Differential rotation in stars and planetary orbits

I sometimes have research ideas that I think are cool, but that don’t make sense for me to pursue. I generally just make a note of them and move on. This is the seventeenth post in a series describing some of the ideas I’ve accumulated.

Differential rotation in stars and planetary orbits

What’s the idea?

Stars exhibit differential rotation. At the same time, tides tend to bring stellar rotation rates and planetary orbits closer together in period. So: does differential rotation in a host star change the orbital evolution of its planets?

Why is this important?

Planets are intrinsically interesting, and their properties are strongly determined by their orbits. Think how hot they are, what volatiles are in their atmospheres, etc.

My guess is that this is a minor effect in most systems. Stars are so much more massive than their planets that it’s hard to lock the star to the planet’s orbit, and in cases where the mass ratio is less extreme (e.g. M-dwarfs) the differential rotation tends to be quite small.

As is often the case in astronomy though, the universe is big enough for rare things to happen, so this could be interesting to look at.

How can I get started?

I’d start by figuring out which part of the star an orbiting planet tries to synchronize to. Some collaborators and I worked out a very simple theory for this in the case of binary stars in this paper but there are definitely ways to improve on this.

Theory in hand, I’d suggest looking for systems where the star’s rotation is nearly-synchronized with a planet’s orbit. The only example I know of right now it Tau Bootis, but there could well be others. It would be interesting to calculate the impact of moderate differential rotation profiles on the orbital evolution of such systems to see if it matters to any significant degree.