MessageToEagle.com - Science has yet to provide a satisfactory explanation of the origin of our closest neighbor - the Moon.
There are so many questions regarding the Moon, but perhaps two of them are most important:
Where did the moon come from, and how did it get there?
A new research based on lunar material collected by Apollo astronauts in the 1970s does not support the
widely held theory that a giant collision between Earth and a Mars-sized object gave birth to the moon 4.5
billion years ago.
In the giant-collision scenario, computer simulations suggest that the moon had two parents: Earth and a
hypothetical planetary body that scientists call “Theia.
” But a comparative analysis of titanium from the moon, Earth and meteorites, published by Junjun Zhang,
graduate student in geophysical sciences at the University of Chicago, and four co-authors indicates the moon’s
material came from Earth alone.
If two objects had given rise to the moon, “Just like in humans, the moon would have inherited some
of the material from the Earth and some of the material from the impactor, approximately half and half,” said
Nicolas Dauphas, associate professor in geophysical sciences at UChicago, and co-author of the study,
which appears in the March 25 edition of Nature Geoscience.
“What we found is that the child does not look any different compared to the Earth,” Dauphas said.
“It’s a child with only one parent, as far as we can tell.”
Formation of the Moon. Five hours after collision. Painting by William K. Hartmann based on computer simulation.
The researchers selected titanium for their study because the element is highly
refractory and titanium isotopes — forms of titanium that contain only slight
subatomic variations.
This means that titanium tends to remain in a solid or molten state rather than becoming a gas
when exposed to tremendous heat. The resistance of titanium isotopes to vaporization makes it less likely
that they would become incorporated by the Earth and the developing moon in equal amounts.
Titanium also contains different isotopic signatures forged in countless stellar explosions that occurred
before the sun’s birth. These explosions flung subtly different titanium isotopes into interstellar space.
Different objects in the newly forming solar system gobbled up those isotopes in different ways through
collisions, leaving clues that let scientists infer where the solar materials including the moon came from.
Credits: William K. Hartmann
“When we look at different bodies, different asteroids, there are different isotopic signatures. It’s like
their different DNAs,” Dauphas said.
However, oxygen isotopic compositions have been found to be identical between terrestrial and lunar samples,
which is inconsistent with numerical models estimating that more than 40% of the Moon-forming disk material was
derived from Theia.
Solving the conundrum of the moon’s origin probably will prove challenging because all of the alternative scenarios
for the moon’s formation have drawbacks.
An old idea, long abandoned, is that the moon arose via fission from a molten, rapidly rotating Earth following a
giant impact. This idea explains the similarity between Earth and moon, but how such a large, concentrated mass
could spin fast enough to split in two remains problematical.
Another scenario suggests that Earth collided with an icy body lacking entirely in titanium. There are no bodies
made purely of ice in the solar system, however.
“They would always have a significant fraction of solid material, so you would still expect the object to deliver
some titanium,” Dauphas said.
It’s also possible that Theia had the same composition as Earth. This is unlikely, however, because of the widely
accepted view that the Earth incorporated material over tens of millions of years in collisions with smaller bodies
that flew in from different regions of the developing solar system.
“We thought we knew what the moon was made of and how it formed, but even 40 years after Apollo, there is still
a lot of science to do with those samples that are in curatorial facilities at NASA,” Dauphas said.
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