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PSR B1257+12 d (ex PSR B1257+12 C) is an extrasolar planet approximately 980 light-years away in the constellation of Virgo (the Virgin). PSR B1257+12C was one of the first planets ever discovered outside the Solar system, and is currently the third object known to be orbiting the pulsar PSR B1257+12. The planet is nearly four times as massive as the Earth.
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 the other extrasolar planets is mainly because of the time of their discovery. Being the first ever 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 then the other two), the name "A" was commonly used. The name 51 Pegasi b (the first planet found around a Sun-like star) was the idea used for naming planets around regular stars.
- Wolszczan, A., Frail, D. (1992). "A planetary system around the millisecond pulsar PSR1257 + 12". Nature 355 (6356): 145–147. DOI:10.1038/355145a0.