Scientists have proposed a shocking new theory for the origin of the moon, and their calculations suggest Earth once had a secret world hiding right next door.
Astronomers believe that the moon was formed 4.5 billion years ago when a Mars–sized object called Theia smashed into Earth.
Theia was completely destroyed in the collision and only remains as traces of minerals in Earth’s crust and the moon.
Now, scientists from the Max Planck Institute for Solar System Research say they have finally uncovered Theia’s mysterious origins.
By looking carefully at the ratios of minerals in the Earth and the moon, researchers have worked out where Theia likely formed.
Lead author Dr Timo Hopp told Daily Mail: ‘Theia was likely one of tens to hundreds of planetary embryos that collided to form the planets.’
Dr Hopp suggests that Theia was once on a stable orbit within the inner solar system, sitting just closer to the sun than Earth is today.
That means, for the first 100 million years of the solar system’s existence, Earth had a hidden neighbour that has now totally vanished.
Scientists have proposed a new theory of the moon’s origin that suggests that Earth had a secret neighbour for the first 100 million years of the solar system’s existence (artist’s impression)
When Theia collided with the Earth, all the material that survived the impact was swallowed up into the Earth or the moon.
If any debris did escape, it was shot out of a stable orbit and has long since disappeared beyond the reach of scientific study.
So, even though scientists are confident Theia did exist, it’s proven extremely difficult to work out what it would have been like.
However, all the material in the solar system today still holds clues about its origin.
Isotopes are variants of elements that have different numbers of neutrons in their atomic nucleus.
In archaeology, researchers look at the levels of these isotopes, such as Carbon 14, in the process of carbon dating to work out the age of biological material.
In astronomy, scientists are able to make use of a similar process.
When the solar system formed, the isotopes of the various elements weren’t distributed evenly.
Researchers think the moon was formed when a Mars–sized planet named Theia hit ancient Earth. During the collision, Theia and proto–Earth mixed together to create our planet and the moon
That means rocks in the outer reaches of the solar system have a different ratio of isotopes to those found closer to the sun.
In their paper, published in the journal Science, Dr Hopp and his co–authors used this fact to work out where Theia might have formed.
They took extremely precise measurements of the iron isotopes in rocks from the Earth, moon rocks brought back by the Apollo missions, and several asteroids.
This revealed that the moon and Earth had identical ratios of iron isotopes, matching what had previously been found for other elements.
The samples’ similarity means that Theia and proto–Earth must have mixed together so thoroughly that they became indistinguishable.
Unfortunately, this makes it impossible to work out how much of Theia ended up in the moon and how much became a part of Earth.
‘The similar isotopic composition makes it also impossible to directly measure the initial composition of Theia,’ says Dr Hopp.
However, the researchers were able to work this out indirectly by comparing the moon and Earth to meteorites from different parts of the solar system.
Scientists now say that Theia likely formed in the inner solar system, and existed on a stable orbit just closer to the sun than Earth (file photo)
By looking at the composition of the Earth and moon today, the researchers looked at the different scenarios that could have led to this situation.
If Theia were similar to meteors that formed in the cooler outer edges of the solar system, proto–Earth would have needed to have a totally improbable mix of isotopes
Instead, both Theia and the proto–Earth were most likely made out of rocky ‘non–carbonaceous’ meteors from the innermost regions of the solar system.
Theia would have orbited the sun for around a hundred million years before the gravitational pull of Jupiter knocked it from its orbit and sent it careening into Earth.
Dr Hopp says: ‘It was on a relatively stable orbit around the Sun. We infer that this must have been closer to the Sun than Earth, however, that is all we can say.
