The choice of "first" depends on definition and confirmation, as below. The three systems detected prior to 1994 each have a drawback, with Gamma Cephei b being unconfirmed until 2002; while the PSR B1257+12 planets orbit a pulsar. This leaves 51 Pegasi b (discovered and confirmed 1995) as the first confirmed exoplanet around a normal star.
First convincing exoplanet discovered around a Sun-like star.[2] While the minimum mass of HD 114762 b was high enough (11 Jupiter-masses) that it could be a brown dwarf, 51 Peg b's minimum mass meant that it almost certainly was near the mass of Jupiter.
First convincing exoplanet discovered around a Sun-like star.[2] While the minimum mass of HD 114762 b was high enough (11 Jupiter-masses) that it could be a brown dwarf, 51 Peg b's minimum mass meant that it almost certainly was near the mass of Jupiter.
[3] This was also the second planet detected through transiting,[3] and the then farthest planet known at time of discovery.[3] The first extrasolar planet detected to be transiting was HD 209458 b, which had already been discovered by the radial velocity method.[3][4]
Discovered by a light reflecting off of a dust cloud surrounding the planet.[8] First planet orbiting an ABO star. In 2020 this object was determined to be an expanding debris cloud from a collision of asteroids rather than a planet.[9]
First extrasolar planet discovered by astrometric observations
Detected through transit-timing variation method. Its existence was inferred by the gravitational influence it had on the orbital periodicity of Kepler-19b.[10][11]
First exoplanets discovered by orbital phase reflected light variations
Both transit timing variation and transit-duration variation was measured to measure deviations from the regular orbit of Kepler-88b. Deviations of the planet's transit duration and timing helped to discover Kepler-88c.[15]
By detection method
Some of these planets had already been discovered by another method but were the first to be detected by the listed method.
This first exoplanet found to be transiting had already been discovered by the radial velocity method. This is also the first planet that has been detected through more than one method.[3][4]
First directly imaged extrasolar planet (infrared)
May be a sub-brown dwarf instead of a planet, depending on formation mechanism and definitions chosen. If it is a planet, it is the first known planet around a brown dwarf.
First directly imaged extrasolar planet orbiting a 'normal' star (infrared)
Revised masses place it below the deuterium-burning limit.[16] May be a brown dwarf companion.[17]
DH Tauri b and GQ Lupi b were confirmed as companions within about three month in 2005. Both could be brown dwarfs. If one is a planet, it is the first planet orbiting a 'normal' star, possibly the first exoplanet directly imaged.
First directly imaged extrasolar planet orbiting a sun-like star (infrared)
GQ Lupi b was found earlier.[20] May, however, be a brown dwarf companion.
1RXS J160929.1−210524 b was found later.[21] Revised mass places it at or above the deuterium-burning limit. May be a sub-brown dwarf instead of a planet, depending on formation mechanism and definitions chosen. The orbital status of the companion was confirmed in 2010.[22]
First planet with observed secondary eclipse (infrared)
[24] also by [25] HD 189733 b was characterized spectroscopically only few month later.[26]
Any of the earlier Direct imaging exoplanets, e.g. 2M1207 b, DH Tauri b or GQ Lupi b have spatially resolved spectroscopic observations, but the objects need confirmation to be of planetary origin.
First planets directly characterized through astrometric observations
[28][29] Several spectra of Direct imaging exoplanets might be earlier, but the objects need confirmation to be of planetary origin. Especially AB Pictoris b is a candidate, if its mass is confirmed to be 10±1MJ.[19]
First planets detected through ellipsoidal light variations of the host star
Kepler-16b itself was detected through transit method. There are stars with earlier detections through eclipsing binary timing. However, either those signals have matched with unstable orbits or the exact orbits are not known.[33]
First planet detected by light variations due to relativistic beaming
"polarization of several tenths of a percent for DH Tau B and GSC 6214-210 B in H-band" ... "unlikely to be caused by interstellar dust." ... "the polarization most likely originates from circumsubstellar disks."[36] Both companions may be brown dwarfs or exoplanets.
Polarized scattered light was found for HD 189733 b in 2008.[37] It could not be confirmed and was disputed by two separate teams.[38][39][40] Possibly a "Saharan dust event over the La Palma observatory in 2008 August".[40] HD 189733 b was discovered in 2005.
