25 Years of Exoplanet Discoveries

Image Credit: NASA/JPL-Caltech 

January 9, 2017 is the 25th anniversary of the announcement of the first confirmed exoplanets. The planets were discovered around the pulsar PSR 1257+12 from the Arecibo Observatory by Alex Wolszczan and Dale Frail.

Note from the Discoverer

The pulsar planets have been detected orbiting PSR B1257+12, the 6.2-millisecond pulsar discovered in February 1990, during a survey of the radio sky with the 305-m Arecibo radio telescope. The two outer planets, announced in January 1992, have masses of about 4 times the mass of our Earth, and the inner one, detected in 1994, is only twice as massive as the Moon. The corresponding orbital periods of the three planets are 98, 65 and 25 days. The whole system is compact enough to fit inside the orbit of Mercury.

The pulsar planet discovery has been made using the highly precise pulse timing technique. It was possible because the orbiting planets make the pulsar wobble in space, and that motion translates into easily measurable, millisecond variations in the pulse arrival times at the telescope. The same technique was used to confirm the existence of the pulsar planets by detecting subtle changes in the orbits of the two larger planets caused by their proximity to the 3:2 orbital resonance.

A planetary system orbiting PSR B1257+12 represents the first confirmed planets beyond the Sun. It is also the first extrasolar planetary system, in which an orbital resonance has been measured, and it is the first example of a “tightly packed”, super-Earth mass system, which is the kind of orbital configuration now commonly detected by the Kepler telescope and the most sensitive radial velocity surveys. From the very start, the existence of such a system carried with it a prediction that planets around other stars must be common, and that they may exist in a wide variety of architectures, which would be impossible to anticipate on the basis of our knowledge of the Solar System alone.

- Alex Wolszczan

IAU Exoworlds

References

• • Discovery Paper: A planetary system around the millisecond pulsar PSR1257+12

  • Original Press Coverage: The New York Times

• Pulsar and Planets names from the IAU.

  • Review: Why Are Pulsar Planets Rare?

  • Review: Discovery of Pulsar Planets.

• More papers about pulsar planets from ADS.