Believe It or Not!
Before it crashed into the Moon in 2009, Chandrayaan-1, India’s first lunar probe, discovered mountainous outcroppings of crystal formed billions of years ago. Back then, the moon was a molten, hot mess of a world. Instead of solid rock, it was covered in a sea of lava that likely existed for a few hundred million years. How could it stay hot for so long? Lava here on earth hardens pretty quickly, after all.
Well, there are only 3 ways to cool off something that’s hot, conduction, convection and radiation. The moon doesn’t have an atmosphere, so convection wouldn’t work. At the time, everything would’ve been hot, so conduction wouldn’t work. That just leaves radiation, where the lava radiates its heat away in the form of infrared light. Radiation happens to be a really slow way to lose heat.
What caused all of this? Right now, the leading idea for how the moon came to be is the Giant Impact Hypothesis. Long story short: the Earth shared its orbit with a planet the size of Mars in the early days of the solar system. It hit the Earth and the ensuing collision blasts chunks of molten rock into orbit over the earth. Under its own gravity, the molten rock pulls together into a ball that rotates around the Earth and WHAM: Instant Moon.