The moon may be made from a magma ocean that once covered Earth

There are a number of theories about where the moon came from. Our best guess is that it was formed when the Earth was hit by a large object, throwing up tons of debris into orbit, which eventually formed the moon.

There's a problem with this theory. Models show that most of the material that makes up the moon should come from the object that ran into it, but most of the material—as the Apollo missions found—comes from Earth.

A paper in Nature Geoscience has a possible explanation. It suggests that the Earth at the time of impact was covered in hot magma rather than a hard outer crust. Magma can be dislodged much easier than a solid crust.

This theory relies a lot on timing. The Earth would have to be in a sweet spot of magma heat and consistency for the theory to be true. It also still doesn’t check all the boxes needed to get our lunar observations in line with our theories, but it’s an important step forward.                                                                     —Erin Winick