Question: Do you think extraterrestrial life exists and is the moon hollow?

Mark Mirmelstein answered on 8 Mar 2018:

I would like to believe that some form of life does exist somewhere. We have discovered that there are so many planets orbiting other suns, that it makes it very likely that some form of life evolved somewhere else apart from on Earth. Moreover, there are several moons in our solar system that may have life – specifically Jupiter’s moon Europa, and Saturn’s moon Enceladus. Both of these moons may have an underground water ocean and perhaps also hot vents which may mean life could have evolved there. Several NASA missions are currently being planned to reach those moons and find out if there is indeed life there! This is super exciting if they have enough funding to carry out those missions.

Regarding the moon, from measuring its mass and its size, it is unlikely that it is hollow. If it were hollow it would have probably collapsed in on itself as well, or break apart due to its own gravity of the Earth’s gravity. Another hint that it is not hollow is that it is almost a perfect sphere, and according to our current understanding, such shape is formed over time, so the moon may have started as having an irregular shape which slowly turned into a spherical shape, which wouldn’t have been able to happen if it were hollow.