Epoch J2000.0 Equinox J2000.0
|Declination||+12° 40' 57"|
|Spectral type||neutron star|
|Mass||assumed 1.5 M☉|
|Age||3 × 109  years|
PSR J1300+1240 , PSR B1257+12 , PSR 1257+12 , PSR 1300+1240
PSR B1257+12 was discovered by the Polish astronomer Aleksander Wolszczan in 1990 using the Arecibo radio telescope. It is a millisecond pulsar, a kind of neutron star, and was found to have anomalies in the pulsation period, which led to investigations as to the cause of the irregular pulses. In 1992 Wolszczan and Dale Frail published a famous paper on the first confirmed discovery of planets outside our solar system. Using refined methods one more planet was found orbiting this pulsar in 1994. The discovery stimulated a search for planets orbiting other pulsars, but it turned out such planets are rare; only one other pulsar planet, orbiting PSR B1620-26, has been confirmed. PSR B1257+12 has a rotation period of 6.22 milliseconds (9,650 rpm).
Planetary system 
(in order from star)
|A (b)||0.020 ± 0.002 M⊕||0.19||25.262 ± 0.003||0.0||—||—|
|B (c)||4.3 ± 0.2 M⊕||0.36||66.5419 ± 0.0001||0.0186 ± 0.0002||—||—|
|C (d)||3.9 ± 0.2 M⊕||0.46||98.2114 ± 0.0002||0.0252 ± 0.0002||—||—|
In 1992, Aleksander Wolszczan and Dale Frail discovered that the pulsar has two planets. These were the first extrasolar planets ever to be confirmed; as pulsar planets, they surprised many astronomers who expected to find planets only around main-sequence stars. Additional uncertainty surrounded the system, because of a claim of an earlier pulsar planet around PSR 1829-10 that had to be retracted due to errors in calculations. Later, an additional planet was discovered. Additionally, this system may have an asteroid belt or a Kuiper belt.
The planets of PSR B1257+12 are designated from A to C (ordered by increasing distance), unlike planets around normal stars which follow the standard where the first discovered planet in the system is b, followed by c and so on.
Suspected fourth orbital body 
In 1996, a possible Saturn-like (100 Earth mass) gas giant was announced orbiting the pulsar at a distance of about 40 AU. The original hypothesis was retracted and a reinterpretation of the data led to a new hypothesis of a dwarf planet one-fifth the size of Pluto orbiting PSR B1257+12 at an average orbital distance of 2.4 AU with an orbital period of approximately 4.6 years. The dwarf planet hypothesis was also retracted because further observations showed that the pulsation anomalies previously thought to reveal a fourth orbital body are "not periodic and can be fully explained in terms of slow changes in the pulsar’s dispersion measure."
See also 
- 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.
- "Pulsar Planets".
- Wolszczan, A., Frail, D. (1992). "A planetary system around the millisecond pulsar PSR1257 + 12". Nature 355 (6356): 145–147. Bibcode:1992Natur.355..145W. doi:10.1038/355145a0.
- Podsiadlowski, P. (1993). "Planet Formation Scenarios". Planets around pulsars; Proceedings of the Conference, California Inst. of Technology, Pasadena, Apr. 30-May 1, 1992: 149–165. Bibcode:1993ASPC...36..149P.
- Planets orbiting Quark Nova compact remnants. arXiv:astro-ph/0301574. Bibcode:2003A&A...407L..51K. doi:10.1051/0004-6361:20030957.
- Wolszczan, Alex (1997). "The Pulsar Planets Update". Planets Beyond the Solar System and the Next Generation of Space Missions. Proceedings of a workshop held at Space Telescope Science Institute, Baltimore, MD, October 16-18, 1996. ASP Conference Series, Vol. 119. Astronomical Society of the Pacific. p. 135. Retrieved 02.03.2013.
- Fischer, Daniel (25.10.2002). "A comet orbiting a pulsar?". The Cosmic Mirror (244). Retrieved 02.03.2013.
- "Smallest extra-solar planet found". BBC News. 14.02.2005. Retrieved 02.03.2013.
- Wolszczan, Alex (January 2012). "Discovery of pulsar planets". New Astronomy Reviews (Elsevier) 56 (1): 2–8. doi:10.1016/j.newar.2011.06.002.
- Wolszczan, A. (1994). "Confirmation of Earth Mass Planets Orbiting the Millisecond Pulsar PSR B1257+12" (pdf). Science 264 (5158): 538–542. Bibcode:1994Sci...264..538W. doi:10.1126/science.264.5158.538. PMID 17732735.
- Wolszczan, A. et al. (2000). "Timing Observations of Four Millisecond Pulsars with the Arecibo and Effelsberg Radio Telescopes". The Astrophysical Journal 528 (2): 907–912. Bibcode:2000ApJ...528..907W. doi:10.1086/308206.
- Salter, C. (2001). "Radio Astronomy Highlights" (PDF). Arecibo Newsletter (33). Retrieved 2009-06-23.
- "Scientists announce smallest extra-solar planet yet discovered" (Press release). Pennsylvania State University. 2005.
- Pulsar Planets
- PSR 1257+12 on The Extrasolar Planets Encyclopaedia
- Britt, Robert Roy (29 May 2003). "A World With Two Suns". SPACE.com. Retrieved 2008-06-06.