

Astronomers find 9 new planets and upset the theory of planetary formation - instantramen
http://www.eurekalert.org/pub_releases/2010-04/uoc--afn041310.php

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apinstein
I'd imagine that they've thought of this, but how do they know that the
planets are truly moving backwards rather than just seeming that way due to a
planetary strobe effect (<http://en.wikipedia.org/wiki/Strobe_light>)?

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.

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teamonkey
Measurements are taken over a period of time. I assume that all the stars
looked at resolve to more than a few pixels wide on the CCD. In that case you
can visibly see the planet travel across the star in successive frames.

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.

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hugh3
Yes, I'm pretty sure all the measurements done in these sorts of studies are
done using the redshift-blueshift method you mentioned. A rotating star has a
"red" half and a "blue" half, and a planet transiting the star will cause
first a blueshift then a redshift, or a redshift then a blueshift. I went to a
talk on this subject a few months ago and was amazed by how sensitively they
can pick this kind of thing up.

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.

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haarpz
anyone getting any new news on HAARP - Earthquake ?

