In 1995, astronomers discovered 51 Pegasi b, a gas giant orbiting its star closely, challenging existing theories of planet formation and demonstrating that planetary systems can have vastly different architectures than our own Solar System.
The discovery of 51 Pegasi b shattered the long-held belief that our Solar System was the only template for planetary organization, revealing the vast diversity of planetary systems across the galaxy and launching the modern era of exoplanet research.
The discovery of 51 Pegasi b in October 1995 by Swiss astronomers Michel Mayor and Didier Queloz marked a pivotal moment in astronomy, fundamentally altering the understanding of planetary systems. Prior to this finding, the Solar System served as the sole model for planetary organization, leading scientists to assume that other star systems would likely follow a similar pattern of large planets orbiting far from their stars and smaller rocky planets closer in.
51 Pegasi b, however, defied these expectations. It was identified as a gas giant, comparable in mass to Jupiter but orbiting its star at a distance much closer than Mercury orbits our Sun, completing a full revolution in just over four days. This characteristic earned it the classification of a 'hot Jupiter' and demonstrated that giant planets could form and exist in regions previously thought inhospitable. The detection was achieved not through direct observation, but by measuring subtle shifts in the star's motion caused by the planet's gravitational pull—a technique known as the radial velocity method. This groundbreaking discovery transformed exoplanet research from a speculative field into a burgeoning scientific discipline, spurring intensified searches that have since revealed thousands of diverse exoplanets and confirmed that planetary systems are far more varied than previously imagined.