Thirteen Extrasolar Planets


We may have lost Pluto, but there are plenty of other planets in the universe worthy of holding our attention. Granted, these new kids on the block are outside of our solar system.

Left, the sunlit side of 51 Pegasi b, the first planet ever detected around a sun-like star. Image source: Extrasolar Visions.

(1) Gliese 581 d: About 20 light years from Earth, this is the third planet of the red dwarf star Gliese 581. Gliese 581 d is the only terrestrial exoplanet discovered that orbits close to the habitable zone of its star. This zone is sometimes called the “Goldilocks Zone” because it is neither too hot or too cold on the planet’s surface. Technically, Gliese 581 d resides outside this “Goldilocks Zone”, but the greenhouse effect may offset the tendency toward being too cold and create enough heat to support liquid water.

(2) 16 Cygni B b: This water cloud Jovian planet has a very eccentric orbit, which means the surface of the planet experiences extreme differences in temperature throughout its year. Just over every two years, the planet’s orbit swings from a Venus-like distance of 0.6 AUs to a distance of 2.7 AUs, further than Mars.

(3) Epsilon Eridani b: At 10 light years away, Epsilon Eridani b is the closest confirmed planet to our solar system. Because of its close proximity, Eridanus shows up in Science Fiction often, such as in Isaac Asimov’s Foundation’s Edge and Robots and Empires; Greg Bear’s Eon; and C. J. Cherryh’s Alliance-Union Universe.

(4) Lalande 21185 b: This unconfirmed planet is thought to orbit a red dwarf star approximately eight light-years away in the constellation Ursa Major. The fourth closest star to our solar system, Lalande is a variable flare star that periodically increases in brightness. Lalande 21185 b may lie just over 2 times the Earth-Sun distance (AU) to its star, may be about nine tenths of Jupiter’s mass, and likely has an atmosphere of mostly hydrogen and helium.

(5) 51 Pegasi b: This was the first planet discovered orbiting another sun-like star. 51 Pegasi b is a massive Jupiter-like planet orbiting at a distance far closer than Mercury, a distance thought to be impossible for its size at the time of discovery. Its sun-like star is large enough to be visible from Earth by the naked eye under dark sky conditions. Unofficially named Bellerophon, this gas giant’s atmosphere is thick enough not to be blown away by solar wind despite its close proximity.

(6) PSR 1257+12 A: One of the first exoplanets ever discovered, this planet is over 908 light years away in the constellation Virgo. PSR 1257+12 A has a mass similar to that of the moon, and long ago its volcanism and tectonics subsided. Probably heavily cratered, it likely is comprised mostly of heavy elements, like iron.

(7) Tau Boötis b: About 50 light years away, this planet is the hottest known exoplanet. It is so hot that it may have silicate clouds and it may be visibly red. Tau Boötis b orbits its star in a “torch orbit,” that is at a distance from less than one seventh that of Mercury’s from the Sun.

(8) 55 Cancri b: This planet orbits its start every 14.65 days and was the fourth known extrasolar planet. 55 Cancri b was discovered by detecting variations in its star’s radial velocity caused by the planet’s gravity.

(9) Upsilon Andromedae b: This planet is a “hot Jupiter” type, meaning that it is extremely hot due to proximity to its star, so hot that it may glow red and its heat prevents water clouds from forming. Occasionally referred to as Upsilon Andromedae Ab to distinguish it from the red dwarf star Upsilon Andromedae B, it is about 44 light-years away in the constellation of Andromeda.

(10) Iota Draconis b: This planet is the “first object of planetary size detected around a red giant star.” Located about 100 light years from Earth, Iota Draconis b is over 8 times the mass of Jupiter, but may in fact be a brown dwarf star.

(11) 79 Ceti b: This planet was one of the first planets of sub-Saturn mass to be discovered around sun-like stars. Over 100 light years from Earth, 79 Ceti b orbits its star every 75 days. At potentially 111 times the mass of Jupiter, the planet may in fact be a very dim brown dwarf star.

(12) HD 209458 b: Unofficially also known as Osiris, this planet orbits the Solar twin star HD 209458 in the constellation Pegasus, 150 light-years from Earth. With the Hubble Space Telescope, scientists have detected sodium in the planet’s atmosphere.

(13) Rho Indi b: This planet is a water cloud Jovian type whose axis places Rho Indi b just outside the habitable zone. At over twice the mass of Jupiter, this planet orbits its star every 3.7 years.

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For more on exoplanets:
Space Topics: Extrasolar Planets
Physics World Extrasolar planets
The Planetary Society