1992

PSR B1257+12

Wolszczan and Frail announce planets around pulsar PSR 1257+12

The planets were found because their gravity made a dead star’s radio pulses arrive about three milliseconds early, then three milliseconds late.

9 January 1992

On 9 January 1992, Nature published Aleksander Wolszczan and Dale Frail's paper reporting that precision timing of the millisecond pulsar PSR 1257+12 showed it was orbited by two or more planet-sized bodies. A Cornell University press release publicised the result the same day.

The team inferred two companions with minimum masses of 3.4 and 2.8 Earth masses, orbital periods of 66.6 and 98.2 days, and orbital distances of 0.36 and 0.47 astronomical units.

Four thousand arrival times

The evidence was the periodic shift in when the pulsar's radio pulses reached Earth: the orbiting bodies made it move toward and away from us around the system's centre of mass. Arecibo's 305-metre dish recorded more than 4,000 pulse-arrival measurements from July 1990 to November 1991, from an object spinning about 162 times a second.

Timing residuals were dominated by 66- and 98-day cycles, and a two-planet reflex-motion model explained them after alternative pulsar, propagation and instrumental explanations were examined. The planets were inferred, not photographed.

Why “first confirmed” needs a footnote

The paper presented highly persuasive evidence, but the predicted mutual gravitational perturbations between the planets — the dynamical confirmation — had not been measured on 9 January. Within two weeks other astronomers proposed exactly that test, because the two periods lie close to a 3:2 ratio; Wolszczan's 1994 paper described the detection of those perturbations as irrefutable.

The host is a neutron-star remnant, not a main-sequence star; the first confirmed planet around a Sun-like star was 51 Pegasi b in 1995. A planet around Gamma Cephei had been reported in the late 1980s, rejected at the time, and confirmed only in 2003.

The 1992 paper securely modelled two companions and mentioned evidence for another; the system's additional inner, moon-mass planet was reported with the 1994 confirmation.

Sources

Researched 23 Aug 2026 7 sources 2 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at 1992-01-09.

What the sources leave uncertain

The 9 January 1992 publication and press-release date is secure.
The label 'first confirmed exoplanets' needs qualification. The 1992 paper announced the first broadly accepted planetary system beyond the Solar System, but Wolszczan's 1994 paper described the later detection of predicted mutual perturbations as the irrefutable dynamical confirmation.
A planet around Gamma Cephei had been reported in the late 1980s but was not accepted then; that earlier claim was confirmed in 2003. Thus 'first' changes depending on whether it means first convincing contemporary confirmation or earliest published claim eventually validated.
The 1992 paper securely modeled two Earth-mass companions and mentioned evidence for another. The system's additional inner, moon-mass planet was reported with the 1994 confirmation.