GJ 436 System (10.2 pc) - 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.
HD 189733 System (19.3 pc) - A binary star in Velpulca (the "little fox") consisting of an Orange Dwarf star A and a Red Dwarf B (discovered shortly after planet Ab found and orbiting perpendicular to that planet's orbit and later detected in x-rays) orbiting 216 AU away. Planet Ab (the first nearby Very Hot Jupiter, originally thought to be inflated, is 13% larger and more massive than Jupiter) is the nearest transiting Hot Jupiter (62.9 ly). This is the first exoplanet to have its temperature mapped and was nicknamed Bull's Eye for its hot spot that is significantly offset from the starward pole. 5 years later, it later became the first world to have its thermal emissions mapped in both longtitude and latitude, confirming the hot spot was near the equator. Fast winds are thought to make the temperature of the eternal day and night sides nearly identical, which were later measured to be 2km/s when the planet became the first to have its wind and weather patterns mapped. It is also the first exoplanet for which scattered light in the upper atmosphere has been detected and the second exoplanet with water detected and first with Methane and then Carbon Dioxide detected. It later was the first exoplanet whose gasses were detected from Earth-based telescopes. It was also found to spin up its star and magnetically interact with it, causing stellar storms. Massive X-class solar flares blast off much of the planet's atmosphere and may render it undetectable. Hubble found that its atmosphere was a uniform blue haze. Blue was detected by determining which wavelengths were blocked during a transit. It was also found to rain molten glass, sideways, with 7000 km/hr winds and 1000C. It became the first exoplanet whose transit was detected in X-Rays, which revealed it had a very large extended outer atmosphere, which is losing material rapidly. The star is much more magnetically active for its age, possibly due to the planet's presence. There is speculation that it could have large planet-wide auroras. It's already-known mass was measured using an atmospheric pressure method to test its viability. By studying sodium spectra, it was determined that it gets hotter with altitude.
HD 209458 System (47 pc) - Has first discovered transiting planet which was nicknamed Osiris due to the (first detected) comet-like tail detected and the first exoplanet around a normal star to have its mass directly measured. Also the first Inflated Hot Jupiter found. The planet may be losing its outer atmosphere, or magnetism may prevent the ions from escaping. They detected water in its atmosphere (they had failed earlier), the first time this has been done for any exoplanet. 2nd Exoplanet with detected organic compounds; like HD 189733b, it has water and carbon dioxide, but it has a lot more Methane. Was one of 2 planets to have light directly taken and thus their temperatures read (over 1000K). Tracking carbon molecules with dopplar spectrometry caused it to be the first exoplanet detected to have winds, which are raging at 5,000 to 10,000 km/h. This is believed to cause hotspots to appear at terminators rather than at the star-ward facing point. Had one of the strongest water detection of the 5 exoplanets contrasted by Hubble in 2013, though still less intense than expected, probably due to dust clouds or a haze blocking its detection.
HD 80606 System (58.4 pc) - Multiple star system (also known as Struve 1341) with a planet, which had a higher period (111 days) than any other known transiting planet and highest eccentricty (Halley's comet-like, epistellar distances to almost Earth-like distance) prior to the release of Kepler data. It is the nearest transiting Super Jupiter (4 MJ, radius slightly less than 1 RJ, 190ly). Its length of day is 36 hours. Discovered in 2001, but found to transit in 2009. Planet is the first one for which changes in weather have been observed. Potassium was detected from the high wind regions of the exosphere. In 2010 it was found to be only one of the two out of all 79 known transiting exoplanetary systems that could not support a habitable Earth-like planet, since its elongated orbit would destabilize any such planets. Planet thought to be in the process of becoming a Hot Jupiter. Observations suggested that energy transferred during closest approach to star would take 10 Billion Years to cause the orbit to circularize, meaning this tidal migration method may not be the preferred one to form hot jupiters.
