scientists Pinpoint Origin of Moon-Forming Planet Theia to Inner Solar System
A groundbreaking new study offers the clearest evidence yet regarding the formation of Theia, the ancient planet that collided with Earth approximately 4.5 billion years ago, ultimately giving birth to the Moon. Published in the journal Science, the research reveals that Theia originated in the inner regions of the Solar system, remarkably close to our own planet.
For decades, the prevailing giant impact model has posited that the Moon was largely composed of debris from Theia. This theory implied significant chemical differences between Earth and the moon. However, years of measurements have demonstrated a surprising similarity in their chemical signatures, creating a long-standing puzzle for planetary scientists.
To resolve this conundrum, researchers focused on tracing the remnants of heavy elements left behind by Theia on Earth. Iron and molybdenum isotopes proved to be crucial clues in unraveling the mystery. A team led by thorsten Kleine at the Max Planck Institute for Solar System Research meticulously analyzed 15 terrestrial rock samples and six lunar samples returned by Apollo astronauts.
the team’s analysis centered on iron isotopes – variations of the element distinguished by differing numbers of neutrons. As one researcher explained, “The revelation of iron isotope anomalies is quite new. These analyses are tough,the changes are very small. That is why such a study has not been done on lunar samples until now.” Researchers also examined isotopes of molybdenum and zirconium, employing a “reverse engineering” approach to determine Theia’s size and composition.
The findings indicate that Theia was a rocky planet with a metallic core, possessing between 5 and 10 percent of Earth’s mass. Perhaps most significantly, the research establishes that Theia formed deeper within the Solar System than Earth, even further from the Sun than our planet’s orbit. This conclusion builds upon a 2020 study by Kleine, which demonstrated that objects forming closer to the Sun are enriched in heavy elements like molybdenum. The current measurements confirm that the excess molybdenum and zirconium found on Earth originated with Theia.
This new understanding elegantly explains the striking similarities between Earth and the Moon: both planets were forged from materials originating in the same region of the early Solar System.
“A big step in understanding our origins,” remarked planetary scientist Sara Russell of the Natural History museum in London, who was not involved in the study. she praised the “extraordinary sensitivity” of the measurements, adding, “These findings help us understand not only the origin of theia, but also how the Earth-Moon system evolved into a structure suitable for life.” Russell anticipates that future lunar explorations will build upon this analysis, stating, “It’s incredible that 50 years later we’re still learning new things from these samples collected by Apollo astronauts.”
The research team’s next step involves testing their Theia model through detailed giant collision simulations. kleine also indicated that they will continue to analyze lunar samples for other elemental isot
