Exoplanetary Scratchpad

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Within 50 Light Years

  • GJ 436 System (33.3 ly) - The second known red dwarf planetary system. Contains one of the first Neptunians discovered. 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. 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.
  • 55 Cancri System (40.1 ly) - Wide binary star consisting of a sun-like primary (A) 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 this many. It has three tightly packed eccentric planets close in to the star, including planet e (hot Super Earth/Neptunian), b (hot Jupiter), and c (hot Saturn). Planet e was the first Neptunian discovered. It was later found to be the shortest-period planet discovered (18 hours) and to transit. The planet has about half of Neptune's mass, but is Earth-like in size and density (2.17 Earth Radius). It is composed 70% of rock and the outer 30% is likely an ocean of super-critical water (between a gas and liquid state) that is 3000km thick. This is the hottest and densest super-Earth and the is the most watery planet found to date. It likely possesses a thick atmosphere of CO and CO2. 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. Planet f 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. The distant outer star causes planet d's axis to flip on its axis every million years. Planet d 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.
  • GJ 1214 System (42 ly) - 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. It is between Earth and Neptune in radius and it could be a small Neptunian, a terrestrial with an outgassed atmosphere, or a water world. Its featureless spectrum (the first Super Earth atmosphere ever studied) suggests a heavy atmosphere choked with water steam or one with thick water clouds above it, making viewing the surface impossible (further studies should resolve this). It may be the coolest transiting planet detected. Its close proximity (under 50 ly) assures promising future observation.

Within 100 Light Years

  • HD 189733 System (62.9 ly) - Planet b (the first nearby Very Hot Jupiter, originally thought to be inflated) is the nearest planet discovered using the transit technique (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. 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. Hubble found that its atmosphere was a uniform blue haze.
  • HD 97658 System (68.8 ly) - Also known as BD+26 2184, it is a nearby (68 ly) Yellow-orange star with a transiting low density sub-Neptune (6.3 ME, 2.7 RE) in a torch orbit. It has a Super Earth's mass, but a sub-Neptune's density and size. It is thought to have an extended atmosphere of Hydrogen, Helium, and Water. It was discovered with dopplar spectrometry and later found to transit.

Within 50 Parsecs

  • HAT-P-11 System (123 ly) - Star system with the second discovered transiting Super-Neptune and the least massive transiting planet known at the time. Also observed by Kepler and dubbed "Kepler 3b".
  • KOI-961 System (126 ly) - Nearby Red Dwarf Kepler star with three transiting planets in torch orbits smaller than the Earth. Planets are is c (~1.9 ME, 0.72 RE), b (~2.8 ME, 0.78 RE), and d (~0.95 ME, 0.57 RE, Earth-massed but Mars-sized). The planets have not been detected with dopplar spectrometry yet, so the masses and densities aren't known. Transits were detected independently and it is very unlikely the planets are not there. Nicknamed "Planets of the Apps" after a British amateur astronomer who alerted astronomers of the system's significance. The star was compared to Barnard's Star, in that they are both nearby and old. Comparison to this well known star assisted in the system's study. The system is comparable in scope to the Jovian system, more so than any other system.
  • HD 209458 System (153 ly) - Has first discovered transiting planet which was nicknamed Osiris due to the comet-like tail detected and the first exoplanet around a normal star to have its mass directly measured. 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. 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.

