Complex sentence: One was potentially a large terrestrial planet, with less than 22 Earth masses and 1.8 Earth radii, the other is of similar mass at 15.2 Earth masses but with 3.6 Earth radii it is almost certainly a gas giant.
Split into simpler sentences: One was potentially a large terrestrial planet, of less than 22 Earth masses and 1.8 Earth radii. The other is of similar mass at 15.2 Earth masses, but with 3.6 Earth radii it is almost certainly a gas giant.