Super-Earth
Due to the proximity of Gliese 876 d to its host star (a red dwarf), it may have a surface temperature of 430–650 kelvin[16] and be too hot to support liquid water.
[17] In April 2007, a team headed by Stéphane Udry based in Switzerland announced the discovery of two new super-Earths within the Gliese 581 planetary system,[18] both on the edge of the habitable zone around the star where liquid water may be possible on the surface.
[21] In addition, the same European research team announced a planet 7.5 times the mass of Earth orbiting the star HD 181433.
The density estimate obtained for COROT-7b points to a composition including rocky silicate minerals similar to that of the Solar System's four inner planets, a new and significant discovery.
[26] A planet found in December 2009, GJ 1214 b, is 2.7 times as large as Earth and orbits a star much smaller and less luminous than the Sun.
"This planet probably does have liquid water," said David Charbonneau, a Harvard professor of astronomy and lead author of an article on the discovery.
On 24 August, astronomers using ESO's HARPS instrument announced the discovery of a planetary system with up to seven planets orbiting a Sun-like star, HD 10180, one of which, although not yet confirmed, has an estimated minimum mass of 1.35 ± 0.23 times that of Earth, which would be the lowest mass of any exoplanet found to date orbiting a main-sequence star.
The planet has a minimum mass 3.1 times that of Earth and a nearly circular orbit at 0.146 AU with a period of 36.6 days, placing it in the middle of the habitable zone where liquid water could exist and midway between the planets c and d. It was discovered using the radial velocity method by scientists at the University of California at Santa Cruz and the Carnegie Institution of Washington.
[38] Based on the latest Kepler findings, astronomer Seth Shostak estimates "within a thousand light-years of Earth" there are "at least 30,000 of these habitable worlds.
[44] On 5 December 2011, the Kepler space telescope discovered its first planet within the habitable zone or "Goldilocks region" of its Sun-like star.
On 5 December 2011, the Kepler team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter.
Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data.
[51] In April 2013, using observations by NASA's Kepler mission team led by William Borucki, of the agency's Ames Research Center, found five planets orbiting in the habitable zone of a Sun-like star, Kepler-62, 1,200 light years from Earth.
[52] On 25 June 2013, three "super Earth" planets have been found orbiting a nearby star at a distance where life in theory could exist, according to a record-breaking tally announced on Tuesday by the European Southern Observatory.
They are part of a cluster of as many as seven planets that circle Gliese 667C, one of three stars located a relatively close 22 light years from Earth in the constellation of Scorpio, it said.
The planets orbit Gliese 667C in the so-called Goldilocks Zone — a distance from the star at which the temperature is just right for water to exist in liquid form rather than being stripped away by stellar radiation or locked permanently in ice.
Instead of a primarily rocky composition, the more accurately determined mass of Kepler-10c suggests a world made almost entirely of volatiles, mainly water.
Three of the newly confirmed exoplanets were found to orbit within habitable zones of their related stars: two of the three, Kepler-438b and Kepler-442b, are near-Earth-size and likely rocky; the third, Kepler-440b, is a super-Earth.
The four-planet system, dubbed HD 219134, had been found 21 light years from Earth in the M-shaped northern hemisphere of constellation Cassiopeia, but it is not in the habitable zone of its star.
[60] Due to its closeness to Earth, Proxima b may be a flyby destination for a fleet of interstellar StarChip spacecraft currently being developed by the Breakthrough Starshot project.
[65] On 31 January 2024 NASA reported the discovery of a super-Earth called TOI-715 b located in the habitable zone of a red dwarf star about 137 light-years away.
It has been proposed that the presence of gas giants, namely Jupiter, might have prevented the inward migration of primordial Super-Earths into the inner Solar System.
Researchers at Harvard Astronomy Department have developed user-friendly online tools to characterize the bulk composition of the super-Earths.
[81] In particular, the complete removal of the primordial H/He envelope by energetic stellar photons appears almost inevitable in the case of Kepler-11b, regardless of its formation hypothesis.
[81] If a super-Earth is detectable by both the radial-velocity and the transit methods, then both its mass and its radius can be determined; thus its average bulk density can be calculated.
[9] Additional studies, conducted with lasers at the Lawrence Livermore National Laboratory and the OMEGA laboratory at the University of Rochester, show that the magnesium-silicate internal regions of the planet would undergo phase changes under the immense pressures and temperatures of a super-Earth planet, and that the different phases of this liquid magnesium silicate would separate into layers.
[88] These findings were corroborated by van Heck et al., who determined that plate tectonics may be more likely on super-Earths than on Earth itself, assuming similar composition.
Rather than evolving into a planet composed mainly of rock with a thin atmosphere, the small rocky core remains engulfed by its large hydrogen-rich envelope.
[94][95] The low densities inferred from observations imply that a fraction of the super-Earth population has substantial H/He envelopes, which may have been even more massive soon after formation.
Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures, which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles.
