Hot, helpful Jupiters may spawn Poseidon planets
When astronomers started discovering so-called “hot Jupiters” in extrasolar systems, many thought the jig was up for life-bearing worlds there. Many of the 280+ star systems so far discovered have either hot Jupiters or hot Neptunes… gas giants or ice giants that have migrated since planetary formation into the interiors of their systems. It’s likely that random orbital interactions just after planet formation cause outer giants, in some cases, to spiral inward toward their stars and take up permanent residence at a close orbit… sometimes so close the gas giants almost graze their sun’s surface.
Considering how the inward migration of such giants would likely wreak havoc among inner terrestrial worlds, it was assumed generally among planetary scientists that such systems would be barren of life. As an object the size of Jupiter or Saturn moves inward, spiraling in response to some original perturbation in the outer system, it would tend to dislodge small, inner planets and send them hurtling into the void… or into their sun. Unless the Jupiter-in-motion carried its own icy moons, which could melt to form oceans if their giant settled into a stable orbit in its star’s habitable zone (HZ), life wouldn’t have much of a future in systems with a hot Jupiter.
Or maybe it would. Planetquest recently posted an article about the work of Sean Raymond, at the University of Colorado, who models the formation of planetary systems containing hot Jupiters. Using computer models that simulate the accretion of planets during solar nebula collapse, Raymond has spent some time exploring what happens when gas giants form in a system and then careen inward to stable orbits before their solar system matures. His work casts doubt on the prevailing wisdom that hot-Jupiter systems are by definition devoid of life.
According to Raymond’s work, when hot Jupiters swing inwards toward their star, some of the orbital disturbance resulting from their big move causes icy and rocky asteroid material to swarm inward, too. Pulled in thrall to the wandering giant, gigatons of ice and rock swish closer to their star and begin to congeal into a “second generation” of inner, rocky planets. With the rogue giant safely ensconced in a close orbit, its gravity is not longer a threat to planet formation further out, allowing Earths and Super-Earths to accrue within the HZ. According to Raymond’s calculations, such next-gen planets would be likely to have many times Earth’s complement of water and volatiles… meaning they would be ocean worlds. Raymond’s work is still in progress, and I look forward to seeing the published results of his work. If his calculations hold up to scrutiny, there may be far more potential for life out there than previously assumed… and Earths may not be so rare after all.