Super Earths

Exoplanetary Scratchpad [SysBP Img]

"Super Earths" are planets with greater mass than Earth, but less that 10 times as massive. They can be rocky or gaseous. Some classifications use this to mean 1.25 to 2 times the size of Earth.

Super Earths In the News

Super Earths Will Have Plate Tectonics

• http://space.newscientist.com/article/mg19626255.500-superearths-will-have-plate-tectonics.html

Super Earths May Have Liquified Magnesium, Providing Protective Magnetic Shield (Nov 2012)

• http://news.discovery.com/space/exoplanet-super-earth-pressure-heat-metal-121122.html
• http://www.eurekalert.org/pub_releases/2012-11/ci-mof112112.php
• http://www.space.com/18604-super-earth-planets-liquid-metal.html

Hot Super Earths

Transit Detected

• CoRoT-Exo-7 System - A sunlike star about 500 light years away with two Hot Super Earths (and possibly a third), including the first detected transiting Super-Earth. It a diameter about twice that of the Earth. First exoplanet with evidence of a solid surface and does not possess a thick atmosphere. Because its star is active, its mass is somewhat uncertain (2.3 to 8.5 ME), which makes it unclear if the planet actually has a solid surface. Also the closest exoplanet to its star known and has the smallest orbit period (0.85 Earth Days). Likely the first Super-Io discovered (due to slight eccentricity) and the first gas giant remnant core found. Has temperature of 1000-1500C. Planet c is a larger Neptunian orbiting further away and does not transit.
• Kepler-10 System - An old sun-like star with a hot rocky Super-Earth (b) and a mega-Earth (c) in a Mercury like orbit. B is an airless Super-Earth covered in an ocean of magma with a high density, likely metallic. Its high density means its almost entirely composed of Silicate and metals. Had smallest measured diameter of any exoplanet (40% more than Earth, 4.5 Earth's mass, and nicknamed Vulcan by scientists) and is the first rocky exoplanet found by Kepler. Its daytime temperature is 1,500C, well over the melting point of Silicate and nearly that of Iron. The planet is glowing hot and lava pieces fly away from it like a cometary tail. Planet is similar to Corot-7b, but is around a more quiet star, making measurements more reliable, and thus this planet is the first certainly rocky planet discovered. Has circular orbit, so not likely a super-Io like that planet, instead considered a super-Mercury. Planet c was the first mega-Earth discovered and needed to be confirmed with the Spitzer telescope. Its diameter is 2.3 that of Earth and a mass of 17 that of Earth. It was thought rocky planets could get that big without absorbing enough gasses to make them gas giants. It is thought the planet never had an atmosphere because it is large enough to have kept it.
• 55 Cancri System - Copernicus is also known as Rho Cancri, 55 Cancri, Rho1 Cancri, HR 3522, Gl 324, and HD 75732. Wide binary star consisting of a sun-like primary (A, though super metal rich) and a red-dwarf secondary (B) separated by 1,100 AU, 41 light years away. Star A contains five exoplanets, the first system found with four or five planets. It has three tightly packed eccentric planets close in to the star, including planet Jannsen (e, hot Super Earth/Neptunian), Galileo (b, warm Jupiter), and Brahe (c, hot Saturn), followed by an eccentric Saturn in the habitable zone (Harriot, f) and a Jupiter analog, Lippershey (d). Planet e was heralded as the first Neptunian discovered. It was later found to be the shortest-period planet discovered (18 hours) and to transit. Its density was measured and determined to be rocky, and thus re-dubbed the first Super-Earth discovered. It was then the first super-Earth to have its light detected (by Spitzer in the infrared). The planet has about half of Neptune's mass, but is Earth-like in size and density (2.17 Earth Radius). Studies taking into account the composition of the star suggested that it was largely made of diamond, with graphite at the surface (the first diamond planet around a Sunlike star), and the first terrestrial found with fundamentally different surface composition and processes than Earth. This was later refuted when it turned out there wasn't as much carbon in the parent star as believed. Earlier studies that assumed an Earth-like composition suggested that it would be covered with an ocean of super-critical water. The brightness of the planet was found to have raised dramatically, possibly the aftermath of cloud cover due to a volcanic eruption. The brightness of the star (also closest known to transit and only known naked eye star to do so) makes it more easily studied than other hot super Earths. It was found to be dark and its sun-facing side hot enough to melt metal. It became the first super Earth to have its atmospheric composition measured (mostly hydrogen and helium with hints of hydrogen cyanide which would only dominate in a carbon-rich environment and no traces of water vapor) and temperature mapped, and the large hemispherical temperature differences suggest little atmosphere to transport heat. Planet b (one of the original 4 Hot Jupiters discovered) is the first "warm Jupiter" found to have a puffed up atmosphere and it probably at the outer limit from the star at which a planet can lose its atmosphere in this way. Its outer atmosphere skims the surface of the star, which was detected when attempting to detect an atmosphere around transiting Janssen. The strong interaction between planets Galileo and Brahe can be detected in measurements, and it took a while to find a fit that would allow them to survive over long periods of time. Harriot is a very eccentric Saturnian in the habitable zone. Planet d is a super jovian at Jupiter-like distances, which was the first found at true Jupiter distances and still the exoplanet discovered with dopplar spectrometry with the largest known semi-major axis. It was first thought to be circular, then eccentric, and then circular again. The distant outer star causes Lippershey's axis to flip on its axis every million years. Lippershey in turn causes the other planets to flip, including its star. The axis tilt of transiting planet e should be determined at some point. "Bode's law" predicts four undiscovered planets. One of the first 20 exoplanet systems allowed to be given common names by the IAU.
• Gliese 3470 System - Star containing a transiting hot super Earth (0.036 au, 3.3 days) discovered by HARPS. The star is small, so the ratio between stellar and planet radii is large. Atmospheric analysis (the second for any super Earth) indicated that it was not covered by thick clouds. Its radius was found to be 4.3 that of Earth. Detailed observation of its atmosphere are expected to be able to tell if it was formed close to the star or further out depending on if volatiles are found. Since the atmosphere is not likely blocked by clouds, it is thought that a detailed atmospheric composition can be taken.

