Image source, Getty Images/Mark Garlick
Next time you gaze at the full moon, please spare a thought for ‘Theia’.
About 4.5 billion years ago, scientists postulate that an imaginary planet collided with Earth, which they have named ‘Theia’.
The debris ejected from this tremendous impact is believed to have eventually coalesced to form the Moon.
According to this theory, if Theia had not sacrificed itself, our natural satellite, the Moon, would not exist—and you would not be reading this article.
A ‘Violent’ Collision
Scientists believe that the early Earth collided violently with a Mars-sized celestial body. They estimate that the fragments ejected by this cataclysmic event gradually gathered together to become the new Moon.
This hypothesis, called the ‘Giant Impact Hypothesis’, suggests that this collision played a crucial role in shaping Earth’s ability to foster life.
Over the ensuing billions of years, the gravitational tug-of-war between Earth and the Moon helped stabilize Earth’s axial tilt, providing us with a stable climate system.
“Without climate stability, there would be erratic climate and seasonal patterns here, which are unfavorable for the development of life,” explained Professor Thorsten Kleine of Germany’s Max Planck Institute for Solar System Research.
Professor Kleine was part of the international research team that studied this possible, immense and mysterious event in November of last year.
Their study, published in the journal ‘Science’, reported that the chemical analysis of Earth and Moon materials strengthened the belief that Earth and Theia were uneasy neighbors during the turbulent times of solar system formation.
Image source, NASA
One Moon, Many Theories
However, Theia was not always part of our collective thoughts. Before humans set foot on the Moon in 1969, there were three main theories about how the Moon came to be.
The ‘Fission’ theory suggested a rapidly spinning Earth ejected a large piece into space, which later became the Moon.
The ‘Capture’ theory held that the Moon formed elsewhere in the solar system and was subsequently captured by Earth’s gravity.
The ‘Co-formation’ theory proposed that Earth and the Moon formed together at the same time and stayed together.
Since none of these fully explained the evidence, NASA’s Apollo missions shifted the focus toward a new hypothesis.
Chemical Similarity
Although Neil Armstrong and other astronauts’ moonwalks were praised, the Apollo missions’ critical contribution was the ‘gifts’ they brought back.
“Apollo astronauts brought back lunar rock samples. When scientists tested them, they found chemical similarities with Earth’s rocks,” said Professor Ramon Prinz, an astronomer at University College London and author of the book ‘Wonders of the Moon’.
This finding suggests the Moon could have originated from Earth.
Image source, NASA/Getty Images
Prinz explains that the formation of these rocks involved extremely high temperatures, which indicate a violent collision had occurred.
The absence of easily vaporized elements suggests that materials on the Moon were once in a molten state.
According to NASA lunar geologist Dr. Sara Valencia, these samples provide subtle clues. Advances in technology, especially computer modeling in recent decades, have further reinforced the Giant Impact Hypothesis.
One prominent proponent suggests Earth’s axial tilt may have resulted from the collision with Theia.
“The Giant Impact Hypothesis remains the strongest explanation for the chemical and relational connection between Earth and the Moon,” Valencia stated.
Did Earth ‘Swallow’ Theia?
But what ultimately happened to Theia?
This remains an unresolved mystery. About 66 million years ago, a notorious celestial object struck Earth causing a massive crater in the Yucatan Peninsula of Mexico and the extinction of dinosaurs and other life. However, no crater associated with Theia has been found.
Kleine explains that Theia was about one-tenth the size of Earth. After the collision, most fragments were absorbed by Earth, while some flew off into space to form parts of the Moon.
“That is the expected outcome from such a collision, but structural evidence of Theia on the Moon has yet to be found,” the scientist added.
Image source, NASA/JPL-Caltech/Esa
“We believe that because Earth and Theia formed in the same region of the solar system, they shared many similarities,” she said.
We also know that Earth shares many similarities with its two closest planetary neighbors, Mars and Mercury. Mercury is sometimes called Earth’s ‘evil twin’.
However, just as Theia’s origin remains unclear, its end is also shrouded in uncertainty.
Some clues have emerged, though. A 2023 study claimed that two continent-sized regions deep within Earth may be remnants of Theia.
New Missions to the Moon
The precise formation of Earth and the Moon is still not fully known.
Therefore, NASA is preparing to launch its Artemis program to send humans back to the Moon, which excites scientists worldwide.
Image source, NASA
This new endeavor will enable much more advanced testing than Apollo missions and will explore previously unvisited areas such as the Moon’s South Pole. Apollo missions only brought back samples from limited locations.
“If we merely circumnavigated a sixth of Earth, would that mean we have fully explored the planet or understood its origins? Certainly not,” Valencia said.
However, based on current understanding, we can express our gratitude for Theia’s sacrifice.