1RXS1609 System (145 pc) - Contains first exoplanet (full name 1RXS J160929.1-210524) imaged around a sun-like star, photographed in 2008 and confirmed to orbit star in 2010. The planet's very large distance from the star 330 AU causes problems for planetary formation theories. Some liken it to an unbalanced binary star system where one component gobbled up the vast majority of the dust. It has about 8 times Jupiter's mass and 11 times Neptune's distance. It could be a new type of sub-stellar object between a planet and a Brown Dwarf. First exoplanet to have its spectrum taken, which revealed evidence of water, carbon monoxide, and hydrogen. Its star is young enough (5 MY) so that the planet has not had enough time to cool (1,500 C) and thus detectable.
XO-2 System (149 pc) - Contains a transiting planet. The planet is a little more than half Jupiter's mass, but is inflated to just above its radius. It was the first planet found to have Potassium detected, which is an element long thought to a dominant source for opacity in hot Jupiters.
WASP-12 System (427 pc) - The shortest period transiting Hot Jupiter known when discovered in 2008 and the first carbon-rich planet ever found (more Carbon than Oxygen). One of the two largest known planets at 1.79 Jupiter radii. Hottest known exoplanet at time of its discovery. Planet is being ripped apart by star. It is stretched in the shape of a rugby ball and leaves a ring around its star. Huge cloud of material detected around the planet containing elements never before detected on an exoplanet. This cloud is much larger than expected, and shrouds the entire star, making it undetectable at some wavelengths. Studying this cloud could reveal magnetic properties of the stellar system. Magnesium found in this shroud supports the blow-off theory where Hydrogen escapes from the planet so quickly other material is blown off with it. Two other Hot Jupiters are known to have planetary enveloping clouds, and others as close are expected to have similar system wide clouds, but not those further away. It has much more methane than water vapor. It may produce shock waves as it plows through its star's stellar wind (the first evidence of shocks around an exoplanet, like Earth and Saturn's bowshocks), possibly produced by a strong planetary magnetic field. This could protect its atmosphere from being stripped away. It could have a diamond core and other terrestrial planets in system would have black spots on them and also be carbon based. One of 5 exoplanets whose water abundance was measured by Hubble in 2013 and found to be less abundant than expected, probably due to a layer of haze or dust blocking detection..
WASP-17 System (?) - An F6 type star which has the first exoplanet discovered in a retrograde orbit. Also the largest known exoplanet at 1.74 RJ and 0.5 JM. Discovered by transit. It may be "flipping" its star's axis. Orbit hints at a near planetary collision in its early years. One of the 6 out of 27 planets analyzed by the WASP team found to orbit backwards around its star in 2010. It was found to be abundant in CO, depleted in water and methane. It lacks a prominent stratosphere and has efficient day-night energy circulation. Had one of the strongest water detection of the 5 exoplanets contrasted by Hubble in 2013, though still less intense than expected, probably due to dust clouds or a haze blocking its detection.
HR 8799 System - Hot young star system 300 ly away which is the only imaged and wide multiplanetary system. The 30 MY old star is the only known Gamma Doradus variable that is also a Vega-like star. The innermost is e (14.5 AU, 10 MJ), followed by d (24 AU, 10 MJ), c (38 AU, 10 MJ), and b (68 AU, 7 MJ). Inside the inner planet's orbit is an asteroid belt, while outside of the outer planet is a cometary belt (including a clump at 1:2 resonance with the outermost planet), while further yet is a huge halo extending to 2000 AU. The outer three are planets are 2-2.5 times as far as Saturn, Uranus, and Neptune are respectively, but receive similar radiation. The large planets would likely pull the system apart, leading scientists to believe the inner three planets are probably locked in a 1:2:4 orbital resonance in order to maintain stability. An inner planet is at Saturn-to-Uranus-like distances and challenges planetary formation models. Fomalhaut is the only other system where interaction between planets and dust belts can be observed. They are near the upper limits of mass to be classified as planets and could be Brown Dwarves. Upper mass limits are determined by system stability models. All three planets were later found in archived Hubble images. The middle planet became the first to have its spectrum directly measured. The spectrum confused scientists and didn't fit current formation theories. They contain carbon monoxide and are depleted in methane, which suggests they were formed in part by absorbing comets in the system. The outermost planet b has unusually thick dust clouds. There is possibly a fifth undetected planet in an inner resonant orbit.