By system type
First discovery by system type
System type
Planet
Star
Year
Notes
First extrasolar planet discovered in a solitary star system
Iota Draconis b / Hypatia was published in the very same month (September 2002) Gamma Cephei Ab / Tadmor was announced to be confirmed after initial discovery in 1988. While it is timewise a tie, the most recent mass estimate of 16.4 +9.3 −4.0MJ for Iota Draconis b, being likely above the deuterium burning limit, makes the 6.6 +2.3 −2.8MJGamma Cephei Ab more likely to be the first one.
First extrasolar planet discovered by visible light image. In 2020 this object was determined to be an expanding debris cloud from a collision of asteroids rather than a planet.[9]
First confirmed planet orbiting only a white dwarf.
Mu Arae c (discovered in 2004) has been proposed to be a terrestrial planet, but its terrestrial nature is not confirmed, as no radius measurements are available so the density is unknown. The minimum mass is comparable to that of Uranus, which is not a terrestrial planet. The first extrasolar planet found to have a density compatible with being a rocky planet is CoRoT-7b in 2009. 55 Cancri e was found to be a terrestrial planet in 2011.
Orbits a red dwarf star. The icy nature of this planet is not confirmed, as no radius measurements are available so the density is unknown. The first extrasolar planet known to have a density compatible with being an icy planet is GJ 1214 b, though even for this case there are other possibilities for the composition.
Orbits a red dwarf star. This planet orbits a little too far from the star, but the greenhouse effect would be enough to make this planet habitable. The other ocean planet candidate, GJ 1214 b, was detected by transit in which the density was calculated and determined that this planet is an ocean planet. Now disputed.[51][52]
The planet HAT-P-7b was discovered before WASP-17b, but its retrograde nature was announced after that of WASP-17b. The planet Nu Octantis Ab, whose orbit is retrograde in a close binary star, was suspected to exist since 2004 although it was not confirmed until 2021.[54]
First planet discovered orbiting a Sun-like star in a star cluster
^Charpinet, S. and Fontaine, G. and Brassard, P. and Green, EM and Van Grootel, V. and Randall, SK and Silvotti, R. and Baran, AS and Østensen, RH and Kawaler, SD; et al. (2011). "A compact system of small planets around a former red-giant star". Nature. 480 (7378). Nature Publishing Group: 496–499. Bibcode:2011Natur.480..496C. doi:10.1038/nature10631. PMID22193103. S2CID2213885.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Nesvorný, David; Kipping, David; Terrell, Dirk; Hartman, Joel; Bakos, Gáspár Á.; Buchhave, Lars A.; Stapelfeldt, Karl; Marois, Christian; Krist, John (2013). "Koi-142, the King of Transit Variations, is a Pair of Planets Near the 2:1 Resonance". The Astrophysical Journal. 777 (1): 3. arXiv:1304.4283. Bibcode:2013ApJ...777....3N. doi:10.1088/0004-637X/777/1/3. S2CID59933168.
^Mass was revised to about 11.5 Jupiter masses in 2006. [3][4][5]
^Barclay, Thomas; Huber, Daniel; Rowe, Jason F.; Fortney, Jonathan J.; Morley, Caroline V.; Quintana, Elisa V.; Fabrycky, Daniel C.; Barentsen, Geert; Bloemen, Steven; Christiansen, Jessie L.; Demory, Brice-Olivier; Fulton, Benjamin J.; Jenkins, Jon M.; Mullally, Fergal; Ragozzine, Darin; Seader, Shaun E.; Shporer, Avi; Tenenbaum, Peter; Thompson, Susan E. (2012). "Photometrically derived masses and radii of the planet and star in the TrES-2 system". The Astrophysical Journal. 761 (1): 53. arXiv:1210.4592. Bibcode:2012ApJ...761...53B. doi:10.1088/0004-637X/761/1/53.
^Knutson, Heather A.; David Charbonneau; Lori E. Allen; Jonathan J. Fortney; Eric Agol; Nicolas B. Cowan; Adam P. Showman; Curtis S. Cooper; S. Thomas Megeath (10 May 2007). "A map of the day–night contrast of the extrasolar planet HD 189733b". Nature. 447 (7141): 183–186. arXiv:0705.0993. Bibcode:2007Natur.447..183K. doi:10.1038/nature05782. PMID17495920. S2CID4402268.