Within 100 Parsecs

  • HD 80606 System (190 ly) - Multiple star system with a planet, which has a higher period (111 days) than any other known transiting planet and highest eccentricty (Halley's comet-like). Discovered in 2001, but found to transit in 2009. Its orbit brings it from epistellar distances to Earth-like distances. 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.
  • HAT-P-20 System (70 pc) - A relatively nearby transiting exoplanetary system. It has a superjovian which has the second highest density of known planets at the time of its discovery.
  • HD 17156 System (78.24 pc) - Star system containing a planet discovered by dopplar spectrometry method and later found by amateurs to transit. At the time, it smashed the records for the furthest transiting planet (period of 21 d) and most eccentric orbit. A second, unconfirmed planet has also been proposed for this system.
  • HD 149026 System (78.9 pc) - Contains the first Saturn mass transiting planet. Also the first planet found with a dense core, leading credence to the core-accretion theory. Sometimes called a Super-Neptune, though it is not known if its core is rocky or icy. Also the first TEP discovered smaller than Jupiter. It was revealed to be as black as coal, twice as hot as any other known exoplanet, and hotter than some stars.
  • WASP-29 System (80 pc) - WASP-29 System
  • HAT-P-22 System (82 pc) - HAT-P-22 System
  • WASP-8 System (87 pc) - One of the 6 out of 27 planets analysed by the WASP team found to orbit backwards around its star in 2010.
  • HAT-P-17 System (90 pc) - HAT-P-17 System
  • WASP-10 System (90 pc) - System that contains a super Jupiter around an orange star. At first believed to be inflated, but later found to be smaller. Has a density similar to the moon. Has a candidate planet detected by the Transit Timing Variation method.
  • WASP-18 System (100 pc) - A hot F6 star that has Super Jupiter that is only 2.5 stellar radii from its host star. It may perish soon once it reaches its star's roche limit, but astronomers are puzzled why it hasn't already. Because it orbits much faster than its star rotates, tidal effects should be causing it to fall inwards. Further observations should reveal its rate of decay. Has the shortest period of any Hot Jupiter at the time of its discovery (22hours).

Beyond 100 Parsecs

  • Kepler-21 System (108 pc) - One of the brightest systems in Kepler's field of vision (though not quite visible to the naked eye, the nearest Kepler system with a confirmed planet), also known as HD 179070, located 352 light years away. Kepler detected a 10 Earth mass and 1.6 Earth radii hot super-Earth orbiting 10 times nearer than Mercury does the Sun. Its temperature is about 2,960F.
System P Mass Radius Density Gravity Distance Temp Star Disc
Mercury 0.06 ME 0.38 RE 5.427 g/cm3 3.7 m/s20.38 g[5] 0.38 AU

80 K 340 K 700 K

Venus 0.81 ME 0.95 RE 5.204 g/cm3 8.87 m/s20.904 g 635K
Earth 1.00 ME 1.00 RE 5.515 g/cm3 9.78 m/s2 1.00 AU 184 K 287.2 K 331 K
Mars 0.11 ME 0.53 RE 3.9
Jupiter 317 ME 11.2 RE 1.33

95 ME

0.3 MJ

9.4 RE

0.84 MJ

Uranus 14.5 ME 4.0 RE 1.27
Neptune 17.1 ME 3.88 RE 1.6
GJ 436 System b 23.4 ME 4.08 RE 1.51 1.18g 0.028 712K M2.5 2004
55 Cancri System e 8.58 ME 2.1 RE 5.9 0.016 5373K G8V / M3.5-4V 2004
GJ 1214 System b 6.3 ME 2.7 RE 1.87 g/cm3 0.91g 0.014 3026K M4.5 2009
HD 189733 System b 1.14 MJ 1.14 RJ 0.75 21.2 m/s² 0.031 1117K K1.5V/M 2005
HD 97658 System b 6.3 ME 2.9 RE 1.4 0.080
HAT-P-11 System b 25.7 ME 5.1 RE 1.4 0.053
KOI-961 System b 2.8 ME 0.78 RE 0.012
c 1.9 ME 0.72 RE 0.006
d 0.95 ME 0.57 RE 0.015
HD 209458 System b 0.71 MJ 1.4 RJ 0.047
HD 80606 System b 3.9 MJ 0.92 RJ 0.446
HAT-P-20 System b 7.2 MJ 0.87 RJ 0.036
HD 17156 System b 3.2 MJ 1.1 RJ 0.16
HD 149026 System b 0.36 MJ 0.72 RJ 0.043
WASP-29 System b 0.24 MJ 0.79 RJ 0.046
HAT-P-22 System b 2.1 MJ 1.08 RJ 0.041
WASP-8 System b 2.2 MJ 1.03 RJ 0.080
HAT-P-17 System b 0.53 MJ 1.01 RJ 0.088
WASP-10 System b 3.06 MJ 1.08 RJ 0.037
WASP-18 System b 10.4 MJ 1.16 RJ 0.020
Kepler-21 System b 10.5 1.6 RE 0.042

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