Thursday, 15 April 2010

Real Retrograde Orbits

Yes, this is weird.

Astronomers Amaury Triaud,Andrew Cameron and Didier Queloz put their heads and their observational data together and reported at a meeting of the Royal Astronomical Society earlier this week that, out of 27 randomly-select exoplanets, 6 of them were orbiting their primary star the wrong way.

An exoplanet is a planet orbiting a star other than the Sun. Up until now,all our widely-accepted theories of how solar systems form have made the prediction that planets will orbit their stars in the same direction that the star is rotating on its own axis.

For example, the coalescence theory imagines that the sun and all the planets formed out of a spinning disc of matter - the sun coalescing first, and then the planets gathering together from the accretion disc. You can picture it yourself with no difficulty, and you don't need higher maths to realise that the planets would obviously revolve around the sun in the same direction as the rest of the spinning disc.
Even tidal theories of solar system formation - in which a passing star pulls mass off another and draws it out into what become a bunch of attendant planets - would predict that the planets and the star would rotate/revolve in the same direction. The very simple notion of conservation of angular momentum would explain this conclusion.

So, now that we've found that almost a quarter of a random sample of exoplanets so far discovered are going the wrong way around their stars, what do we say?

Well, Amaury Triaud says this:

"This is a real bomb we are dropping into the field of exoplanets"

And, assuming that the phenomenon is not due to an observational error (and given the number of planets displaying it, that isn't very likely), I would say he's right.
It really looks like we will have to return to the drawing board for ideas and hypotheses as to how planetary systems form.

This could get even more interesting.