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View Full Version : Astronomers Now Looking For Exomoons Around Exoplanets



Fraser
2008-Dec-14, 09:20 AM
It looks like astronomers have already grown tired of taking direct observations of exoplanets, been there, done that. So they are now pushing for the next great discovery: the detection of exomoons orbiting exoplanets. In a new study, a British astronomer wants to use a technique more commonly associated with the indirect observation of exoplanets. [...]

More... (http://www.universetoday.com/2008/12/14/astronomers-now-looking-for-exomoons-around-exoplanets/)

Ilya
2008-Dec-15, 01:10 AM
On the page linked above someone wrote a very reasonable question:

Wouldn't the gravitational effects of the planet AND the moon on the star combine as if it were a single gravitation source, centered on the planet-moon system's center of mass?
Really, wouldn't that be the case? And if not, why not?

tdvance
2008-Dec-15, 02:04 AM
Not if there's more than one large moon.

timb
2008-Dec-15, 02:14 AM
On the page linked above someone wrote a very reasonable question:

Really, wouldn't that be the case? And if not, why not?

That may be so but I don't see the relevance to the variations in the time of transit. In the no moon case the transit time is predictable from the Keplerian orbit of the planet and the planet's diameter. If you've worked these out and the transit time is slightly different than predicted then difference may be attributable to a moon. Think about a transit of Earth seen by a distant observer. You can imagine that the barycenter of the Earth-Moon system orbits the Sun while the Earth (and moon) orbit the barycenter. This means that sometimes the component of the Earth's velocity tangential to its orbit is faster, sometimes slower than you would predict if all you had were the elements of the barycenter's orbit around the Sun. This may cause both the time between transits and the duration of transits to vary.