Planets much smaller than this don't cause wobbles big enough for us to measure in stellar spectra -at least, not yet. Gigantic orbiting planet finders now on the drawing boards might be able to detect Earth-sized worlds within 20 years or so. One other thing. Some of these worlds occupy orbits much smaller than the orbit of Mercury, the nearest planet to the Sun. The combination of huge planets on tiny orbits is challenging our ideas of how solar systems are made.
Astronomers wonder if the layout of our solar system is fairly common, or if it's a special case.
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