The extreme surface conditions of our post-collision Moon
When a ten-mile-long asteroid hit the Earth 65 million years ago, it resulted in death and destruction on a scale that’s hard to comprehend. When an object the size of Mars hit the Earth 4.5 billion years ago, there wasn’t anything alive to kill, which is good because the amount of destruction was completely off the charts. Both the Earth and the other object, a would-be planet named Theia, were basically reborn in violent swirl of molten rock and metal. In the end, the Earth was left with a new moon born from some of the debris, but it would be at least a thousand years before either body would even resemble the locations we know today.
As you might imagine, smashing two planet-sized objects together creates a lot of friction and heat. In the immediate aftermath of the collision with Theia, it’s estimated that the surface of the Earth was close to 3,632° Fahrenheit, hot enough to melt gold, iron and rock, but not hot enough to start spontaneously welding those metals together. However, the Earth would have still glowed with dim red light like a red dwarf star, and heated one half of the Moon up to 3,092°.
Flowing metal and very fast wind
Being cooked at close range would have made some dramatic changes to the composition of our Moon. Instead of the cold, dusty satellite we now know, the Moon would have been covered in a sea of molten metals like sodium. The metal would have been heated enough to have some material evaporate into a considerable, if temporary, atmosphere. That metal-based air would have been as thick as 1/10th the thickness of Earth’s, and it would have been blowing violently around the Moon at over half-a-mile a second, whipping up waves of liquid sodium in the process.
The reason for the wind is that for as hot as the Earth-facing side of this molten Moon would have been, the opposite side would have been extremely cold. Despite the layer of evaporated sodium, the dark side of the Moon would have been -238° Fahrenheit. As the scorching hot atmosphere blew into the darkness, it would probably have started to freeze, leaving a layer of sodium “snow” as it cooled.
Search for the sodium
The above scenario is based on simulations, but the frozen sodium atmosphere may provide a way to test if this is an accurate model or not. While much of this super-heated atmosphere would have been blown into space, as the Moon isn’t good at holding on to gases, the sodium that quickly froze should be preserved in the rocks and dust. Finding a ring of extra sodium near the transition between the light and dark sides of the Moon would therefore support this model of the satellite’s wild, frenzied origins.
Source: The moon might have had a heavy metal atmosphere with supersonic winds by Lisa Grossman, Science News