, and another dominated by carbon compounds, like carbonaceous chondrite asteroids. These are the silicate planets and carbon planets (or "diamond planets") respectively.
See also
References
- Found: one Earth-like planet Astronomers use gravity lensing to spot homely planets. By Mark Peplow, News @ Nature.com, 25 January 2006.
- Beaulieu J.P., et al. (2006) Nature, 439, 437-440.
- National Science Foundation press release "Closer to Home."
- A New Path to New Earths National Science Foundation webcast.
- Ogling Distant Stars National Science Foundation grant report.
- PLANET Homepage.
- RoboNet Homepage.
- OGLE Homepage.
- MOA Homepage.
| edit The Solar System |
|---|
| Planets: Mercury - Venus - Earth (Moon) - Mars - Jupiter - Saturn - Uranus - Neptune - Pluto |
| Other: Sun - Asteroid belt - Main-belt comets - Kuiper belt - Scattered disc - Oort cloud |
| See also astronomical objects and the solar system's list of objects, sorted by radius or mass. |
zh-min-nan:Tē-kiû-hêng he̍k-chheⁿ ca:Planeta tel·lúric cs:Terestrická planeta de:Erdähnlicher Planet fr:Planète tellurique fi:Kiviplaneetta hr:Terestrički planet it:Pianeta terrestre nl:Aardse planeet ja:地球型惑星 pt:Planeta telúrico ru:Планеты земной группы sk:Terestriálna planéta sl:Zemeljski planet tr:Yerbenzeri gezegenler zh:类地行星