He tata ki te 3.5275 g / cm3, ko te tino teitei o tetahi marama i roto i te Solar System; nui ake i era atu a Galileian satellites (Ganymede me Callisto i roto i te nuinga, ko o ratou densities e pā ana ki 1.9 g / cm3) me te iti ake (~ 5.5%) i te Moon 3.344 g / cm3. Tauira i runga i te Voyager me Galileo inenga o Io's papatipu, radius, me quadrupoleitational taumahatanga (uara tau e pā ana ki te pehea te papatipu te tohatoha i roto i te) kua whakaaturia e tona hanganga roto i waenganui i te silicate-rahi, me te kākahu rino-me te rino-i roto i te kopu o Io's. Heoi, i runga i te i te 50 km i raro i te 2011 (Kei te hiahiatia e tenei i roto i te 10 km i raro i te 50 km) he nui ake i te 75% o te papatipu o te marama i roto i te marama o Io's, e kore e taea te kitea i roto i te marama o te marama o te marama i roto i te marama
20% o ngā hua