Researchers Propose New Theory on How the Moon was Formed

January 9, 2017
Kevin Hattori

The Moon, and the question of how it was formed, has long been a source of fascination and wonder. Now, a team of Israeli researchers suggests that the Moon we see every night is not Earth’s first moon, but rather the last in a series of moons that orbited the Earth in the past. The findings by the team of researchers from the Technion-Israel Institute of Technology and the Weizmann Institute of Science are published today in Nature Geoscience.

The newly proposed theory by researchers Prof. Hagai Perets, of the Technion, and Weizmann Institute Profs. Raluca Rufu (lead author) and Oded Aharonson, runs counter to the commonly held “giant impact” paradigm that the moon is a single object that was formed following a single giant collision between a small Mars-like planet and the ancient Earth.

“Our model suggests that the ancient Earth once hosted a series of moons, each one formed from a different collision with the proto-Earth,” said co-author Prof. Perets. “It’s likely that such moonlets were later ejected, or collided with the Earth or with each other to form bigger moons.” To check the conditions for the formation of such mini-moons or moonlets the researchers ran 800 simulations of impacts with the Earth.

The new model is consistent with science’s current understanding of the formation of the Earth. In its last stages of the growth, the Earth experienced many giant impacts with other bodies. Each of these impacts contributed more material to the proto-Earth, until it reached its current size.

“We believe the Earth had many previous moons,” said Prof. Perets, who added that, “a previously formed moon could therefore already exist when another moon-forming giant impact occurs.”

The tidal forces from the Earth could cause moons to slowly migrate outwards (the current Moon is slowly doing that at a pace of about 1 cm a year). A pre-existing moon would slowly move out by the time another moon forms. However, their mutual gravitational attraction would eventually cause the moons to affect each other, and change their orbits.

“It’s likely that small moons formed through the process could cross orbits, collide and merge”, said Prof. Rufu. ”A long series of such moon-moon collisions could gradually build-up a bigger moon – the Moon we see today.”

The Technion-Israel Institute of Technology is a major source of the innovation and brainpower that drives the Israeli economy, and a key to Israel’s renown as the world’s “Start-Up Nation.” Its three Nobel Prize winners exemplify academic excellence. Technion people, ideas and inventions make immeasurable contributions to the world including life-saving medicine, sustainable energy, computer science, water conservation and nanotechnology. The Joan and Irwin Jacobs Technion-Cornell Institute is a vital component of Cornell Tech, and a model for graduate applied science education that is expected to transform New York City’s economy.

American Technion Society (ATS) donors provide critical support for the Technion—more than $2 billion since its inception in 1940. Based in New York City, the ATS and its network of supporters across the U.S. provide funds for scholarships, fellowships, faculty recruitment and chairs, research, buildings, laboratories, classrooms and dormitories, and more.