(planet not in the solar system)
An extra-solar planet (or exoplanet) is a
planet outside the solar system, e.g.,
orbiting another star.
The first confirmed detection of
an exoplanet was in 1992 (PSR 1257+12 A) and the
first around a main sequence star
(51 Pegasi) in 1995.
As of 5/2021, 4300+ planets around 3200+ stars are known.
A number of methods have been contemplated for future technology:
- detecting the effects of magnetism, e.g., the planet's magnetic field's effect on the star's field.
The RV method reveals the relative masses of the host star and planet,
and a transit reveals their relative radius, so the density of
a planet can be estimated if the planet can be observed by both
methods, limited by the accuracy of these estimates for the star.
For this reason, follow-ups are carried out to detect it by both if that
possibility looks promising, leading to attempts to predict
transit times from RV data, especially if the orbit is long
(i.e., transits are infrequent) and available telescope time
Some terms used to indicate planets of various characteristics,
particularly their rough size:
- Earth analogs - roughly the size of Earth, rocky.
- super-Earths - noticeably larger than Earth, often confined to rocky planets.
- mega-Earths - term sometimes used for the largest super-Earths, e.g., more than 10 times the mass of Earth, yet rocky.
- mini-Neptunes - somewhat smaller than Neptune, sometimes confined to ice giants.
- Neptunes - roughly the size of Neptune, gas.
- gas giants - gas planet roughly Saturn size or larger.
- giant planets or extrasolar giant planets (EGPs), similar.
- Jupiters - roughly the size of Jupiter, gas.
- super Jupiters or super giants - into the brown-dwarf mass range, if considered a planet for other reasons.
- hot Jupiters - Jupiter-like, in tight orbits around the star, e.g., a fraction of a day, thus close to the star and very hot.
- hot Neptunes - similar for Neptune-sized planets.
Terms like super Neptune are also used to indicate a Neptune-like
When a rough classification based purely on mass is used,
brown dwarfs would be the next step up from planets, a
threshold being bodies of more than 13 Jupiter masses.
However sometimes other star- or planet-like characteristics are
taken as more important than the mass criteria.
(These terms present a writing style issue: whether Jupiter,
Earth, and Neptune should be capitalized, e.g., in hot Jupiter
or in Jupiters. I find no rules, and only partial consistency,
and have elected to follow the style I find most common.)
The spacecraft Kepler surveyed
a portion of the sky for exoplanets,
detecting (including K2) 5500 not-yet-eliminated candidates,
of which 2700 have been confirmed to be planets as of 12/2019.
Since Kepler, another mission, TESS has produced at least
Projected rough demographics based upon surveys:
- Half of star systems have super Earths.
- 1/6 have Earths.
- 5% have gas giants.
- 1% have hot Jupiters.
The commonly-used designation of exoplanets is somewhat-modeled
after the system for individual members of binary stars. The
first planet discovered is specified by the star's name followed
by "b", the next, "c". For example HD 80606 b is a planet
orbiting the star HD 80606.
If two or more are discovered simultaneously,
they are lettered outward from the innermost.
Referenced by pages:
Alpha Centauri (α Centauri)
adaptive optics (AO)
Automated Planet Finder (APF)
atmospheric temperature profile
AU Microscopii (AU Mic)
Black Widow Pulsar (B1957+20)
Beta Pictoris b (β Pic b)
bulk silicate earth (BSE)
candidate companion (CC)
CfA digital speedometer
California-Kepler Survey (CKS)
carbon dioxide (CO2)
color-color diagram (CCD)
core accretion model
Carl Sagan Institute (CSI)
double-line spectroscopic binary (SB2)
exoplanet eclipse light curve
equilibrium temperature (Teq)
European Southern Observatory Very Large Telescope (ESO VLT)
extreme adaptive optics (ExAO)
F-type star (F)
51 Eridani b
51 Pegasi b (51 Peg b)
47 Tucanae (47 Tuc)
general circulation model (GCM)
giant planet formation
Gliese-Jahreiss Catalog (GJ)
GJ 1132 b
GJ 1214 b
Gliese 436 b (GJ 436 b)
Gemini Planet Imager (GPI)
gravitational instability model
helium 1083 nm line
hot Jupiter (HJ)
internal gravity wave
intertropical convergence zone (ITCZ)
K-type star (K)
Keck Planet Finder (KPF)
Keck Planet Imager and Characterizer (KPIC)
Laplace-Lagrange secular theory
Lyot coronagraph (CLC)
maximum iron fraction
minimum mass (m sin i)
natural astronomical telescopes
New Worlds Mission
numerical weather prediction (NWP)
Open Exoplanet Catalogue (OEC)
one dimensional climate model
Origins Space Telescope (OST)
Other Worlds Laboratory (OWL)
projected semi-major axis
Qatar Exoplanet Survey (QES)
radial velocity (RV)
rare designator prefixes
Rossiter-McLaughlin effect (RM effect)
radial velocity method
Sloan Digital Sky Survey (SDSS)
spectroscopic binary (SB)
stellar radius determination
Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS)
Transiting Exoplanet Survey Satellite (TESS)
Tucana Horologium association (THA)
TOI 700 d
Terrestrial Planet Finder (TPF)
Trans-Atlantic Exoplanet Survey (TrES)
transit timing variations (TTV)
TW Hydrae (TW Hya)
Ultimate Spitzer Phase Curve Survey (USPCS)
vegetation red edge (VRE)
water vapor planet
James Webb Space Telescope (JWST)
Roman Space Telescope (RST)