PSR B1257+12, previous designation PSR 1257+12, is a pulsar located 2,300 light years away from the Sun. It is located in the constellation Virgo.

The pulsar contains a planetary system, with three known extrasolar planets. They are named "Draugr" (PSR B1257+12 A), "Poltergeist" (PSR B1257+12 B), and "Phobetor" (PSR B1257+12 C), respectively. They were both the first extrasolar planets discovered and they were also the first pulsar planets to be discovered. b and c were found in 1992, and a was found in 1994. a is the lowest mass planet yet discovered by any observational technique, with somewhat less than twice the mass of Earth's moon.



PSR B1257+12 was discovered by the Polish astronomer Aleksander Wolszczan on February 9, 1990 using the Arecibo radio telescope. It is a millisecond pulsar, a kind of neutron star, with a rotation period of 6.22 milliseconds (9,650 rpm), 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 pulsar is estimated to have a mass of 1.4 Solar masses, typical for most neutron stars and pulsars. The radius is also estimated to be around 10 kilometers (~0.000015 Solar radius), which is also typical for pulsars and neutron stars. The pulsar is extremely hot, with a surface temperature of either less than or equal to around 28856 K. The pulsar formed about one to three billion years ago as the result of a white dwarf transforming into a rapidly spinning neutron star during the process of two white dwarfs merging with each other.

The discovery stimulated a search for planets orbiting other pulsars, but it turned out such planets are very rare; only one other pulsar planet, orbiting PSR B1620-26, has been confirmed.

Planetary systemEdit

In 1992, Aleksander Wolszczan and Dale Frail discovered that the pulsar had two planets. This was the first discovery of an extrasolar planet. as pulsar planets, these planets surprised astronomers as they only expected to find planets orbiting 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 on, in 1994, an additional planet was discovered around the pulsar.

The planets are believed to be the result of a second round of planetary system formation, resulting from unusual supernova remnants or a quark nova.

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.

Planet Mass Semimajor axis Orbital period (days) Eccentricity Inclination Radius
A/Draugr 0.020 ± 0.002 Earth mass 0.19 AU 25.262 ± 0.003 days 0.0 ~50° N/A
B/Poltergeist 4.3 ± 0.2 Earth mass 0.36 AU 66.5419 ± 0.0001 days 0.0186 ± 0.0002 53° N/A
C/Phobetor 3.9 ± 0.2 Earth mass 0.46 AU 98.2114 ± 0.0002 days 0.0252 ± 0.0002 47° N/A