Super-Earth

Super-Earth is a slang term for a large extrasolar terrestrial planets. It should be noted that the term depends only on the mass, but makes no claims as to the surface condition or habitability of the planet. The most common scale According must provide at least as heavy as the Earth, but lighter than the planet Uranus be, accordingly, the 1 - to 14 -fold have Earth's mass. Other common definitions put the 1 - to 10 - and 5 - to 10 -fold soil mass ahead. In addition, the planet is generally sufficient irradiated by the circled him star as it was a cold planet of this size only lose a little gas in this system arrangement and would be a gas planet.

There were isolated discoveries of super-Earths since the discovery of Gliese 876 d by a team led by Eugenio Rivera. The solar system contains no comparable planet, the largest terrestrial planet in the solar system is the earth; all larger planets have more than 14 Earth masses.

Various other planets, for example, My Arae d, have been proposed on the basis of computer simulations as super-Earths, however, turned out to these conjectures to be false.

Proof

Due to lack of accuracy of the measuring method, a Earth-like nature was far most extrasolar planets that have been classified in the group of super-Earths, not be unequivocally established. For planets with masses less than about 14 Earth masses, it is difficult to decide when a possibly existing dense gas envelope is counted no more than thick atmosphere, but as a gas shell around a solid core ( gas planet ). In order to decide whether it is a rocky planet or a hot Neptune so called, it is necessary to determine the average density of the object as accurately as possible. This is very difficult because it usually is only the lower limit of the possible mass of the known planetary mass due to the neglected and often unknown inclination.

The first unequivocally proven extrasolar rocky planet is discovered in early 2009 Planet CoRoT -7 b (formerly CoRoT- Exo -7 b). Meanwhile, with Kepler - 10b, a further proven rocky planet known. However, it is assumed that many more of the listed " super-Earths " have a terrestrial structure. The end of 2011 came with Kepler - 22b added a new candidate. Despite its small diameter, however, is not yet known whether it is a rocky planet is (as of December 2011).

Discoveries

In approximately 5 % of the exoplanets found so far is super-Earths. So far, less than 30 super-Earths are known.

In the future, their number could increase dramatically, all planet candidates the Kepler space telescope should be confirmed. From 1235 to early February 2011 discovered candidate if it were at 288 to super-Earths. 68 planets were approximately the size of the earth; 54 should be located in the habitable zone.

First super-Earth

The first super-Earths found by Wolszczan and Frail around the pulsar PSR B1257 12 in 1992. The pulses of the star arrived with regular delays what the scientists pointed out that he is accompanied by two satellites. For this type of measurement, it is the timing method. The two outer planets of four discovered satellites of the system have about 4 Earth masses, and are therefore too small for gas planet.

Other important super-Earths

The first super-Earth around a main sequence star was discovered by a team led by Eugenio Rivera 2005. The planet orbits Gliese 876 and Gliese 876 was designated as d ( two Jupiter- large planets had previously been discovered in the same system ). He is estimated to have at least the almost 6 times Earth's mass and a very short orbital period of just two days. Due to the close proximity of Gliese 876 d to its star, its surface has a temperature of 650 Kelvin.

Two further super-Earths were discovered in 2006: OGLE -2005- BLG - 390Lb with at least the 5.4 times the Earth's mass, which was discovered by the microlensing method, and HD 69830 b with at least 10 Earth masses. Both exoplanets orbiting each have a main sequence star, called a red dwarf.

In June 2008, David P. Bennett announced the discovery of the smallest exoplanet probably, MOA -2007- BLG -192 Lb, at a meeting of the American Astronomical Society known. This super-Earth has only 3.2 times as much mass as Earth and orbits a brown dwarf in the constellation Sagittarius. The approximately 300 light years distant planet probably consists mostly of ice and rock and was tracked by the microlensing effect.

In the same month the discovery of three super-Earths around Sun-like star HD 40307 in the constellation painter was known by the ESO. For the smallest planet in the 42 light-years distant star, the minimum mass is only about 4 Earth masses.

