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{{mergeto|terrestrial planet}}

A '''Super-Earth''' is a large [[extrasolar planet|extrasolar]] [[terrestrial planet]] more massive than the Earth but less than twenty times as massive. This range is by no means clearly defined, with various sources and authorities using differing mass ranges. A common lower bound is two Earth masses, and a common upper bound is ten Earth masses. <ref>sources vary: Valencia suggests less than 10, others 2 to 15, or 2-5 to 10</ref><ref>Peter N. Spotts. [http://www.thespec.com/article/188873 Canada's orbiting telescope tracks mystery 'super Earth'], ''[[Hamilton Spectator]]'', [[2007-04-28]]</ref><ref>http://space.newscientist.com/article/mg19626295.300-life-could-survive-longer-on-a-superearth.html</ref><ref name="Valencia">{{cite journal|first=Diana|last=Valencia|coauthors=Dimitar D. Sasselov, Richard J. O'Connell|year=2007|title=Radius and structure models of the first super-earth planet|journal=The Astrophysical Journal|volume=656|pages=545–551|doi=10.1086/509800}}</ref><ref>http://www.ice.csic.es/en/view_new.php?NID=18</ref>
A '''Super-Earth''' is a large [[extrasolar planet|extrasolar]] [[terrestrial planet]] more massive than the Earth but less than twenty times as massive. This range is by no means clearly defined, with various sources and authorities using differing mass ranges. A common lower bound is two Earth masses, and a common upper bound is ten Earth masses. <ref>sources vary: Valencia suggests less than 10, others 2 to 15, or 2-5 to 10</ref><ref>Peter N. Spotts. [http://www.thespec.com/article/188873 Canada's orbiting telescope tracks mystery 'super Earth'], ''[[Hamilton Spectator]]'', [[2007-04-28]]</ref><ref>http://space.newscientist.com/article/mg19626295.300-life-could-survive-longer-on-a-superearth.html</ref><ref name="Valencia">{{cite journal|first=Diana|last=Valencia|coauthors=Dimitar D. Sasselov, Richard J. O'Connell|year=2007|title=Radius and structure models of the first super-earth planet|journal=The Astrophysical Journal|volume=656|pages=545–551|doi=10.1086/509800}}</ref><ref>http://www.ice.csic.es/en/view_new.php?NID=18</ref>
Also, they are usually relatively close to their parent star(s), because colder, outer planets of that size would lose less gas during formation of a particular solar system and form into full [[Gas giant]]s.<ref>[http://arxiv.org/abs/astro-ph/0612671v3 ''Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits''], Fortney et al., April 2007</ref> The current popularized term "Super-Earth" is in fact a [[misnomer]], as by the preceding qualification they are usually more like [[Venus]] than [[Earth]].
Also, they are usually relatively close to their parent star(s), because colder, outer planets of that size would lose less gas during formation of a particular solar system and form into full [[Gas giant]]s.<ref>[http://arxiv.org/abs/astro-ph/0612671v3 ''Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits''], Fortney et al., April 2007</ref> The current popularized term "Super-Earth" is in fact a [[misnomer]], as by the preceding qualification they are usually more like [[Venus]] than [[Earth]].

Revision as of 12:58, 12 August 2008

A Super-Earth is a large extrasolar terrestrial planet more massive than the Earth but less than twenty times as massive. This range is by no means clearly defined, with various sources and authorities using differing mass ranges. A common lower bound is two Earth masses, and a common upper bound is ten Earth masses. [1][2][3][4][5] Also, they are usually relatively close to their parent star(s), because colder, outer planets of that size would lose less gas during formation of a particular solar system and form into full Gas giants.[6] The current popularized term "Super-Earth" is in fact a misnomer, as by the preceding qualification they are usually more like Venus than Earth.

There have been several discoveries of super-Earths since the 2005 discovery of Gliese 876 d by a team led by Eugenio Rivera. The Solar System does not contain examples of this category of planets, as the largest terrestrial planet in the Solar System is the Earth, and all larger planets have at least 14 times Earth's mass.

For planets such as Mu Arae d Super-Earth status has been calculated through computer models of planet formation, but there has been no confirmation through observation.

Discoveries

First super-Earth found

The first super-Earths were discovered by Wolszczan and Frail around the pulsar PSR B1257+12 in 1991. The two outer planets of the system have masses approximately 4 times that of Earth, too small to be gas giants.

