Which was the first exoplanet? 1992, 1995 and the 2019 Nobel Prize

Published 29 October 2026

21992: planets around a dead star

In a paper published in Nature on 9 January 1992, Aleksander Wolszczan and Dale Frail reported that the pulsar PSR B1257+12 is orbited by two or more bodies the size of planets. They had timed its pulses with the 305-metre Arecibo radio telescope. The two bodies they described have minimum masses of about 2.8 and 3.4 times the mass of the Earth and go round the pulsar in about 98 and 67 days.

A pulsar is what is left after a massive star has exploded: a small, dense, fast-spinning object that sweeps a beam of radio waves past the Earth with clock-like regularity – in this case once every 6.2 thousandths of a second. Planets around such an object were a complete surprise, and no one expected life there.

Wolszczan graduated in astronomy from the Nicolaus Copernicus University in Toruń in 1969 and works at Penn State University in the United States.

3How you find a planet with a clock

A pulsar’s pulses arrive at very regular intervals. If a planet orbits the pulsar, both move around their common centre of mass, so the pulsar is sometimes a little nearer to us and sometimes a little farther away. The pulses then arrive slightly early or slightly late, in a pattern that repeats with the planet’s orbit. Wolszczan and Frail found two such patterns overlapping, one for each planet.

41995: a planet around a star like the Sun

On 6 October 1995 Michel Mayor and Didier Queloz of the University of Geneva announced a planet orbiting 51 Pegasi, a star like the Sun about 45 light years away in the constellation Pegasus. Their paper in Nature was titled “A Jupiter-mass companion to a solar-type star”.

They had found it with a different method: not by timing pulses but by measuring the star’s light. Since April 1994 they had been following a sample of Sun-like stars with the ELODIE spectrograph at the Haute-Provence Observatory in France, which measured the motion of a star towards or away from us with an accuracy of about 13 metres per second. For 51 Pegasi the motion repeated every 4.23 days – the length of the planet’s year. How that works is explained in Discoveries.

The planet surprised everyone. It has at least about half the mass of Jupiter, yet it goes round its star in just over four days – far faster than Mercury, which needs 88 days to orbit the Sun.

5What the Nobel Prize recognised

The 2019 Nobel Prize in Physics was divided: one half went to James Peebles for theoretical discoveries in physical cosmology, the other half jointly to Michel Mayor and Didier Queloz “for the discovery of an exoplanet orbiting a solar-type star”.

The wording matters. The prize did not call 51 Pegasi b the first exoplanet; it recognised the first one found around a star like our own.

6Why both answers are right

If the question is “which planets outside the Solar System were found first?”, the answer is the planets of PSR B1257+12, in 1992. If it is “when did we first find a planet around a star like the Sun?”, the answer is 51 Pegasi b, in 1995.

The second discovery had the larger consequences. It showed that the method worked for ordinary stars and opened a systematic search for such planets that continues today – with Geneva instruments and missions such as HARPS and CHEOPS, described in Science.