A new set of simulations shows that systems with so-called "hot Jupiters" might also have mini-Oort clouds detectable by today's space telescopes, giving astronomers a new potential tool for finding exotic extrasolar systems.
A newborn stellar system is a messy place. Infant planets compete to accrete gas and material, gobbling up anything that comes close. Sometimes these newly formed planets will pass near each other, gravitationally ricocheting into a new orbital configuration. Today’s space telescopes could detect the clouds of icy bodies produced by these close encounters, pointing observers to certain types of planetary systems.A new study by Sean Raymond (Universitè de Bordeaux) and Phillip Armitage (University of Colorado) examined the effects of planet interactions on the remaning planetesimals in simulated solar systems. Each simulation started with 3 gas giants and a disk of smaller bodies. Raymond and Armitage tracked the interactions over time, measuring the position and velocity of every object in the simulation. They chose a variety of initial masses and locations for their planets and ran thousands of simulations. They found that for a small fraction of systems, a cloud of small bodies would form about 100 to 1,000 times farther away from the central star than Earth’s distance from the Sun.
These clouds are 1,000 times smaller than the solar system’s Oort Cloud, the flock of small bodies thought to be our source of long-period comets. Nevertheless, the mini-Oort clouds share many Oort Cloud characteristics: they're roughly sphere-shaped (rather than contained in a disk) and the individual objects take a long time to complete their highly elliptical orbits. Their origin is similar to the Oort Cloud’s too. When gas giants graze the planetesimal disk, the ensuing gravitational mosh pit adds energy to the planetesimals, flinging them to more elliptical and inclined orbits. Some of the objects are ejected from the system completely.
In most of the simulations, only one gas giant remains while the other two are completely ejected. The surviving giant migrates inward, becoming a “hot Jupiter,” scorchingly close the central star. With the gas giants out of the picture, the planetesimals settle into new orbits quite different from their original trajectories.
The interaction between planetesimals in their new orbits would produce dust that would be visible with the Spitzer and Herschel Space Telescopes. If Raymond and Armitage are correct, then the presence of hot Jupiters and mini-Oort clouds would be correlated. It is now up to observers to test this prediction and see if the gravitational madhouse that is a newborn solar system really does produce comets and mini-Oort clouds around other stars.