Generally speaking, exoplanets can be any size, and they are found in a wide range of orbits. Some have massive gas atmospheres; others are smaller with an icy or rocky composition.

In 1999, my team discovered that the star Upsilon Andromedae was circled by three gas-giant planets - the first distant multiplanet system ever found. That same year, other researchers observed the first 'transit' of an exoplanet - a planet blocking out a small fraction of the starlight as it passes in front of the star.

One of the first thoughts I had, when doing early exoplanet research, was that Earth and its many companions seemed very different from the planetary systems we were detecting.

Debra Fischer Quotes