Exoplanet 29 Cygni b (Artist's Concept)

Exoplanet 29 Cygni b, seen in this artist’s concept, is a gas giant weighing about 15 times the mass of Jupiter. It orbits a type A star (shown at upper right) slightly hotter and more massive than our Sun, at an average distance of 2.4 billion kilometres. The star is known to possess a dusty debris disc. A hypothetical comet fragment is shown approaching the planet, while previous impacts have left dark splotches on its cloudtops, similar to what was seen from the Shoemaker-Levy 9 impact on Jupiter in our solar system.

Astronomers studied 29 Cygni b with Webb to determine that it likely formed from accretion, a bottom-up process where small bits of rock and ice clump together and grow larger over time, rather than from disc fragmentation. In other words, it formed like a planet and not like a star.