Dale Frail and Aleksander Wolszczan reported planetary companions to a millisecond pulsar in 1992. Their evidence came from small periodic variations in the arrival times of its radio pulses.
An orbiting pulsar changes its Euclidean distance from the observer, changing the travel time of its radio waves. Timing residuals can therefore reveal a reflex orbit and constrain unseen companion masses. This method found a planetary system around a neutron star, a very different environment from the Solar system.[ref]
A planetary system around the millisecond pulsar PSR1257 + 12 by Aleksander Wolszczan and Dale Frail. pp. 145–147: timing variations and planetary interpretation
Portrait of Dale Frail
. Dale Frail. CC BY 3.0, via Wikimedia Commons. Source.
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