PSR B1257+12 A

PSR B1257+12 b, alternatively designated PSR B1257+12 A, also named Draugr, is an extrasolar planet approximately 2,300 light-years (710 pc) away[4] in the constellation of Virgo. The planet is the innermost object orbiting the pulsar PSR B1257+12, making it 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 (with the mass accurately determined) known, including among the planets in the Solar System.[1]

PSR B1257+12 b
Exoplanet Comparison PSR B1257+12 A.png
Size comparison of PSR B1257+12 b with Earth.
(Based on selected hypothetical modeled compositions)
Discovered by
Discovery site United States[1]
Discovery date22 April 1994
Pulsar timing
Orbital characteristics
0.19 AU (28,000,000 km)[2]
25.262 ± 0.003[2] d
Inclination50[2][note 1]
2,449,765.6 ± 0.2[2]
StarPSR B1257+12
Physical characteristics
Mass0.020 ± 0.002[2][note 1] MEarth
Temperature266 K (−7 °C; 19 °F)[3]
  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.


The convention that arose for designating pulsars was that of using the letters PSR (Pulsating Source of Radio) followed by the pulsar's right ascension and degrees of declination. The modern convention prefixes the older numbers with a B meaning the coordinates are for the 1950.0 epoch. All new pulsars have a J indicating 2000.0 coordinates and also have declination including minutes. Pulsars that were discovered before 1993 tend to retain their B names rather than use their J names, but all pulsars have a J name that provides more precise coordinates of its location in the sky.[5]

On its discovery, the planet was designated PSR 1257+12 A and later PSR B1257+12 A. It was discovered before the convention that extrasolar planets receive designations consisting of the star's name followed by lower-case Roman letters starting from "b" was established.[6] However, it is listed under the latter convention on astronomical databases such as SIMBAD and the Extrasolar Planets Encyclopedia. Hence the designation PSR B1257+12 b.

In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[7] The process involved public nomination and voting for the new names.[8] In December 2015, the IAU announced the winning name was Draugr for this planet.[9][10] The winning name was submitted by the Planetarium Südtirol Alto Adige in Karneid, Italy. Draugr are undead creatures in Norse mythology.[11]


  1. ^ a b Dumé, Belle (11 February 2005). "Astronomers find smallest exoplanet". PhysicsWeb. Retrieved 20 July 2012.
  2. ^ a b c d e f Konacki, M.; Wolszczan, A. (2003). "Masses and Orbital Inclinations of Planets in the PSR B1257+12 System". The Astrophysical Journal. 591 (2): L147–L150. arXiv:astro-ph/0305536. Bibcode:2003ApJ...591L.147K. doi:10.1086/377093.
  3. ^ Extrasolar Visions - PSR 1257+12 A Archived December 26, 2010, at the Wayback Machine
  4. ^ Yan, Zhen; et al. (2013). "Very long baseline interferometry astrometry of PSR B1257+12, a pulsar with a planetary system". Monthly Notices of the Royal Astronomical Society. 433 (1): 162–169. Bibcode:2013MNRAS.433..162Y. doi:10.1093/mnras/stt712.
  5. ^ Lyne, Andrew G.; Graham-Smith, Francis. Pulsar Astronomy. Cambridge University Press, 1998.
  6. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  7. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  8. ^ NameExoWorlds The Process
  9. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  10. ^ The Proposals page for Mu Arae Archived 2017-04-05 at the Wayback Machine, International Astronomical Union, 2016-01-03.
  11. ^ NameExoWorlds The Approved Names

External linksEdit

Preceded by Least massive known exoplanet
Succeeded by

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