Astronomers find 9 new planets and upset the theory of planetary formation
eurekalert.org
eurekalert.org
It's a serious question, I am curious. I don't know how they make these observations and thus whether or not the observations would be subject to strobe effect artifacts.
Other methods? In theory if the star's rotating fast enough and you see it side-on, then roughly half the star's light will be slightly blue-shifted (travelling towards you) and half will be red-shifted (away from you). As the planet crosses the star, it will block light coming from one half of the star, then light from the middle, then from the other half.
If there's a dip in the red-shifted part of the spectrum, in time transitioning to a dip in the blue, then you know the planet is moving against the star's rotation. If the dip is blue to red then you know it's following the star's rotation.
And my university lecturer (mentioned in the article) would be very disappointed that I can't remember the actual method of how it's done.
I think at that stage there was exactly one planet known in a retrograde orbit, but this new discovery shows that they're relatively common rather than being a one-off occurrence. Neato!
I don't think it challenges existing theories of planetary formation quite as much as is described in the article, since our existing theories of planetary formation are already pretty handwavey. I can easily imagine that a planet with a retrograde orbit could happen just due to collisions between large bodies during the planetary formation stage.
Oh, the other important thing to note is that the images are all "artists' conceptions". (Well, except for the one which shows two people in front of a telescope). Telescopes cannot possibly resolve a planet as a little dark disc in front of a big bright disc, so all these measurements just rely on the slight darkening of the star as the planet passes in front.
You can't actually visibly see the planet travel across the star, however. What you measure is the periodic dip in the number of photons collected by the CCD.
Also, these things are already in close orbit to the star. Strobing would imply that they are much closer than thought (to get the much faster orbit you are hypothesizing), and I doubt these "hot jupiters" would survive very long if they were 10 times closer then thought when they are already about as close as they can be.
I don't think it's always a 10x difference, but I haven't thought too hard about the math. I think the difference depends on the relation between the observation period and calculated orbital period based on the observations.
I can imagine a scenario where the difference would approach 0, the only difference being direction. For instance if your observation period is +/- 1% of an orbit, the major difference in orbit between the two predicted orbits would be direction, with only a minor difference in magnitude.