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Exoplanets with Clouds Detected

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Exoplanetary Scratchpad

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List of exoplanets with evidence for cloud cover.

  • Kepler-7 System - One of first transiting exoplanets discovered by Kepler announced in a batch of 5 Jan 2010 (Kepler 4-9). It, like the others, is a hot Jupiter. It is the largest of the batch in diameter, its mass is 50% of Jupiter's, but its diameter is 50% greater than Jupiter, making its density that of styrofoam. This is the least dense planet found to date. It is also particularly bright for a Hot Jupiter, and has about three times the albedo of the typical one. This reflected light came from high altitude clouds in the west. Spitzer was able to measure the temperature of the bright spot in the hemisphere, which was too cool for a hot jupiter at this distance, so was interpreted as reflective clouds. The skies are clear on the east side, where it is hotter. The cloud structure, the first to be observed for an exoplanet, is stable over time. Being too hot for water clouds (though less hot than many Hot Jupiters), these clouds are probably made of silicates and magnesium. If made from perovskite or forsterite, the clouds could have a greenish tint.
  • Gliese 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.
  • Gliese 436 System - AC+27°28217 is best known as Gliese 436. The second known red dwarf planetary system. Contains one of the first Neptunians discovered and a few potential planets. The star is about half the sun's mass. It is over 11 Billion years old and may be a part of the old disk of the Milky Way. Planet b temporarily later found to be the smallest exoplanet (about Uranus' diameter, though over 50% its mass) known to transit its host star and is currently the nearest (33 ly). Its temperature (712K) was measured to be higher than what it would be purely from radiation (520K), perhaps due to a greenhouse effect, somewhat higher than Venus. It was originally thought to have a layer of "hot ice", water solidified due to high pressures. It turned out that it was larger than thought and hot ice was not needed. It could still be a rocky super-Earth. It was later found to have a remarkably low levels of Methane and high levels of Carbon Monoxide for its 800K temperature. Possible explanations include Methane being changed into hydrocarbon polymers due to its star's ultraviolet radiation, CO being drafted upwards with winds, or observational defects. Later, due to lack of detection of chemical signatures through the backlit atmosphere, it was concluded that high altitude clouds, perhaps made of potassium chloride or zink sulphide dust, were blocking the detection. This could be the first detection of clouds of a Neptunian. An alternate theory is that the atmosphere is filled with heavy compounds, such as water, carbond dioxide, which would compress the atmosphere and make it difficult to detect. After detection of a huge comet-like tail of Hydrogen trailing and wrapping around its orbit led to the most recent theory that it lost its Hydrogen to uv radiation and was left with a Helium dominated atmosphere with plenty of CO instead of CH4. It's significant eccentricity suggests a possible neighboring planet. Planet c was announced to be the smallest known exoplanet (1.5 Earth's diameter), but was later retracted because variations in transit timing of the first planet did not occur and the proposed orbit would be unstable. It is still thought that a second planet of some kind is possible in the system. Candidate UCF-1.01 was detected by a student in the UCF's astronomy department using the Spitzer Space Telescope. It is about 2/3 Earth's diameter (smaller than all but one confirmed exoplanet), orbits around its star in 1.5 days, and at 1000F may be a lava world without an atmosphere. UCF-1.02 also may exist. Both are thought to be about 1/3 as massive as the Earth, but are too small to get their mass measured and thus too small to be confirmed with present technology.

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