courtesy of Eric Mamajek
The below extrasolar systems are listed in order of discovery.
Currently there is no clear definition of a planet. The systems listed below are of objects that have been confirmed by several sources and/or techniques and are believed to be planets because their mass is less than that necessary to ignite deuterium burning.
Wolszczan and Frail's discovery of the first planetary system outside of our own. Two terrestrial-mass planets were initially discovered in 1991 (A,B), a third moon-sized body (C) was later found (1994), and yet a possible 4th Saturn-mass planet (D) has been inferred in the data up until 1996 (Wolszczan (1996) & Joshi & Rasio (1996)). The planets were discovered via the pulsar-timing method, and pose a mystery for astrophysicists. How can planets form in such an environment? Did they accrete and form after the supernova?
The first of the confirmed jovian planets discovered orbiting a nearby, solar-type star. 51 Peg b is also the first confirmed exoplanet found via doppler spectroscopy. This discovery broke astronomer's expectations of where jovians can exist. Some quick calculations show that the object should be able to retain an atmosphere, despite its subsolar temperature of roughly 1200K.
The prototype of the "eccentric"-type planets (Marcy & Butler 1996). This behemoth of a world orbits a solar-type star in a very eccentric orbit (e=.40). It appears to be either a low-mass brown dwarf or a very massive jovian planet. The eccentricity of the planet's orbit and its large mass likely precluded the formation of planets within many AU of its star. This was the first announced detection of many from the San Francisco State Planet Search group using Lick Observatory. This object seems to be akin to HD 114762 in nature.
47 Ursae Majoris
This is the first extrasolar planet discovered that partially resembles our own Jupiter. This "classical" jovian is in a low-eccentricity orbit about 2 AU from its host G0-type star. Here is the ApJ paper by (Butler & Marcy 1996).
The second discovery of a jovian-mass planet orbiting very close (0.11 AU) to its primary star. Geoff Marcy also announced at the Workshop on Planetary Formation in the Binary Environment at Stoney Brook (June 16-18, 1996) that they believe a second jovian exists in this system with a mass of ~5 Jupiters in a 15-20 year orbit. These planets orbit the G8V star 55 Cancri A. Orbiting further out from A and its planets is an M5 dwarf (55 Cancri B) which lies ~1150 AU away.
From the Allegheny Observatory astrometric work done by George Gatewood and co., it appears that there are two "classical jovians" orbiting Lalande 21185. One has a period of about 30 years (1.6 jovian masses, a = 10 AU) and one with a period of 6 years (0.9 Jovian masses, a = 2.5 AU). These planets will hopefully hold up as the first confirmed astrometric detection of a planetary system. Other astrometry-based planet discoveries have come and gone (e.g. Van deKamps planets around Barnard's star in the 70's), will this one survive? There has been some debate over the authenticity of this discovery, primarily by researchers who have montiored Lal 21185 by Doppler spectroscopy. Lal 21185 is the 5th closest star to our Sun.
Tau Boo b was suspected to be a spectroscopic binary companion by Duquennoy and Mayor in 1991. The orbit was confirmed by Marcy & Butler and Mayor, Udry, & Queloz in 1996. Both groups announced their recent data at the 188th AAS meeting in Madison, in June 1996. The new doppler velocity curves indicate that "c" is most likely planetary in nature, according to its minimum mass (about 4 jovian masses). The object appears to orbit only 8 stellar radii from the F7V primary: Tau Boo A. The orbit has also been confirmed by a group using the AFOE with collaborators from the Harvard-Smithsonian Center for Astrophysics, the High Altitude Observatory, and Penn State University. Tau Boo A's other stellar companion, Tau Boo B, is an M2 dwarf which appears to be in an eccentric orbit around Tau Boo A and its planetary companion C. According to Hale (1994), B's orbital period around A+C is ~2000 years, with a = 245 AU, and e = 0.91.
The fourth "epistellar jovian" discovered, with mass (0.60 jovian masses), period (4.61 days), and orbital radius (0.054 AU) values that are nearly the same as 51 Peg b's. The primary is a F8V star about 16.5 pc away. The discovery was released as part of a poster paper authored by Hauser, Shirts, Williams, Butler, and Marcy at the ASP 1996 Conference "From Stardust to Planetesimals" in late June, 1996.
A spectroscopic companion to the solar-like star 16 Cyg B has been discovered independently by Cochran & Hatzes (Univ.of Texas) and Marcy & Butler (SFSU). The discovery announcement came at the 28th DPS meeting on October 23, 1996. This planet is a very notable discovery because it has the highest eccentricity of any known planet. The object appears to be a lower mass cousin of the "eccentric planets" 70 Vir b and HD 114762. The object has a minimum mass of 1.55 jovian masses and it orbits the G2.5V star 16 Cyg B in a period of 804 days (2.2 years). The other member of this system, 16 Cyg A, lies 900 AU away from B and C.
Rho Coronae Borealis
As the first announced extrasolar planet discovered by the AFOE/Whipple Observatory group, Rho CrB b has proved once again that Jupiter-mass planets may exist in close orbits to ordinary stars. The parent star, Rho CrB A is a ~10 billion year old analog of our sun (similar in mass and spectral type) lying roughly 55 light-years from our solar system. Its planetary companion has a minimum mass of 1.13 Jovian masses, and orbits the primary star once every 40 days at an orbital radius of about 0.25 AU; closer in than Mercury orbits in our own solar system. Four years of precise photometry by G. Henry shows that Rho CrB A is photometricly stable to within 0.00017 magnitude, effectively ruling out radial pulsations as the perturbation mechanism. The AFOE team previously confirmed Tau Boo Ab and 51 Peg b.