Earth’s early history is marked by massive collisions with other objects, including planetesimals. One of the defining events in our planet’s history, the formation of the Moon, likely resulted from one of these catastrophic collisions when a Mars-sized protoplanet crashed into Earth. That’s the Giant Impact Hypothesis, and it explains how the collision produced a torus of debris rotating around the Earth that eventually coalesced into our only natural satellite.
New research strengthens the idea that Theia left some of its remains inside Earth.
Piecing together the history of the Solar System from the traces left behind isn’t easy. Bit by bit, however, we’re working it out. This month, new research examining the composition of lunar meteorites offers compelling evidence that the Moon and the Earth were formed from the same material, perhaps in the aftermath of a cataclysmic collision some 4.5 billion years ago.
Our conventional models of planet formation may have to be updated, according to a pair of new papers.
Accretion is the keyword in current planet formation theory. The idea is that the planets formed out of the solar nebula, the material left over after the Sun formed. They did this through accretion, where small particles accumulate into more massive objects. These massive boulder-sized objects, called planetesimals, continued to merge together into larger entities, sometimes through collisions. Eventually, through repeated mergers and collisions, the inner Solar System was populated by four rocky planets.
But the new research suggests that the collisions played out much differently than thought and that objects collided with each other several times, in a series of hit and runs, before merging. This research fills some stubborn holes in our current understanding.
According to the Giant Impact Hypothesis, the Moon formed when a Mars-sized object (named Theia) collided with Earth billion years ago, at a time when the Earth was still a ball of magma. This event not only led to the Earth-Moon system we recognize today, it is also beleived to have led to the differentiation of the Earth’s core region into an molten Outer Core and a solid Inner Core.
However, there has been an ongoing debate as to the timing of this impact and how long the subsequent formation of the Moon took place. According to a new study by a team of German researchers, the Moon formed from a magma ocean that took up to 200 million years to solidify. This means that the Moon finished forming about 4.425 billion years ago, or 100 million years later than previously thought.
A new study shows that the Moon is more metal-rich than previously thought. That has some far-reaching implications for our understanding of the Moon’s formation. If their results are solid, it means that we may need to re-think the giant impact hypothesis for the formation of the Moon.
The Moon is easily the most well-studied object in the Solar System, (other than Earth, of course.) But it still holds some puzzles for scientists. Why, for instance, is one side of the Moon so different from the other?
According to the most widely-accepted theory, the Moon formed roughly 4.5 billion years ago when a Mars-sized object named Theia collided with Earth (aka. the Giant Impact Hypothesis). This impact threw up considerable amounts of debris which gradually coalesced to form Earth’s only natural satellite. One of the most compelling proofs for this theory is the fact that the Earth and the Moon are remarkably similar in terms of composition.
However, previous studies involving computer simulations have shown that if the Moon were created by a giant impact, it should have retained more material from the impactor itself. But according to a new study conducted by a team from the University of New Mexico, it is possible that the Earth and the Moon are not as similar as previously thought.
The most comprehensive and widely-held theory of how the Moon formed is called the ‘giant impact hypothesis.’ That hypothesis shows that about 150 million years after the Solar System formed, a roughly Mars-sized planet named Theia collided with Earth. Though the timeline is hotly-debated in the scientific community, we know that this collision melted Theia and some of Earth, and that molten rock orbited around Earth until it coalesced into the Moon.
But now a new study, though not contradicting the giant impact hypothesis, is suggesting a different timeline, and an older Moon.
Scientists at the University of Munster have discovered that Earth got its water from a collision with Theia. Theia was the ancient body that collided with Earth and formed the Moon. Their discovery shows that Earth’s water is much more ancient than previously thought.
Since the late 19th century, scientists have struggled to explain the origin of the Moon. While scientists have long-theorized that it and the Earth have a common origin, the questions of how and when has proven to be elusive. For instance, the general consensus today is that an impact with a Mars-sized object (Theia) led to the formation of the Earth-Moon System shortly after the formation of the planets (aka. the Giant Impact Hypothesis).
However, simulations of this impact have shown that the Moon would have formed out of material primarily from the impacting object. This is not borne out by the evidence, though, which shows that the Moon is composed of the same material Earth is. Luckily, a new study by a team of scientists from Japan and the US has offered an explanation for the discrepancy: the collision took place when Earth was still composed of hot magma.