Which space telescope has discovered the most exoplanets up to the time described?

• A. Hubble
• B. Kepler
• C. Spitzer
• D. James Webb

Answer: (B)

The key idea is recognizing which telescope was built for hunting exoplanets with a large, continuous survey. Kepler did exactly that: it stared at about 150,000 stars in a fixed patch of sky and watched them for extended periods to catch tiny, regular dips in brightness as planets passed in front of their stars. This transit method, applied to so many stars over years, yielded thousands of planet candidates and far more confirmed exoplanets than any other telescope, making it the leader in discoveries of exoplanets up to that time. Other telescopes like Hubble and Spitzer contributed important exoplanet science, especially in studying atmospheres, but not on the same scale for discovering new planets. James Webb is exceptional for follow-up and detailed characterization, not the broad, all-sky hunt Kepler performed.