The currently accepted hypothesis of how our Moon formed is that of a collision between Earth and a small proto-planet. This is supposed to have taken place about 4.5 billion years ago, when both bodies were still malleable hot.
Boy, that would have been a sight! From a distance of course.
It goes something like this: Earth, still nearly hot as lava, gets smacked in the kisser by a small wandering body in the same state of formation. Maybe like two mudballs. The smaller body is mostly absorbed into Earth’s core as it gouges out a mass of Earths crust. The resulting debris goes into low orbit, forming a lumpy ring around Earth. As the debris coalesces its orbit gets higher. Eventually a spherical body forms in orbit around Earth, a body we will one day call the Moon.
That hypothesis still stands, but recent evidence might give us hope of identifying what the rude interloper (we call it Theia) was made of. It also suggests a new hypothesis, that of a larger object, one nearly the same size as Earth and a little denser, did the deed. If that was the case, there might still exist a significant collection of Theia’s remains. Don’t get too excited, even if exists it will be deep within Earth’s mantle.
Computer models using an impactor the size of Earth and between 1.5 and 3.5% denser show an eventual collection of Theia rock near Earth’s core. How does one verify this?
Not a problem, seems geophysicists have known about two continent-sized collections of rock near Earth’s core for some time. They are located under the Pacific Ocean and Africa. Studies of earthquake seismic waves show seismic waves move more slowly through this rock compared with surrounding mantle. This indicates a denser material with different chemical makeup. Of course, these massive collections of rock have an interesting name – Large low-shear-velocity provinces (LLSVPs). While they have been known to geophysicists for years, their origin has been an enigma. The prevailing hypothesis is they were caused by discharges of heat (4,000 K) from the core, resulting in plumes of molten material that coalesced into high density slabs. A new, bigger Theia impactor hypothesis also fits LLSVP formation assuming some of Theia’s iron core got mixed with mantle on impact, increasing the mantle material’s density.
The challenge is this rock formation gets only as close as 1200 miles below Earth’s surface. I don’t think anyone has that much drilling pipe! However, some volcanic lava flows appear to reach one LLSVP so sampling from them might give clues to the LLSVP’s nature. Then let’s compare those findings with lunar mantle samples.
SUMMER’S HERE! (Like you didn’t know.) Summer Solstice occurs on June 20, 10:32 pm CDT
What’s in the Sky?
June 21-23; 90 minutes after sunset; west-northwest: Watch Mars photobomb M44, the Beehive Cluster in cancer. Use binoculars, spotting scope or telescope.