PSR B1257+12 (sometimes abbreviated to PSR 1257+12) is a pulsar located 980 light-years from the Sun. As of 2007, three extrasolar planets have been discovered orbiting it. The first two were the first extrasolar planets ever discovered. Pulsar PSR B1257+12 is in the constellation of Virgo. The designation PSR B1257+12 refers to its coordinates in the B1950.0 epoch. It is located at about 980 light years from Earth. 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. It has a rotation period of 6.22 milliseconds (9,646.3rpm). Planets In 1992, Aleksander Wolszczan and Dale Frail discovered that the pulsar has two planets. These were the first extrasolar planets ever discovered [1]; as pulsar planets, they surprised many astronomers who expected to find planets only around main sequence stars. Additional uncertainty surrounded the system, because 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. he planets are believed to either be the rocky cores of former gas giants, or the result of a second round of planetary system formation resulting from unusual supernova remnants. It should be noted that the planets of PSR B1257+12 are designated from A to D (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.
PSR B1257+12 A
PSR B1257+12 A is the innermost planet orbiting the pulsar at a distance of 0.19 AU with an orbital period of approximately 25 days. In 1997, it was claimed that this planet was in fact an artifact caused by solar wind, but this claim has since been disproved. It is about twice as massive as Earth's Moon. PSR B1257+12 B
PSR B1257+12 B is the second planet orbiting the pulsar at a distance of 0.36 AU with an orbital period of approximately 66 days. The planet is over four times as massive as the Earth. Because planet B and planet C orbit rather close to each other, they cause measurable perturbations in each other's orbits. As expected, perturbations were detected confirming that the planets are real. Accurate masses of the two planets, as well as their inclinations, were measured by calculating how much the planets interfere each other. PSR B1257+12 C
PSR B1257+12 C is the third planet orbiting the pulsar at an average orbital distance of 0.46 AU with an orbital period of approximately 98 days. It is nearly four times as massive as the Earth.
Possible comet
It is suspected that an asteroid or comet is orbiting PSR B1257+12 at an average orbital distance of 2.6 AU with an orbital period of approximately 3.5 years. The object is so small that it is not even considered to be a planet, but it is the first known extrasolar asteroid or comet akin to the objects in the Kuiper belt in our solar system. It is possible that this object is the largest member of a belt of minor objects around the pulsar. It has an upper mass limit of 0.2 Plutos (0.0004 Earths) and a maximum diameter of 1000 km. However, this object is not yet confirmed. This object is sometimes referred to as PSR B1257+12 D Disproven gas giant In 1996, a possible Saturn-like (100 Earth mass) gas giant was announced orbiting the pulsar at a distance of about 40 AU. As the fourth planet in the system it was designated PSR B1257+12 D. However, the discovery was not conclusive and was later retracted. It is now thought that the signal came from an asteroidal or cometary body. See also * 51 Pegasi * PSR B1620-26 References 1 Pulsar Planets.
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