Terrestrial planet

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Image:Terrestrial planet size comparisons.jpg
The inner planets, Mercury, Venus, Earth, and Mars, their sizes to scale.

A terrestrial planet, telluric planet or rocky planet is a planet that is primarily composed of silicate rocks. The terms are derived from Latin words for Earth (Terra and Tellus), so an alternative definition would be that these are planets which are, in some notable fashion, "Earth-like". They are the same thing as "Inner Planets."Terrestrial planets are substantially different from gas giants, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states.

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[edit] Structure

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. Terrestrial planets possess secondary atmospheres — atmospheres generated through internal vulcanism or comet impacts, as opposed to the gas giants, which possess primary atmospheres — atmospheres captured directly from the original solar nebula.

Theoretically, there are two types of terrestrial or rocky planets, one dominated by silicon compounds and another dominated by carbon compounds, like carbonaceous chondrite asteroids. These are the silicate planets and carbon planets (or "diamond planets") respectively.

[edit] Solar terrestrial planets

Earth's solar system has four terrestrial planets: Mercury, Venus, Earth and Mars, and one terrestrial dwarf planet, Ceres. Objects like Pluto are similar to terrestrial planets in the fact that they do have a solid surface, but are composed of more icy materials (see Ice dwarf). During the formation of the solar system, there were probably many more (planetesimals), but they have all merged with or been destroyed by the four remaining worlds in the solar nebula. Only one terrestrial planet, Earth, is known to have an active hydrosphere.

[edit] Extrasolar terrestrial planets

See also: Super-earth and Pulsar planet
Image:Earthlike planet-browse.jpg
SIM PlanetQuest will be able to detect Earth-sized planets, such as in this artist's rendering.

The majority of planets found outside our solar system to date have been gas giants, simply because gas giants are larger and therefore easier to see or infer from observation. However, a number of extrasolar planets are known or suspected to be terrestrial.

Aleksander Wolszczan detected the first extrasolar terrestrial planets. The three planets orbit the pulsar PSR B1257+12 with masses of 0.02, 4.3, and 3.9 times that of Earth's. They were discovered by accident: their transit caused interruptions in the pulsar's radio emissions (had they not been orbiting around a pulsar, they would not have been found).

When 51 Pegasi b, the first extrasolar planet found around a fusing star, was discovered, many astronomers assumed it must be a gigantic terrestrial, as it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. However, subsequent diameter measurements of a similar extrasolar planet (HD 209458 b), which transited its star showed that these objects were indeed gas giants.

In June 2005, the first planet around a fusing star that is almost certainly terrestrial was found orbiting around the red dwarf star Gliese 876, 15 light years away. That planet has a mass of 5 to 7 times that of earth and an orbital period of just two Earth days.

On 10 August, 2005, Probing Lensing Anomalies NETwork/Robotic Telescope Network (PLANET/RoboNet) and Optical Gravitational Lensing Experiment (OGLE) observed 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 newly discovered planet orbits its parent star at a distance similar to that of our solar system's asteroid belt. 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.

Image:Carbon Planet.JPG
Re-creation of carbon planet

In April 2007, a team of 11 European scientists announced the discovery of a planet outside our solar system that is potentially habitable, with Earth-like temperatures. The planet was discovered by the European Southern Observatory's telescope in La Silla, Chile, which has a special instrument that splits light to find wobbles in different wave lengths. Those wobbles can reveal the existence of other worlds. What they revealed is a planet circling the red dwarf star, Gliese 581. The discovery of the new planet, named Gliese 581 c, is sure to fuel studies of planets circling similar dim stars. About 80 percent of the stars near Earth are red dwarfs. The new planet is about five times heavier than Earth, classifying it as a super-earth. Its discoverers aren't certain if it is rocky, like Earth, or if it is a frozen ice ball with liquid water on the surface. If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball, it would be even bigger.

A number of telescopes capable of directly imaging extrasolar terrestrial planets are on the drawing board. These include the Terrestrial Planet Finder, Space Interferometry Mission, Darwin, New Worlds Mission, the kepler mission, and Overwhelmingly Large Telescope.

