PSR B1257+12 is in the constellation Virgo. The designation "PSR B1257+12" refers to its coordinates in the B1950.0 epoch and it being a pulsar.
- Mass: 0.020 ± 0.002 Earth mass
- Semimajor axis: 0.19 AU
- Orbital period: 25.262 ± 0.003 days
- Eccentricity: 0.0
- Inclination: ~50°
- Mass: 4.3 ± 0.2 Earth mass
- Semimajor axis: 0.36 AU
- Orbital period: 66.5419 ± 0.0001 days
- Eccentricity: 0.0186 ± 0.0002
- Inclination: 53°
- Mass: 3.9 ± 0.2 Earth mass
- Semimajor axis: 0.46 AU
- Orbital period: 98.2114 ± 0.0002 days
- Eccentricity: 0.0252 ± 0.0002
- Inclination: 47°
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.