Dopplar Spectrometry Only

• Gliese 876 System - Ross 780 is also known as Gl 876 and the flare star IL Aquarii. Very nearby quadruple planet system and the first Red Dwarf found to have planets. The innermost planet (d, Hot Superterran, rocky-water) was the first found rocky planet around a normal star (the first true Super-Earth, at epistellar distances). The outer three planets c (Warm Saturnian), b (Warm Jovian), and e (Cold Neptunian) are in 1:2:4 (30d/60d/120d) resonance (the exoplanet resonance and first triple-resonant planets discovered). The outermost planet has a Mercury-like orbit. Planet b is second discovered by ELODIE after 51 Peg b and the second to have its mass exactly measured and the first to have done so by astrometry.
• HD 156668 System - Contains a super-Earth that is second smallest exoplanet found with the dopplar method (after Gliese 581 e, 4 ME) at time of its discovery by Caltech astronomers at Mauna Kea. It had the smallest light amplitude detected using the dopplar spectrometry method. Found because of improved understanding of stellar phenomena that can mimic a planet.
• 61 Virginis System - A system containing a 5.1 ME Hot Super-Earth b (which is hot enough to have emissions on its night side) and one and possibly two other further out Neptunians (c and d [unconfirmed] and possibly a fourth), and a massive Kuiper Belt around a very Sun-like star only 28 light years away. All planets would fit inside Venus' orbit and have high eccentricities, especially the outermost one. This is the closest planetary system around a G-type star, which is one of the only very sun-like stars visible to the naked eye. It is the first non-borderline G-class main sequence star found to have a super-Earth. A lack of a Jovian planet and an unseen further out Neptunian may explain the large amount of cometary debris detected. Systems like this may avoid a heavy bombardment period, but instead undergo a steady rain of occasional cometary impacts for billions of year. Of the six sunlike stars within 10 parsecs, this star would be the one most likely to have an older version of Earth orbiting it. This postulated planet would have only microbes left as its star became hotter.
• HD 1461 System - A nearby (76 ly) yellow dwarf star with a hot super-Earth and possibly a Neptunian and a Saturnian further out. It and 61 Virginis are the first sunlike stars found to have Hot SuperEarths.
• HD 215497 System - Contains one of four super-Earths announced by the HARPs team in October 2009.
• Gliese 433 System - Contains one of four super-Earths announced by the HARPs team in October 2009.
• HD 7924 System - Nearby star with a super-Earth.
• HD 40307 System - A bright orange dwarf star with six known non-transiting super-Earth planets, including one of the most potentially habitable planets known. The star is about the same age as the Sun and is not magnetically active. The first three were announced with 45 other HARPS detected by Swiss team who discovered 51 Pegasus as part of the HARPs project. Early dynamic studies suggested these were smaller versions of Neptune, rather than larger versions of Earth. The next three were found by another team using a new method with existing data that threw out unreliable data. The inner 5 planets range from epistellar distances to half Mercury's distance. The outermost planet g orbits at Venus-like distances and is well within the habitable zone. It has a minimum of 7 times Earth's mass and receives 62% of the radiation Earth does. Liquid water could exist on the surface if it proves to be rocky. Unlike many other potentially habitable planets, it is not tidally locked. It is also by far the nearest potentially habitable planet around a sun-like star. It is a good future target for direct imaging. It was calculated that the planet might still have a magnetic field just barely strong enough to shield it from stellar radiation to protect its ocean.