[edit] Most Earthlike exoplanets

Title Planet Star Notes
Closest planet to 1 MEarth PSR 1257+12 C PSR 1257+12 3.9 MEarth
Closest planet to 1 AU orbital HD 142 b HD 142 0.980 AU
HD 28185 b HD 28185 1.031 AU
HD 128311 b HD 128311 1.02 AU
Closest planet to 365-day orbit HD 142 b HD 142 337 d
HD 92788 b HD 92788 378 d
Closest to 300 K Mu Arae e Mu Arae 308 K
Gliese 581 c Gliese 581 290 K; A first Earth-like planet in habitable zone, possibility of liquid water.


[edit] See also

[edit] References

[edit] External links

 v • d • e The Solar System
<imagemap>

Image:Solar System XXVII.png

  1. The Sun

circle 0 0 90 35 The Sun

  1. Mercury

circle 112 18 6 Mercury

  1. Venus

circle 153 18 8 Venus

  1. Earth and the Moon

circle 203 8 4 The Moon circle 194 18 8 Earth

  1. Mars and satellites

circle 239 13 3 Phobos and Deimos circle 233 18 8 Mars

  1. Ceres and the asteroid belt
  2. - by placing the rectangle code for the asteroid belt AFTER Ceres, Ceres is "on top" (and can co-exist)

circle 271 18 8 Ceres rect 256 0 288 35 The asteroid belt

  1. Jupiter and satellites

circle 316 18 15 Jupiter circle 329 5 6 Moons of Jupiter

  1. Saturn and satellites

circle 372 18 10 Saturn circle 381 7 6 Moons of Saturn

  1. Uranus and satellites

circle 418 18 9 Uranus circle 427 10 6 Moons of Uranus

  1. Neptune and satellites

circle 471 10 3 Moons of Neptune circle 462 18 12 Neptune

  1. Pluto, satellites, and the Kuiper belt
  2. - by placing the rectangle code for the Kuiper belt AFTER Pluto, Pluto is "on top" (and can co-exist)

circle 508 13 3 Moons of Pluto circle 504 18 8 Pluto rect 492 0 527 35 The Kuiper Belt

  1. Eris, Dysnomia, and the Scattered disc
  2. - by placing the rectangle code for the Scattered disc AFTER Eris, Eris is "on top" (and can co-exist)

circle 544 14 3 Dysnomia circle 540 18 8 Eris rect 528 0 567 35 The Scattered Disc rect 568 0 597 35 The Oort Cloud

desc none

  1. - setting this to "bottom-right" will display a (rather large) icon linking to the graphic, if desired
  1. Notes:
  2. Details on the new coding for clickable images is here: [1]
  3. The smaller planets have a bit of an overlap just to ensure they're locatable, especially in the belts.
  4. While it may look strange, it's important to keep the codes for a particular system in order. The clickable coding treats the first object created in an area as the one on top.
  5. - I've placed moons on "top" so that their smaller circles won't disappear "under" their respective planets or dwarf planets.
  6. The "poly" code would be more appropriate for the moons of Jupiter, Saturn, and Uranus. However, there appears to be a bug with that aspect of the code.
  7. - I've compensated by using oversized circles for those moon groups, and tucking them UNDER their planets for now.
  8. The Sun is a rectangle as that approximates the edge closely enough for the purposes of this template.
  9. I've guessed as to the boundaries for the KB, SD, and OC - if they need adjustment, load the image into Paint and use the pencil tool to find the appropriate coordinates.

</imagemap>

The Sun · Mercury · Venus · Earth · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Eris
Planets · Dwarf planets · Moons: Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian · Plutonian · Eridian
Small bodies:   Meteoroids · Asteroids/Asteroid moons (Asteroid belt) · Centaurs · TNOs (Kuiper belt/Scattered disc) · Comets (Oort cloud)
See also astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Solar System Portal
zh-min-nan:Tē-kiû-hêng he̍k-chheⁿ

bg:Земеподобна планета ca:Planeta tel·lúric cs:Terestrická planeta de:Erdähnlicher Planet es:Planeta terrestre eo:Tersimila planedo fr:Planète tellurique ko:지구형 행성 hr:Terestrički planet it:Pianeta terrestre he:כוכב לכת ארצי mn:Хөрстэй гариг nl:Aardse planeet ja:地球型惑星 nn:Terrestrisk planet pl:Planeta skalista pt:Planeta telúrico ru:Планеты земной группы sk:Terestriálna planéta sl:Zemeljski planet sr:Терестричка планета fi:Maankaltainen planeetta sv:Stenplanet vi:Hành tinh kiểu Trái Đất tr:Yerbenzeri gezegen zh:类地行星

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