Super Earth Planets

Super-Earth planets are planets with masses between 1 and 10 Earth masses. Such masses are still beyond the mass of the gas giants, e.g. the mass of Neptune is 17 MEarth- The atmospheres of such objects may be different from atmospheres for typical terrestrial planets. Some of them may possess hydrogen rich atmospheres. These objects should show strong H2O features in their spectra. Objects that have lost most of their hydrogen could exhibit strong CO2 features. Generally, this type of objects seems to represent a transition between rocky objects and Neptune-like planets. The discovery of super-Earths was discussed e.g. in Elkins-Tanton and Sea-ger, 2008 [120]. They argue that there are three ways how such objects may obtain atmospheres  

The habitability of super earths was discussed e.g. by Kaltenegger and Kasting, 2008 [177]. 

As we have mentioned in the chapter about meteorites, chondrites are the most primitive meteorite class. Hydrogen and oxygen are present mainly in the form of OH, the water content in the achondrites is lower (up to 3%). The degassing during accretion leads to a wide range of the mass of their possible atmospheres from less than 1% of the planet s total mass to 6% by mass of hydrogen, 20% of water and 5% of carbon compounds. Planets with deep surface liquid water oceans could have formed after the accretion has stopped. 

It is generally believed that super-earths may have a large variety of atmospheres. Some of them may even retain a hydrogen rich atmosphere (Miller-Ricci, Seager and Sasselov, 2009 [230]). Super-Earths with massive hydrogen atmospheres will reveal strong spectral features due to water, whereas those that have lost most of their hydrogen (and have no liquid ocean) will be marked by CO2 features and a lack of H2O. 

At least three planets with masses of 5.1, 18.2, and 24.0 MEarth seem to orbit the star 61 Vir which is of spectral type G5 V. This was deduced from 4.6 years of combined Keck/HIRES and Anglo-Australian Telescope precision radial velocities (Vogt et al., 2010 [347]). 

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Irwin, J., Charbonneau, D., Nutzman, P, Falco, E. The MEarth project searching fortransiting habitable super-Earth planets around nearby M-dwarfs. In Stempels, E. (ed.) American Institute of Physics Conference Series, vol. 1094, pp. 445-448 (2009)... 

Condie K. C. (1997) Episodic continental growth and super continents a mantle avalanche connection Earth Planet. Sci. Lett. 163, 97-108. 

Mahoney JJ, Sinton JM, Kurz MD, Macdougall JD, Spencer KJ, Lugmair GW (1994) Isotope and trace element characteristics of a super-fast spreading ridge East Pacific Rise, 13-23°S. Earth Planet Sci Lett 121 173-193... 

The discovery of transiting planets with masses below 10 MEanh and radii consistent with rocky planetary models answered the important question as to whether planets more massive than Earth could be rocky. 10 Mgarth and 2 Earth radii are used as estimates from planet formation theories as the upper limit for rocky planet mass and size. For comparison, Uranus has about 14.5 MEanh and about 4 Earth radii. Above about 10 Earth masses a planet is thought to accumulate a substantial amount of gas that makes it akin to a gas giant with a substantial atmosphere, not a rocky planet with a thin outgassed atmosphere. Where exactly such a cut-off mass is that distinguishes rocky Super-Earths and gaseous Mini-Neptunes - if it exists at all - is an open question that mean density measurements of detected exoplanets currently explore. 

The range of characteristics of planets is likely to exceed our experience with the planets and satellites in our own Solar System by far. Models of planets more massive than our Earth - rocky Super-Earths - need to consider the changing atmosphere structure, as well as the interior structure of the planet. Also, Earthlike planets orbiting stars of different spectral type might evolve differently. Modeling these influences will help to optimize the design of the proposed instruments to search for Earth-like planets. 

Udry S, Bonfils X, Delfosse X, Forveille T, Mayor M, Perrier C, Bouchy F, Lovis C, Pepe F, Queloz D, Bertaux J-L et al (2007) The HARPS search for southern extrasolar planets XI. Super-Earths (5 8 M Earth) in a 3-planet system. Astro Astrophy 469 43... 

Ford, E.B., Colon, K.D., Blake, C., Lee, B., Mahadevrm, S. First results of exoplanet observations with the Gran telescopio canatias narrow-band transit photometry capable of detecting super-earth-size planets. In Bulletin of the American Astronomical Society, vol. 41,... 

Mayor, M., Udry, S., Lovis, C., Repe, R, Queloz, D., Benz, W, Bertaux, J.-L., Bouchy, R, Mordasini, C., Segransan, D. The HARRS search for southern extra-solar planets. XIII. A planetary system with 3 super-Earths (4.2,6.9, and 9.2 M.). Astron. Astrophys. 493,639-644 (2009)... 

The Venus Express spacecraft launched by the European Space Agency (ESA) in November 2005 reached its goal in April 2006. Its main purpose was to find out more about the (still not understood) super-rotation of the Venusian atmosphere, which causes clouds to circulate the planet in about four earth days. Venus takes 243 earth days to rotate about its own axis. 

Another major property which leads to cosmochemical fractionation of the rare earths is that although they are refractory elements, they display significant variations in relative volatility. Sc, Y and Er are super-refractory elements, while Eu and Yb are notably more volatile than the remaining elements. This wide range in volatility is responsible for separation of the rare earths in high-temperature processes either in the early solar nebula, or in pre-solar events. Temperatures within planets are not extreme enough to cause such fractionations on the basis of volatility. 

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