<Li> 3 . Rock </Li> <P> Pluto's density is 7003186000000000000 ♠ 1.860 ± 0.013 g / cm . Because the decay of radioactive elements would eventually heat the ices enough for the rock to separate from them, scientists expect that Pluto's internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice . The diameter of the core is hypothesized to be approximately 7006170000000000000 ♠ 1700 km, 70% of Pluto's diameter . It is possible that such heating continues today, creating a subsurface ocean of liquid water 100 to 180 km thick at the core--mantle boundary . In September 2016, scientists at Brown University simulated the impact believed to have formed Sputnik Planitia, and showed that it might have been the result of liquid water upwelling from below after the collision, implying the existence of a subsurface ocean at least 100 km deep . Pluto has no magnetic field . </P> <Table> Selected size estimates for Pluto <Tr> <Th> Year </Th> <Th> Radius </Th> <Th> Notes </Th> </Tr> <Tr> <Th> 1993 </Th> <Td> 1195 km </Td> <Td> Millis, et al. (if no haze) </Td> </Tr> <Tr> <Th> 1993 </Th> <Td> 1180 km </Td> <Td> Millis, et al. (surface & haze) </Td> </Tr> <Tr> <Th> </Th> <Td> 1164 km </Td> <Td> Young & Binzel </Td> </Tr> <Tr> <Th> 2006 </Th> <Td> 1153 km </Td> <Td> Buie, et al . </Td> </Tr> <Tr> <Th> 2007 </Th> <Td> 1161 km </Td> <Td> Young, Young, & Buie </Td> </Tr> <Tr> <Th> 2011 </Th> <Td> 1180 km </Td> <Td> Zalucha, et al . </Td> </Tr> <Tr> <Th> 2014 </Th> <Td> 1184 km </Td> <Td> Lellouch, et al . </Td> </Tr> <Tr> <Th> 2015 </Th> <Td> 1187 km </Td> <Td> New Horizons measurement (from optical data) </Td> </Tr> <Tr> <Th> 2017 </Th> <Td> 1188.3 km </Td> <Td> New Horizons measurement (from radio occultation data) </Td> </Tr> </Table> <Tr> <Th> Year </Th> <Th> Radius </Th> <Th> Notes </Th> </Tr>

In 1930 what name was not on the short-list of potential names for the planet pluto