Hot Saturns

Having formulated an hypothesis that could account for so called "Inflatable Planets" (albeit not without some difficulty - though probably less than assuming the planet is made of balsawood) in a previous posting, I thought I'd ask one of the team members about it.

It was nice to get an informative reply from Francis O'Donovan of the TrES team:

there are indeed several theories abounding regarding the possibility of a
rings around TrES-4. I have not investigated this thoroughly, but my
understanding is that in order to have an opaque disk that could lead to a
larger apparent size for the planet, you need to have a ring made up of
very small dust particles (unlike Saturn's rings), and this dust would
likely be blown away. As you suggest, it might be a more recently formed
ring, but again it is unlikely that we would happen to observe it at that
time.

I look forward to seeing what the theorists have to say about TrES-4

And so do I - now that the Boltzmann Brains have been dealt with, Inflatable Planets are rising to the top of my watch list.

Inexplicable "Inflatable Planets" - Hot Saturns

Back in September 2006 New Scientist ran an article on "The riddle of the inflatable planets" in which Dimitar Sasselov said that the newly discovered planet HAT-P-1 was so light that it would float on water "like a beach ball."

Now New Scientist has reported today that another group The Trans-atlantic Exoplanet Survey (TrES) has found another particularly anomalous planet designated TrES-4, this one being "about the density of balsawood" [Balsawood! Does it have any uses other than model aircraft construction?]

Apparently, according to New Scientist, Travis Barman, a theoretician at Lowell Observatory, said, "This planet cannot exist.", i.e. there's no good explanation for how it could have become so large.

However, here's a hypothesis: the planet is not as large as it appears - the apparent size of the planet suggested by the observed dimming during transit could be due to a set of sufficiently dense rings. Saturn's rings are considerably wider than the planet, and they scatter quite a lot of light (though I'm not sure how much... I may be a geek but I'm not actually doing this research!)

I see two basic possibilities for the existence of rings around such "Hot Jupiters" (planets of Jupiter mass very close to their parent stars)

1. There could be a stable ring system. Intuitively this seems unlikely given, amongst other things, the considerable radiation pressure likely to be experienced so close to a star - dust would be driven off

2. There is a temporary ring system - it would wouldn't need to be stable, it could be recently formed. Perhaps if the planet had one or more moons, additional tidal heating from stellar proximity etc. might have expedited its disintegration and the formation of rings, in which case extended observation might record progressive dissipation of the rings and decrease in the dimming observed.

In either case, what would have been observed would be a "Hot Saturn" rather than a "Hot Jupiter", and the abnormally low density would be explained by the mis-estimation of the planet's size, i.e. mistaking the attenuation due to the ring system for attenuation due to the planet itself.

I wonder how this hypothesis could be observationally tested - actually I wonder whether it is viable at all... but that's what a bare hypothesis is: an idea for exploration...