Temperate Super Earths

Transit Detected

• GJ 1214 System - A red dwarf system containing the first exoplanet discovered by the MEarth project, which seeks to detect transiting Earth-like planets around nearby red dwarves, and the second transiting super-Earth. The planet is the first of a new class of planets with low mass and low density. Atmospheric observations suggest it is not a terrestrial with an outgassed (mostly Hydrogen/Helium) atmosphere, nor a Neptune-like world (Hydrogen/Methane mix). Instead it would be a new class of water worlds, with a bulk of its mass made of water. The temperature is too hot for liquid water and not thought to have a solid surface, so it could be covered with hot ice (plasma water). Its featureless spectrum (the first Super Earth atmosphere ever studied) prompted further investigation by Hubble. No chemical fingerprints were detected in its atmosphere despite high sensitivity, leading to conclusive evidence that high altitude clouds were preventing any detection (ruling out the possibility that heavier elements in the atmosphere were compressing the atmosphere, making it hard to detect, which may be the case for other planets with no detected chemicals). These are the first clouds proven around a super-Earth. It may be the coolest transiting planet detected. Its close proximity (under 50 ly) assures promising future observation.

Doppar Spectrometry Only

• HD 69830 System - First planetary system found that does not have a Jupiter-sized planet around a normal star (K0 spectrum). Contains 3 Neptunians and the first discovered asteroid belt that is like the size and age as the Sun's. The debris from this belt that was detected was from the breakup of an asteroid, is 20 times as massive as our own, and would cause zodiacal lights 1000 times brighter than we see from Earth. The smallest and outermost planet may be a 10 ME super Earth, is within the habitable zone, and is an inner shepherd for the asteroid belt. Halo 3 features a fictitious moon around this planet.
• Gliese 581 System - BD-11°3759 is better known as Gliese 581. Small nearby Red Dwarf with six planets in tight circular orbits. Several planets were announced in the habitable zone, but have since been retracted due to being due to sunspots rotating in view during it's 130 day rotation. E is the smallest known dopplar-detected exoplanet and a Super Mercury, b is a hot Neptunian, c is a super-Venus and the first detected in the HZ (initially heralded as habitable, but later thought too hot due to the greenhouse effect). G (1/4 stellar rotation) was the most controversial heralded as the first habitable Super-Earth and "Eyeball Earth", but was disproven. D (1/2 stellar rotation) was later thought to be an even more promising planet for life as it was big enough for a decent greenhouse effect even though it was at the outer edge of the habitable zone, was later thought to also not exist, but then its existence was re-affirmed. F was thought to be a cold super-Earth, but also disproven. The star is not very active. A massive Kuiper Belt was found, which may have been allowed to exist because the system lacks a Jovian class planet. A further out Neptunian may be responsible for the cometary collisions that produced the debris.
• Gliese 667 System- MLO 4 is most commonly known as Gliese 667 and also known as HR 6426 and HD 156384. A triple star system 23 light years away that contains planets in Scorpius. It was first cataloged as a binary star by astronomers at the old Melbourne Observatory (MLO) in Australia in 1867, so it was cataloged as MLO 4. It consisting of binary of orange dwarf stars about 12 AU apart (ranging from 5 to 20 AU), around which a distant red Dwarf C orbits (ranging from 56 to 215 AU). Star C is a dynamically packed planetary system, with at up to 7 unconfirmed super-Earth planets. The system became the nearest multistar system with planets when planet b (innermost, largest), a temperate super Earth planet (5.7 ME, 0.05 AU) was discovered, and is at the very inner edge of the most generous habitable zone. It became the poster child for an announcement of 32 exoplanets discovered by European astronomers working on the HARPs project and brought the total number of exoplanets to near 400. Planet c was later discovered near the inner edge of least generous habitable zone and is about the same size, and receives the same amount of stellar energy as the Earth. It was calculated that it likely no longer has a magnetic field that could protect its oceans from stellar radiation. Planets f and e were confirmed and also orbit in the Hz further out. Planet d is just beyond he HZ. Outermost planet, g (2.4 ME) is likely a frozen planet and the only one beyond Mercury-like distances. The multi-planet solution is somewhat lax and complicated and may need further confirmation. An even more unconfirmed planet h may be between b and c. A fourth stellar companion D is not gravitationally bound to the system.
• HD 181433 System - A triple planet system around an Orange dwarf star. Innermost planet is a super-Earth at Venus-like distances, without two Jovians orbiting further out. Super Earth was announced at the same time as the triple-Super-Earth system HD 40307 with the HARPS project.

Icy Super Earths

• OGLE-2005-BLG-390L System - Has first discovered Icy Super Earth, which was detected via Micro-lensing tens of thousands of light years away and was the smallest known exoplanet around a normal star at the time.
• MOA-2007-BLG-192L System - A very dim Red Dwarf star (once thought to be a potential Brown Dwarf) around which the smallest known exoplanet around a normal star (1.4 ME, once thought to be 3.3 ME) orbits. Orbiting at Venus-like distances, the planet is likely an icy frozen super-Earth.

Pulsar Super Earths

• PSR B1257+12 System - The first extrasolar system confirmed and one of the only planetary systems known around a pulsar. Has three rocky planets that orbit closer than Venus. The innermost has a Moon-like mass, while the next two out are Super Earths. May also have an outer "comet" sized body, the first sub-planetary object detected and possibly a representative of a mini "kuiper belt" at asteroid belt like distance.