This is a painting for NASA of the formation of a distant solar system, used to illustrate the article “Formation of the Solar System: Birth of Worlds.”
It’s showing how clouds of dust and bits of solid matter – stuff that’s not blazing like stars – coalesce around a sun and gradually lump themselves into round, spinning blobs of matter – planets – and smaller, chunkier bits – asteroids and comets. It also shows how those big planets apparently move outward after forming closer to the star at the center of the system:
Our understanding of the solar system’s formation is also being guided by the new worlds discovered around distant stars. The unusual orbits of many of these distant planets have sparked a hot topic of research: that planets’ orbits may shift — migrate — early after their formation. This “planetary migration” is the best explanation for these newly discovered “hot Jupiters”– massive gas giants orbiting extremely close to their stars.
Planetary migration is caused by gravitational interactions between the gas in the solar nebula and the young planets, and also by gravitational interactions between the planets and the remaining planetesimals. These interactions transfer angular momentum between the objects, causing the planet too either give up energy, and move closer toward the star, or gain energy, and migrate outward.
One model for our own solar system suggests that our giant planets’ orbits shifted dramatically early in the solar system’s history, with Jupiter’s orbit migrating slightly inward toward the Sun, and those of Saturn, Neptune, and Uranus expanding farther from the Sun. These dramatic movements gave us the order of the planets and smaller bodies that we are familiar with today, and caused many smaller bodies (such as comets) to scatter out into the Kuiper belt and Oort cloud.