April 22 – PSR B1257 12A

Extra-solar planet PSR B1257+12A was discovered on April 22nd 1994 by Aleksander Wolszczan and Maciej Konacki.

As exoplanets go it’s quite small.  Somehow it has been determined that this 500 parsec distant object that nobody can see is just twice the size of the Moon.  Only Kepler-37b (slightly better name) is smaller, while at the same time still managing to retain the description “planet”.  If it were much smaller it would probably not be called a planet.  The “PSR” in the same lets you know that this planet is orbiting a pulsar, a rotating neutron star, formed during the collapse of a massive star during a supernova.  This particular pulsar has a rotation period measured at a staggering 6.22 milliseconds, which, for the older readers among you, is 123 times faster than a 78rpm record player.

Three planets have so far been discovered around pulsar PSR 1257+12 by the Arecibo telescope in Puerto Rico.  All three have tight orbits, and would fit within the orbit of Mercury.  They were the first extra-solar planets to be discovered, with “B” and “C” being found first, followed by a third which, because it was closer to the star, became “A”.

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