TEHRAN
(FNA)- New clues suggest the moon resulted from a head-on collision
between Earth and another forming planet, according to scientists.
Researchers
from a team lead by the University of California, Los Angeles (UCLA)
analyzed lunar and volcanic rocks before concluding the moon was formed
during a violent head-on collision between an early Earth and another
forming planet called Theia.
Scientists knew Earth had been involved in a
high-speed crash almost 4.5 billion years ago, but they thought the
crash with Theia had been a 45-degree angle sideswipe. After studying
seven lunar rocks brought back by the Apollo 12, 15 and 17 missions, as
well as six volcanic rocks from the Earth’s mantle, they found that
Theia and Earth had had a head-on collision, rather than just a
fender-bender.
The scientists said the clue lay in the chemical
signature of the rocks’ oxygen atoms. Oxygen makes up 90 percent of
rocks’ volume and 50 percent of their weight. More than 99.9 percent of
Earth’s oxygen is 0-16, meaning each atom contains eight protons and
eight neutrons. There are small quantities of heavier oxygen isotopes,
such as 0-17, which has an extra neutron, and 0-18, which has two extra
neutrons. All of the planetary bodies in our solar system have a
distinct “fingerprint” of 0-17 to 0-16 isotopes.
A team of German scientists ventured in a 2014
issue of Science that the moon had its own unique ratio of oxygen
isotopes, which is different from Earth’s, but UCLA scientists found
“that is not the case.”
“We don’t see any difference between the Earth’s
and the moon’s oxygen isotopes; they’re indistinguishable,” said Edward
Young, lead author of the new study and a UCLA professor of geochemistry
and cosmochemistry, in a statement.
Using UCLA’s new mass spectrometer, the team
performed ultra-high precision oxygen isotope analyses of the lunar
samples and were able to deduce that if Theia had sideswiped Earth, the
moon would have been made mainly of Theia, and would have different
isotypes than Earth. The fact that the Earth and the moon share the same
chemical signatures contradicted the theory.
“Theia was thoroughly mixed into both the Earth
and the moon, and evenly dispersed between them,” Young said. “This
explains why we don’t see a different signature of Theia in the moon
versus the Earth.”
The crash with Theia happened approximately 100
million years after the Earth formed, almost 4.5 billion years ago. The
merging of the two planets also suggests why the moon is less dense than
the Earth.
Young and other scientists think Theia was
approximately the same size as the Earth, while others believe it was
more similar in size to Mars.
This is not the first time the theory of a head-on
collision has been proposed. In 2012, the theory was proposed by Matija
Cuk, now a researcher with SETI Institute; Sarah Stewart, now a
professor at UC Davis; and Robin Canup of the Southwest Research
Institute.
The paper, called Oxygen isotopic evidence for
vigorous mixing during the Moon-forming giant impact, by Edward Young,
Issaku Kohl, and Paul Warren, was published in Friday’s edition of Science.
Violent, Head-To-Head Crash between Earth, Another Planet Created Moon
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