Sentence:  In the past two years, NASA's Kepler Space Telescope has located nearly 3,000 exoplanet candidates ranging from sub-Earth-sized minions to gas giants that dwarf our own Jupiter. Their <WSD>densities</WSD> range from that of styrofoam to iron. 
Meaning of the word marked with <WSD> tags:  (physics: amount of matter contained by a given volume) A measure of the mass of matter contained by a unit volume.