The planet, designated 51 Pegasi b, was a Jupiter-sized gas giant orbiting its star every 4.2 days. Its existence was not seen but inferred from a rhythmic wobble in the star’s light, a 50-meter-per-second tug measured with exquisite precision. The data revealed a world so close to its sun that its year was shorter than a week on Earth. Its surface temperature was estimated at 1,000 degrees Celsius. This was not the placid, distant solar system of textbooks. It was a furnace.
The discovery mattered because it ended a 2,400-year-old philosophical debate. Since the time of the Greek atomists, humans had speculated about other worlds. Mayor and Queloz provided the first concrete evidence. Their finding immediately validated the search, triggering an astronomical gold rush. Within a decade, the count of known exoplanets climbed from zero to hundreds. The field of comparative planetology, once confined to our own solar neighborhood, suddenly had a galaxy of subjects.
A common misunderstanding is that 51 Pegasi b was a potentially habitable, Earth-like world. It was the opposite. It was a 'hot Jupiter,' a type of planet theorists had not predicted could exist so close to a star. Its discovery forced a complete rewrite of planetary formation models. Scientists had to invent new theories of planetary migration to explain how a gas giant could spiral inward without falling into its star.
The lasting impact is a new cosmic census. The Kepler and TESS space telescopes, direct descendants of this discovery, have since cataloged thousands of exoplanets. We now know planets outnumber stars in the Milky Way. The question shifted from 'Are there other worlds?' to 'Which one will we study next?' The search for a true Earth analog, a pale blue dot around another sun, began in earnest on this date.