The Moon is over 4.4 billion years old and younger than once thought, says study that traced satellite's origins

A new study traces its origins to 4.425 billion years ago, making it 85 million years younger than the previous estimate. The event took place right after our planet came into being


                            The Moon is over 4.4 billion years old and younger than once thought, says study that traced satellite's origins
(Ron Miller)

The Moon and the Earth have had each other for company for millions of years. But when exactly did the lunar body form? A new study traces its origins to 4.425 billion years ago, making it 85 million years younger than the previous estimate. The event took place right after our planet came into being. Earlier estimates put the Moon's age at 4.51 billion years. When scientists reconstructed the events that led up to its formation, they realized it could be slightly younger. "Our calculations show that this most likely happened at the very end of Earth's formation," says Sabrina Schwinger, co-author of the study, describing the chronological sequence of events.

About 4.5 million years ago, the solar system was bustling with activity. The dust and gas were giving rise to new planets. At some time when the Earth was still developing, it was involved in a collision with a Mars-sized protoplanet. The clash threw out some debris into space, which then fused to form the Moon. It probably took 1000 years for the formation to happen, explains Doris Breuer, Head of the Planetary Physics Department at the DLR Institute of Planetary Research and a co-author of the study.

"The results of our latest modeling suggest that the young Earth was hit by a protoplanet some 140 million years after the birth of the Solar System 4.567 billion years ago," says Maxime Maurice, summarizing the team's investigations. "According to our calculations, this happened 4.425 billion years ago – with an uncertainty of 25 million years – and the Moon was born."

The Moon's magma ocean. (NASA/Goddard Space Flight Center)

Scientists have not reached a consensus on the Moon's age. Lunar rock samples collected by astronauts of the six Apollo missions and the three Soviet Luna robotic missions have not helped much. So Kleine and his team had to come up with an indirect means of doing so. "

So they turned to computer modeling to retrace the past. Their analysis showed that the energy released from the fusion of debris created a magma of ocean, thereby melting the lunar body. The team then calculated the age by estimating the time the Moon took to cool off and solidify. Their study showed that the Moon remained in the molten state for 200 million years. It later cooled and solidified, giving rise to the outer surface that we see today. “The time scale is much longer than calculated in previous studies,” adds DLR colleague Nicola Tosi, second author of the study. “Older models gave a solidification period of only 35 million years.”

They also found that the composition of minerals changed at different steps of the solidification process. Different types of rock on the Moon were dated to specific stages in the evolution of the magma ocean. “By comparing the measured composition of the Moon’s rocks with the predicted composition of the magma ocean from our model, we were able to trace the evolution of the ocean back to its starting point, the time at which the Moon was formed,” explains Schwinger.

The study is published in the Journal Science Advances.

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