Beware the Phantom Exoplanets
June 25, 2009
This is an added complication in the search for exoplanets I hadn't thought of before: confusing exoplanets with starspots.
Yes, starspots are pretty much the same thing as sunspots; patches of cool plasma exposed by magnetic flux pushing the hotter photosphere and chromosphere aside.
Similar mechanisms drive both sunspots and starspots, and huge spots or large swarms of smaller spots have been detected on the surface of distant stars. In some cases, these starspots can be very extreme, covering a huge area of the star (up to 30% of the star's total area in some cases).
Back in 2004 however, astronomers thought they'd made quite a different discovery. Studying an exoplanet orbiting a star called TrES-1 (in the constellation of Lyra, 500 light years away), international teams of astronomers confirmed the discovery, but noted that something else was orbiting the star.
The astronomers used the transit method to detect exoplanets, meaning they measured the dip in stellar brightness as the exoplanet passed in front of the star. Exoplanets are simply too small to be resolved with telescopes (actually, that's not entirely true), so we must depend on the exoplanet blocking some of the starlight from view to signify its presence.
Although it is attractive to think there might be another exoplanet out there producing this transit effect, it turns out that the exoplanet would have to be 745AU from TrES-1 with an orbital period of 21,000 years. At these kinds of extreme distances, the exoplanet would need to be gargantuan to produce any measurable change in stellar brightness!
In a publication released yesterday, Jason Dittmann and colleagues from the University of Arizona did the legwork and worked out that the phantom exoplanet was actually a giant starspot causing the dip in brightness.
Why do I feel a tinge of sadness in the air? It's kinda cool we can detect spots on distant stars... isn't it?
Source: arXiv blog
Comments
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I was tempted to say something about our missing sunspots but thought better ... oh, too late.
Posted by: mang | June 25, 2009 at 01:47 PM
Nice piece of work.
Some exoplanets are discovered by transit and reflected light as the planet begins to pass around behind the star casuing a brief brightening of the star. I know MOST looks for this as well.
Posted by: Mang | June 25, 2009 at 11:00 AM