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In the search for planets beyond our solar system, the UK's Wide Area Search for Planets (WASP) has stumbled upon a bizarre-o world that is orbiting its star in reverse.

"I have to say this is one of the strangest planets we know about," Sara Seager, an astrophysicist from the Massachusetts Institute of Technology, told SPACE.com.

After stars spin up, they usually bring in nearby debris, which picks up the same directional orbit. "With everything [in the star system] swirling around the same way and the star spinning the same way, you have to do quite a lot to it to make it go in the opposite direction," Coel Hellier, of the UK's Keele University, told the BBC.

Indeed, the newly discovered exoplanet likely took a large close call with another even larger object to swing the planet (named WASP-17b) into a retrograde orbit. "If you have a near-collision, then you'll have a large gravitational slingshot from that interaction," Hellier said.

It's the first known planet to have such an unexpected orbit although some of the other planets' moons in our solar system fly a backward track around their planets.

http://www.scientificamerican.com/blog/ ... 2009-08-13

Can this be done in Celestia?

Reiko wrote:Can this be done in Celestia?

I'm not sure which "this" you mean.
Showing a planet orbiting in the opposite direction from the rotation of its sun is very easy and can be done in several different ways. One would be to specify the orbit's Inclination as 180 degrees.

Displaying the trajectories of two bodies interacting so that one of them winds up in such an orbit would be somewhat more difficult. One way to do that would be to use another program to do the gravitational calculations and write xyz trajectory files for the two planets. Another would be write ScriptedOrbit functions for each of the planets which calculate the planets' positions.

selden wrote:

Reiko wrote:Can this be done in Celestia?

I'm not sure which "this" you mean.
Showing a planet orbiting in the opposite direction from the rotation of its sun is very easy and can be done in several different ways. One would be to specify the orbit's Inclination as 180 degrees.

That's what I was wondering. If you put the inclination at 180 would the planet orbit in the opposite direction of the sun's rotation.

Reiko wrote:. If you put the inclination at 180 would the planet orbit in the opposite direction of the sun's rotation.

Yes.