In early February, 2009, the Thuringian State Observatory, the discovery of an extrasolar rocky planet called CoRoT -7 b known. The only 1.75 Earth radii large planet was discovered in January with the help of the space telescope CoRoT by the transit method. The discovery is the first proven terrestrial exoplanets and therefore the first unequivocal super-Earth. With an orbital period of only about 20 hours, the planet holds another record. Due to its estimated mass and its proximity to its parent star, it was almost impossible that there is a gas or ice giants. Thus, it was thought that there must be an Earth-like planet. After lengthy observations and measurements with the HARPS instrument on the 3.6 -meter telescope at ESO, the presumption was confirmed in September of the same year. CoRoT -7 b accordingly has about 5 times the mass of Earth and a comparable mean density of the Earth.

In April 2009, Michel Mayor of the Geneva Observatory announced the discovery of the planet Gliese 581 e with only about 1.9 times the mass of Earth, he is so far the least massive exoplanet and already the fourth companion of Gliese 581 It is also very likely that there to 581 s is at Gliese a rocky world; he is after the detection of Earth-like structure of CoRoT -7 b the best candidate for a terrestrial planet.

The first two super-Earths around solar-type stars, 61 Vir b and HD 1461 b, were discovered in late 2009.

In early 2011, NASA confirmed the first discovery of a rocky planet through the space telescope Kepler. The Kepler - 10b -called exoplanet has 1.4 times the size and about 4.6 times the mass of our Earth. It is the smallest exoplanet yet discovered and has a density of 8.8 g/cm3, which is why it must be a terrestrial planet.

First super-Earths in the habitable zone

In April 2007, led by Stephane Udry team announced ( based in Switzerland ) the discovery of two new super-Earths around Gliese 581, both could exist in the habitable zone where liquid water. Gliese 581 c, which has five Earth masses and 0.073 AU or 11 million kilometers away from Gliese 581, located at the "warm" edge of the habitable zone around Gliese 581, with an estimated average temperature in (without atmospheric effects ) of -3 ° C a Venus -like albedo and 40 ° C at an Earth-like. He is the first Earth-like exoplanet with life-friendly temperatures.

According to recent computer models, some scientists Gliese 581 c, however, may be too hot to harbor liquid water. Then the exoplanet would be more like Venus and carbon dioxide and methane, warm the atmosphere by greenhouse effect above 100 ° C, so that no water would be expected in liquid form.

In contrast, Gliese 581 d, which was previously anticipated on the outer edge or outside the habitable zone, but after clarifying the path data is comfortable in April 2009 in her, now a serious candidate for liquid water.

In September 2010, scientists discovered two more exoplanets around Gliese 581, one of which, Gliese 581 g, is supposed to be Earth-like than any discovered so far. This exoplanet has the 1.2 - to 1.4 times the diameter of Earth and about 3 times the mass. It is located in the habitable zone and has a similar surface temperature of the Earth, however, it may be there due to the bound rotation strong temperature differences. However, It is still not sure if Gliese 581 g actually exists. A recent analysis of the data questions this.

Properties

Due to their higher mass have super-Earths of the earth different physical properties. In a study of Gliese 876 d by a team led by Diana Valencia, it turned out that it is possible to infer from the measured radius by the transit method, whether it is in the discovered planet is a super-Earth. For Gliese 876 calculations range from 9200 km (1.4 Earth radii ) for a rocky planet with a large iron core up to 12,500 km (2.0 Earth radii ) for a watery and icy planet. With this range of radii, the super-Earth Gliese 876 d could have a surface gravity between 1.9 g and 3.3 g. High surface gravity ( generally higher than Neptune and Saturn -sized planet and in some cases larger than Jupiter -sized planet ) is a prominent feature of super-Earths.

Further theoretical work from Valencia and others came to the conclusion that super-Earths are geologically active than the Earth, plate tectonics with stronger under higher loads. In fact, their models showed that the Earth itself is a " borderline " case and is just large enough to form plate tectonics.