Astronomers have discovered an unusually massive, dense exoplanet that challenges conventional ideas about how rocky planets form.
Called GJ 523b, the exoplanet is about 2.5 times wider than Earth but packs roughly 23 times our planet's mass into that relatively compact size. Worlds this large and dense are sometimes referred to as "mega-Earths," an informal term for unusually massive, predominantly rocky planets. GJ 523b's high density suggests it contains relatively little atmosphere despite being large enough that astronomers would normally expect it to have accumulated a substantial gaseous envelope, according to a statement from the University of Wisconsin–Madison.
"This isn't what we expected at all," Max Kroft, lead author of the study, said in the statement. "Dense planets like this aren't uncommon, but they're usually small rocky planets similar to Earth or Mercury. This planet is two and a half times bigger than the Earth."
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