The discovery of the first planet orbiting a star outside our solar system, 51 Pegasi b, was announced in 1995. Astronomers using the radial velocity method, which relies on measuring the wobble of a star caused by the gravitational pull of an orbiting planet, confirmed the existence of 51 Pegasi b. Although astronomers have since found thousands of exoplanets, 51 Pegasi b remains a significant discovery because it ______ a new era in astronomy—the era of exoplanet discovery.

SAT · English · previous-year question