The first super-Earth around a main sequence star was discovered by a team around Eugenio Rivera in 2005 and is orbiting Gliese 876 and received the designation Gliese 876 d (two Jupiter sized gas giants had been discovered in that system before). It has an estimated mass of 7.5 Earth masses and a very short orbital period of just about 2 days. Due to the proximity of Gliese 876 d to its host star, it has a high surface temperature of up to 650 kelvins. [7]

Other super-Earths discovered in 2006

Two further super-Earths were discovered in 2006, OGLE-2005-BLG-390Lb with a mass of 5.5 Earth masses, which was found by gravitational microlensing, and HD 69830 b with a mass of 10 Earth masses.[4]

First super-Earth in habitable zone

In April 2007, a team headed by Stephane Udry based in Switzerland announced the discovery of two new super-Earths around Gliese 581[8], both on the edge of the habitable zone around the star where liquid water may be possible on the surface. With Gliese 581 c having a mass of 5 Earth masses and a distance from Gliese 581 of 0.073 astronomical units or 11 million km, it is on the "warm" edge of the habitable zone around Gliese 581 with an estimated mean temperature (without taking into consideration effects from an atmosphere) of −3 degrees Celsius with an albedo comparable to Venus and 40 degrees Celsius with an albedo comparable to Earth.

Super-Earths found in 2008

The smallest Super-Earth found to date is MOA-2007-BLG-192Lb was announced by astrophysicist David Bennett for the international MOA collaboration on June 2, 2008.[9], [10] This planet has approximately 3.3 Earth masses and orbits a brown dwarf. It was detected by gravitational microlensing.

In June 2008, European researchers announced the discovery of three super-Earths around the star HD 40307, a star that is only slightly less massive than our Sun. The planets have at least the following minimum masses: 4.2 times Earth mass, 6.7 times Earth mass and 9.4 times Earth mass. The planets were detected by the radial velocity method by the HARPS instrument in Chile. [11]

In addition, the same European research team announced that they found a planet 7.5 times the mass of Earth orbiting the star HD 181433. This star also has a Jupiter-like planet that orbits every three years. [12]

Characteristics

Due to the larger mass of super-Earths, their physical characteristics differ from Earth's. A study on Gliese 876 d by a team around Diana Valencia[4] revealed that it would be possible to infer from a radius measured by the transit method of detecting planets and the mass of the relevant planet what the structural composition of a relevant super-Earth is. For Gliese 876 calculations range from 9,200 km (1.4 Earth radii) for a rocky planet and very large iron core to 12,500 km (2.0 Earth radii) for a watery and icy planet. Within this range of radii the super-Earth Gliese 876 d would have a surface gravity between 1.9g and 3.3g. High surface gravity (generally higher than Neptune and Saturn class planets and in certain circumstances higher than Jupiter class planets) is one of the predominant known characteristics of super-Earths.

Further theoretical work by Valencia and others suggests that Super-Earths would be more geologically active than Earth, with more vigorous plate tectonics due to thinner plates under more stress. In fact, their models suggested that Earth was itself a "borderline" case that was just barely large enough to sustain plate tectonics.[13]

See also

References

  1. ^ sources vary: Valencia suggests less than 10, others 2 to 15, or 2-5 to 10
  2. ^ Peter N. Spotts. Canada's orbiting telescope tracks mystery 'super Earth', Hamilton Spectator, 2007-04-28
  3. ^ http://space.newscientist.com/article/mg19626295.300-life-could-survive-longer-on-a-superearth.html
  4. ^ a b c Valencia, Diana (2007). "Radius and structure models of the first super-earth planet". The Astrophysical Journal. 656: 545–551. doi:10.1086/509800. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Cite error: The named reference "Valencia" was defined multiple times with different content (see the help page).
  5. ^ http://www.ice.csic.es/en/view_new.php?NID=18
  6. ^ Planetary Radii across Five Orders of Magnitude in Mass and Stellar Insolation: Application to Transits, Fortney et al., April 2007
  7. ^ 7.5 M Planet orbiting the nearby star GJj 876 Rivera et al., 2005
  8. ^ Udry; et al. (2007). "The HARPS search for southern extra-solar planets, XI. An habitable super-Earth (5 M⊕) in a 3-planet system" (PDF). Astronomy and Astrophysics. preprint: preprint. {{cite journal}}: Explicit use of et al. in: |author= (help)
  9. ^ http://www.abstractsonline.com/viewer/viewAbstract.asp?CKey={0B277B2C-9D4E-44A3-96FA-8A75EA22101D}&MKey={8460D0E8-0D41-43B0-9202-8630EAFEECBF}&AKey={AAF9AABA-B0FF-4235-8AEC-74F22FC76386}&SKey={56b1d6be-9060-4772-a2ed-639321105caf}
  10. ^ http://fr.arxiv.org/abs/0806.0025
  11. ^ http://news.bbc.co.uk/2/hi/science/nature/7457307.stm
  12. ^ http://afp.google.com/article/ALeqM5hhYYap4TAzGczvvDL51n97ryHo9A
  13. ^ CfA Press Release Release No.: 2008-02 January 09, 2008 Earth: A Borderline Planet for Life?
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