By Nadia Drake
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.
That discrepancy is of great interest to astronomers, because the number of planets in the weight class just above Earth hints at how many bodies of terrestrial proportions are likely to be discovered.