# I have seen so many articles but how can finding exoplanet density determine composition

I have seen some articles and lectures that state but i cant seem to put my finger on on how does density affect composition and how are you able to determine composition from exoplanet density.

• Density does not determine composition uniquely, particularly not with the massive error bars that current mass determinations still have. But it can constrain them, setting gaseous from non-gaseous planets broadly apart. – AtmosphericPrisonEscape Sep 17 '20 at 2:27

• You need BOTH the mass and density to make these judgements. Gas giants can have densities in excess of 10 g/cm$^3$. – ProfRob Sep 16 '20 at 21:21