Now that known exoplanets have become almost as numerous as fireflies on a midsummer’s eve, two top planet-finding missions are starting to disagree over the abundance of low-mass planets that are heavier than Earth but smaller than Neptune.
The Swiss-led HARPS mission suggests that between 30 and 50 percent of sunlike stars in the solar neighborhood host super-Earths and sub-Neptunes. Meanwhile, NASA’s Kepler mission is finding that these planets circle roughly 15 percent of the stars in its far-flung field of view.
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