Was Jupiter born beyond the current orbits of Neptune and Pluto?

Abstract

Ancient people named the planet Jupiter well. Both its brilliance and its slow, regal movement across the sky evoked a king among gods. Today we know much more about the influence of Jupiter, a planet boasting more than twice as much mass as the solar system’s other planets put together. Jupiter’s tremendous gravity stunted the growth of newborn Mars, sculpts the asteroid belt today, and may even help protect Earth from catastrophic comet impacts. A new theory suggests that Jupiter formed its core far from the Sun, then moved inward. Image credit: Hubble Space Telescope – NASA, ESA, and Amy Simon (NASA Goddard). But how did such a behemoth arise? Conventional theory says that Jupiter formed more or less where it is now, about five times farther from the Sun than Earth is. At that distance, the disk of gas and dust that swirled around the young Sun was dense enough to give birth to the planetary goliath. In 2019, however, two groups of researchers unaware of each other’s work—one in America (1), the other in Europe (2)—proposed a literally far-out alternative: Jupiter got its start in the solar system’s hinterlands, probably beyond the current orbits of Neptune and Pluto, and then moved inward. “It’s the most fun I’ve had with a paper for some time,” says Karin Oberg, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, and one of the theory’s originators. “You can explain it to almost anyone in a couple of minutes.” The theory may be straightforward, but its consequences are profound: If it’s right, the solar system’s biggest planet was born some 10 times farther from the Sun than it now is, which means that some of the other giant worlds in our solar system and beyond likely arose at vast distances from …