Astronomers developed a new moon model to determine why Moon rock samples contain less volatile elements found on Earth.
Based on the highly supported Giant Impact Theory, the Moon was created out of a collision between a proto-Earth and Mars-sized planet scientists called Theia 4.5 billion years ago. The massive collision of Earth and Theia hurled debris into space, where they created a disk with approximately 19,900 kilometer radius.
The disk is made up of the young Earth's crust - vaporized and molten rocks which float around the Earth. The Moon was formed when the disk debris combined and solidified. Despite similarities in geology, scientists still do not know why volatile elements such as zinc, sodium and potassium found on Earth are fewer in rock samples retrieved from the Moon by Apollo astronauts.
Scientists believe that the Earth's gravity would have kept the element flung into space during the collision on track in the debris disk. But how come there are no traces of these elements on lunar rock samples?
A team of scientists led by Dr. Robin Canup from the Southwest Research Institute in Colorado created a new model of the moon formation using the combination of old and new theories.
Researchers found that the Moon's core was formed from debris found on the outer layers of the debris disk which was cool enough for volatile elements to turn from gas to liquid. The Moon's outer layer was formed from the inner layers of the debris disk, wherein, according to Canup's new model, was too hot for the volatile elements to turn from gas to solid.
This new model explains why lunar rocks have less of these volatile elements. While the inner debris disk cooled eventually to allow the elements to condense, the cooling stage took place after the Moon left the debris disk and when its formation was completed.
"The Moon's orbit expands enough to turn off its accretion, before the inner disc gets cool enough for the volatiles to condense. So by the time they do condense, they're scattered on to the Earth rather than swept up by the Moon," said Canup.
The astronomers published their study in the Nature Geoscience journal on Nov. 9.
Photo: Janet Ramsden | Flickr
