Exoplanet hunters disagree over who made the first discovery of a world orbiting another star. The question can even inspire a bit of intercontinental rivalry, with both American and European teams laying claim to “firsts.”

The very first planetary bodies outside our solar system to be clearly identified orbit a bizarre object called a pulsar. This is the extremely dense, rapidly spinning core of a star that has died a spectacular death: blowing itself apart in a supernova explosion. Pulsars shoot intense beams of radio waves in opposite directions as they spin, like rapidly rotating lighthouse beacons. This characteristic came in handy during early attempts to locate planets circling other stars.

By measuring changes in the pulsing beat from just such a spinning, stellar corpse, Dr. Alexander Wolszczan of Pennsylvania State University found three “pulsar planets.” The planets’ gravitational tugs altered the rhythm of the pulsar, revealing their existence by a kind of interstellar Morse code.

Wolszczan announced the discovery of two in 1992, confirming the third two years later.

Many scientists, however, say the strange circumstances that give rise to pulsar planets—not to mention the extreme environment of destructive radiation around a pulsar—make them radically different from planets orbiting still-living stars.

For the first exoplanet detection in that category, the prize goes to a Swiss team led by Michel Mayor and Didier Queloz, who announced their discovery of 51 Pegasi b on October 6, 1995. This is widely acknowledged as the first true exoplanet to be identified in orbit around a normal star, a scientific milestone that proved worthy of a 20th anniversary celebration.

PLANET TYPE
Terrestrial
DISCOVERY DATE
1994
MASS
0.02 Earths
PLANET RADIUS
Unknown
ORBITAL RADIUS
0.19 AU
ORBITAL PERIOD
25.3 days
ECCENTRICITY
0.0
DETECTION METHOD
Pulsar Timing