One of the things we constantly hope to find as we scour the universe with telescopes is a solar system that looks like ours. At this point in our technology, we can’t see worlds like Mercury, and I suspect Mars-like planets are beyond our capabilities too, as are outer worlds. Basically, we really want to see a twin of our solar system, but we don’t have the ability. We don’t know if our kind of a solar system is common or rare, and at this point, we can’t know it. We are finding pieces of our solar system reflected in other systems, however. We see Oort clouds and Kuiper Belts. One earth-like world has been found orbiting a Sun-like star. Each of these pieces helps confirm that what we see around us isn’t unique. These confirmations also help us see our models for our solar system’s evolution in context. We weren’t around to see how our solar system formed. We can’t look back in time to observe our past. All we can do is look for solar systems like ours that are doing things we think our solar system did.

One of the more fantastic parts of our solar system’s evolution is a theoretical time when the planets Jupiter and Saturn orbited the Sun in resonance, with Saturn orbiting twice for Jupiter’s once. The combined gravitational tugs of the worlds aligning over and over and over are thought to have sent myriad objects, including Neptune and Uranus, into wild new orbits, while triggering the great heavy bombardment of asteroids into every rock surface. This model, called the Nice model for the city where a group of planetary scientists worked out these ideas, does a solid job explaining our observed solar system, but we can’t test it except through computer simulations. 

Now, however, we have finally spotted one solar system with worlds in resonance, and we can see the orbits changing and the pulls this creates. While this isn’t proof that our solar system had this kind of resonance, it is evidence that this isn’t an uncommon situation.

The system WASP-148 has two close-in planets, orbiting in a one-to-four resonance, with the inner world orbiting every nine days, while the outer takes about 36 days. In a new paper in the journal Astronomy & Astrophysics, a team lead by Guillaume Hébrard has described how these worlds don’t orbit at the normal rates we see in isolated worlds. To simplify things, if these worlds orbited in perfect circles, we would see them move at constant rates. Instead, the worlds race to line up and linger together in their passages. These effects can be seen in radial velocity measurements. This is the first time this kind of an orbital dance has been seen on exoplanets, and it is a cool bit of science, showing us that these kinds of things do happen, and could have happened here.

This also implies that if there is a lot of debris to be flung around in that solar system, the worlds we’re looking at likely see their skies often lit up with the light of incoming asteroids and comets. So while this discovery is cool, I don’t think we should visit.  

More Information

CNRS abstract release 

“Discovery and Characterization of the Exoplanets WASP-148b and c. A Transiting System with Two Interacting Giant Planets,” G. Hébrard et al., 2020, to appear in Astronomy & Astrophysics (Preprint on arxiv.org)