Moon’s precursor planet Theia vanished billions of years ago, leaving no direct chemical traces.
Astronomers in France, Germany and the United States analysed ancient lunar and terrestrial rocks to track its birthplace.
Researchers now argue that a long-lost planet involved in forming the Moon likely developed far nearer to the Sun.
They assert that Theia, believed to have shaped the Moon through a massive collision, emerged from the inner Solar System.
Scientists have long supported the giant impact theory, which states that Theia struck young Earth around 4.5 billion years ago.
Debris from the crash created the Moon, with fragments from Theia landing in both bodies.
Experts first discussed the idea more than 50 years ago after analysing Apollo samples.
Theia’s disappearance left no direct evidence, making its makeup and origin difficult to pinpoint.
Astronomers now use ancient rock samples to reconstruct Theia’s path through early space.
Jake Foster from the Royal Observatory Greenwich said the research identifies Theia’s birthplace with striking accuracy.
He noted that Theia no longer exists because the impact destroyed it completely.
He added that scientists can still determine its origin by examining surviving chemical signatures.
Tracking Chemical Clues
Researchers used Earth rocks and Apollo lunar samples to study their isotopes.
These isotopes act as chemical fingerprints that reveal planetary origins.
Scientists already knew that Earth and Moon samples share almost identical metal isotope ratios.
That similarity has limited knowledge of Theia because researchers struggled to separate early Earth material from impact debris.
The new study applies a form of planetary reverse engineering to solve this problem.
Scientists examined isotopes of iron, chromium, zirconium and molybdenum in both sets of samples.
They modelled hundreds of early Solar System scenarios to identify which combinations could produce today’s isotope patterns.
Materials close to the Sun formed under distinct temperatures and conditions, shaping their isotope signatures.
These variations allow scientists to map where objects originated in the early Solar System.
By comparing these patterns, researchers concluded that Theia formed in the inner Solar System.
They believe it orbited even closer to the Sun than early Earth.
Earlier theories proposed that Theia may have formed farther from the Sun.
New Paths for Planetary Science
Scientists hope this analysis will guide future investigations into how planets grow and collide.
Researchers expect these findings to help explain how early solar systems evolve over time.
The study offers a new way to understand the forces that shaped Earth, the Moon and other planetary bodies.
Its detailed modelling gives scientists a clearer picture of the chaotic conditions that shaped the young Solar System.
