Complex sentence: This planet, at a minimum mass of 1.9 Earths, was the least massive confirmed exoplanet identified around a main-sequence star until the confirmation of HD 10180 b. It takes just under 3.15 days to orbit Gliese 581.
Split into simpler sentences: This planet, at a minimum mass of 1.9 Earths, was up to then the least massive confirmed exoplanet identified around a main-sequence star. Until the confirmation of HD 10180 b. It takes just under 3.15 days to orbit Gliese 581.