For Centauri Dreams, the most exciting part of the exoplanet hunt is the refinement of our models. We know, for example, of numerous planetary systems dominated by gas giants. Now we’re trying to figure out which of these may contain smaller, rocky worlds, and that means learning more about solar system dynamics. A step in the right direction emerges from a June paper that analyzes what happens to moon-sized protoplanets as they evolve in systems with gas giants.

Based on computer simulations, the work assumes a giant planet the size of Jupiter and manipulates the position and mass of the protoplanets in these settings over time, testing four systems with known planets: 55 Cancri, HD 38529, HD 37124 and HD 74156. The most interesting result is the ready formation of terrestrial worlds around 55 Cancri, often with orbits in the habitable zone. HD 38529 also produced a rocky world, one about the size of Mars, and showed conditions favorable to an asteroid belt as well. No further planets evolved around HD 37124 and HD 74156.

“It’s exciting that our models show a habitable planet, a planet with mass, temperature and water content similar to Earth’s, could have formed in one of the first extrasolar multi-planet systems detected,” said Rory Barnes, a postdoctoral researcher at the University of Arizona who is a co-author of the study.

Exciting indeed. 55 Cancri, a G-class star in Cancer 41 light years from Earth, is already thought to be orbited by as many as four planets. Learning more about such systems will help us refine the target list for planet hunting space missions like New Worlds Imager. Remarkably, we may be no more than a decade or so away from being able to see such planets, and transit methods may snare a terrestrial world sooner still.

The paper is Raymond, Barnes and Kaib, “Predicting Planets in Known Extrasolar Planetary Systems. III. Forming Terrestrial Planets,” Astrophysical Journal 644, pp. 1223-1231, with abstract here.