Super-puffs are extrasolar planets with masses only a few times larger than Earth’s, radii larger than Neptune, and very low densities.

First discovered by NASA’s Kepler space telescope, these planets are relatively rare in our Milky Way Galaxy — fewer than 15 have been discovered so far.

“Kepler-51’s trio take planetary puffiness to new levels,” said Dr. Zachory Berta-Thompson, an astronomer in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder.

“Their discovery was straight-up contrary to what we teach in undergraduate classrooms.”