Satellites in prograde motion receive a momentum transfer from the rotating parent body, gradually rising in altitude.N2K Information For Star HD149026The orbital period of HD149026b is remarkably short, 2.88 days. In fact, for this "Hot Saturn", an entire "year" takes place over a single weekend! Orbiting at a distance of just 0.042 AU, the planet's would have a scorching temperature of 1,500 K... HD149026 is in the constellation Hercules in this part of the sky... Radial Velocities of the star HD149026 not only reveal the wobble due to the planet, but also deviate from a perfect sine wave when the planet passes in front of the rotating star. This is called the Rossiter-McLaughlin effect and has been observed for other transiting planets.
San Francisco State University
Satellites in retrograde motion transfer momentum to the parent body and lose altitude.
Generally it would seem to be impossible to determine the direction of orbit for an extrasolar planet.
Planets with these orbital characteristics and in prograde orbits were even closer to the parent stars in the past, meaning that they are of recent origin. Either they were captured, or were thrown off from the surface of the star.
Bodies in retrograde are generally believed to have been captured (this is the case with a number of moons of Jupiter). Planets with these orbital characteristics and in retrograde orbits are working their way closer to the parent stars.
Also an X-Planets posting:
