PDA

View Full Version : Biggest Exoplanet Yet Orbits the Wrong Way



Fraser
2009-Aug-12, 02:10 PM
Planet hunters from the UK have discovered the largest exoplanet yet, and its uniqueness doesn't end there. Dubbed WASP-17, this extra large world is twice the size of Jupiter but is super-lightweight, "as dense as expanded polystyrene" one astronomer said. Plus it is going the wrong way around its home sun, making [...]

More... (http://www.universetoday.com/2009/08/12/biggest-exoplanet-yet-orbits-the-wrong-way/)

schlaugh
2009-Aug-12, 05:19 PM
??? Retrograde in relation to....what? The spin direction of the star? (And can that even be determined?) Are there other planets in the system orbiting the other direction? The article doesn't say how the researchers came to that conclusion.

Ah, wait...let's see...the abstract says "Preliminary detection of the Rossiter-McLaughlin effect (http://en.wikipedia.org/wiki/Rossiter%E2%80%93McLaughlin_effect)suggests that WASP-17b is in a retrograde orbit (lambda ~ -150 deg), indicative of a violent history involving planet-planet or planet-star scattering."

Got it...light is blue-shifted in one quadrant (spinning towards the observer) then red-shifted (spinning away) which enables astronomers to record the star's spin direction. And WASP-17 is orbiting opposite to the star's spin.

Paul Beardsley
2009-Aug-12, 05:22 PM
Hmm, so the universe continues to throw out surprises.

Amber Robot
2009-Aug-12, 05:31 PM
Got it...light is blue-shifted in one quadrant (spinning towards the observer) then red-shifted (spinning away) which enables astronomers to record the star's spin direction. And WASP-17 is orbiting opposite to the star's spin.

You can see the effect in their Figures 3 and 6.

matthewota
2009-Aug-12, 05:37 PM
??? Retrograde in relation to....what? The spin direction of the star? (And can that even be determined?)

They claim it is spinning in the opposite direction of the star's rotation.
I would assume that they determined the star's rotation with spectroscopy.

GOURDHEAD
2009-Aug-12, 06:02 PM
Have they determined the spin of the planet on its axis? If both spin and orbital revolution are retrograde, would that imply the planet was captured from another system?

timb
2009-Aug-12, 11:38 PM
Have they determined the spin of the planet on its axis? If both spin and orbital revolution are retrograde, would that imply the planet was captured from another system?

No.

AndrewJ
2009-Aug-13, 05:11 AM
Have they determined the spin of the planet on its axis? If both spin and orbital revolution are retrograde, would that imply the planet was captured from another system?

If both spin and orbit are opposite to the star's the planet must have had quite a thump. Would be a real gem if it could be proved to have been a captured delinquent planet but then stars are such lonely, isolated souls that it seems improbable.

Gigabyte
2009-Aug-14, 05:55 PM
I for one, welcome our new WASP-17 Overlords.

matthewota
2009-Aug-14, 07:24 PM
The density information is interesting on its own. I wonder what the surface gravity would be? I wonder if you could stand on it?

timb
2009-Aug-14, 10:41 PM
Hmm, so the universe continues to throw out surprises.

Retrograde planets were predicted by theory. There's a small probability that the Kozai mechanism and planet scattering will put a planet into a retrograde orbit.

Ilya
2009-Aug-15, 12:41 AM
The density information is interesting on its own. I wonder what the surface gravity would be?
It is twice Jupiter's diameter and half Jupiter's mass, so surface gravity is 1/8 Jupiter, or 0.3 Earth.

I wonder if you could stand on it?
Considering it is almost certainly gas, no.

Paul Beardsley
2009-Aug-15, 08:36 AM
Retrograde planets were predicted by theory. There's a small probability that the Kozai mechanism and planet scattering will put a planet into a retrograde orbit.

Thanks for the information.

It's fair to say, though, that it surprised me!