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Some exoplanets around red giant stars may be no more than an optical illusion. Variations in starlight that appear to be caused by orbiting worlds could come from ripples in the stars’ surfaces instead.
One method for finding stars relies on measuring changes in the star’s velocity as an orbiting planet makes it wobble back and forth. Because those movements are too small to detect directly, we find them by looking for how they affect the colour of the star’s light.
William Cochran at the University of Texas at Austin and his colleagues examined years of data from four different observatories to characterise the “wobble” of a star called Gamma Draconis. It is a red giant star, similar to the behemoth the sun will eventually evolve into, 154 light years away.
From 2003 to 2011, the star’s wobbly signal seemed to