PSR B1257+12 A

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PSR B1257+12 b
Exoplanet List of exoplanets
Exoplanet Comparison PSR B1257+12 A.png
Size comparison of PSR B1257+12 A with Earth.
(Based on selected hypothetical modeled compositions)
Parent star
Star PSR B1257+12
Constellation Virgo
Right ascension (α) 13h 00m 01s
Declination (δ) +12° 40′ 57″
Distance 980 ly
(300 pc)
Spectral type Pulsar
Mass (m) assumed 1.4 M
Radius (r) ~0.00002 R
Age 0.8 Gyr
Orbital elements
Semi-major axis (a) 0.19[1] AU
Eccentricity (e) 0.0[1]
Orbital period (P) 25.262 ± 0.003[1] d
Inclination (i) 50[1][note 1]°
Time of periastron (T0) 2,449,765.6 ± 0.2[1] JD
Physical characteristics
Mass (m) 0.020 ± 0.002[1][note 1] M
Discovery information
Discovery date 22 April 1994
Discoverer(s) Aleksander Wolszczan
Maciej Konacki
Discovery method Pulsar Timing
Discovery site  United States[2]
Discovery status Published
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

PSR B1257+12 b (ex PSR B1257+12 A) is an exoplanet (or extrasolar planet) approximately 980 light-years away in the constellation of Virgo. The planet is the innermost object orbiting the pulsar PSR B1257+12, i.e. a pulsar planet in the dead stellar system. It is about twice as massive as the Moon, and is listed as the least massive planet known, including among the planets in the Solar System.[2]


The planets of PSR B1257+12 are designated from A to D (ordered by increasing distance). The reason that these planets are not named the same as other extrasolar planets is mainly because of time. Being the first extrasolar planets discovered, and being discovered around a pulsar, the planets were given the uppercase letters "B" and "C" (like other planets). When a third planet was discovered around the system (in a closer orbit than the other two), the name "A" was commonly used. The extrasolar planet name 51 Pegasi b (the first planet found around a Sun-like star), was the idea used for naming planets. Although these pulsar planets were not officially renamed, some have done it themselves. PSR B1257+12 A is catalogued as "PSR 1257+12 b" on The Extrasolar Planets Encyclopaedia.

The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[3][4] The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.[5]


  1. ^ a b The value of the inclination is assumed to be 50° based on the inclinations of the other two planets in the system, which have inclinations of 53° and 47° respectively. The quoted mass value is based on this assumed inclination.


External links[edit]

Media related to PSR B1257+12 A at Wikimedia Commons

Preceded by
PSR B1257+12 C
Least massive exoplanet
1994 —
Succeeded by

Coordinates: Sky map 13h 00m 01s, +12° 40′ 57″