Free Astronomy Magazine July-August 2026

13 ASTRO PUBLISHING called accretion. Dust gloms to- gether into pebbles, which collide and grow larger and larger, forming protoplanets and eventually planets. The largest then collect gas to be- come giants like Jupiter. Since it takes more time for gas giants to form, and the disk of planet-form- ing material eventually evaporates and disappears, planetary systems end up with many more small plan- ets than large planets. In contrast, stars form when a vast cloud of gas fragments and each piece collapses under its own gravity, growing smaller and denser. A similar frag- mentation process could theoreti- cally occur within protoplanetary disks as well. That could explain why some very massive objects are found billions of miles from their host stars, in regions where the protoplanetary disk should have been too tenuous for accretion to occur. 29 Cygni b sits on the dividing line between what can be explained by these two different mechanisms. It weighs 15 times Jupiter and orbits its star at an average distance of 1.5 billion miles (2.4 billion kilometers), about the same as Uranus in our solar system. The research team tar- geted it because it could potentially result from either process. “In computer models, it’s very easy for fragmentation in a disk to run JULY-AUGUST 2026