Astronomers would go on to take spectra of scores of exoplanets, but HD 209458 b’s brightness, size, and proximity to Earth made it a prime target, especially in the first heady days when scientists were proving they could not merely find planets, but study and characterize them as well.
The modern era
In 2009, the Kepler Space Telescope launched, and the trickle of planets became a deluge. Kepler, staring at tens of thousands of stars and watching for transits, delivered hundreds of planet candidates, then thousands, within only a few years. Astronomers didn’t have to examine planets one by one any longer, but could perform population studies, comparing these worlds in large numbers.
Of course, Kepler had its problems, too. Stars are more variable than scientists expected, and exoplanets harder to find. But Kepler taught astronomers more about stellar activity than decades of previous studies. Kepler also ran into mechanical difficulties, but astronomers learned to work with and around the telescope’s troublesome reaction wheels to steer it to new findings and new missions. They innovated, adapted, and overcame.