Earth's Gravity May Have Kept the Early Moon's Volcanic Heart Beating

We typically think of the Moon as a static, floating object that has remained the same for basically its entire lifetime, with an occasional asteroid impact serving as an exception. That understanding is grounded in physics - the Moon should have cooled rapidly after forming when a huge protoplanet hit the early Earth around 4.5 billion years ago. But, some lunar material returned from the Change-5 mission was notably formed only around two billion years ago, yet appeared to be volcanic in origi...