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Mini-Moons Orbit Earth At All Times, Asteroid Study Suggests

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The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right along the yellow line and continues on its trajectory along the orange path and finally escapes capture along the red path to the upper right. The size of Earth and the Moon are not to scale but the size of the minimoon’s path is to scale in the Earth-Moon system.
The path of a simulated minimoon that is temporarily captured by Earth. The object approaches Earth from the right along the yellow line and continues on its trajectory along the orange path and finally escapes capture along the red path to the upper right. The size of Earth and the Moon are not to scale but the size of the minimoon’s path is to scale in the Earth-Moon system.

How many moons does the Earth have? If you guessed one, you're off--by a factor of a thousand. New research shows that the Earth's gravity sometimes snares asteroids--and that these space rocks orbit the planet as "mini-moons."

“Mini-moons are scientifically extremely interesting,” Dr. Robert Jedicke of the University of Hawaii at Manoa said in a written statement released in conjunction with a new study published in the March issue of Icarus. “A mini-moon could someday be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our solar system over 4.6 billion years ago.”

Jedicke, along with Jeremie Vaubaillon of the Paris Observatory, and Mikael Granvik of the University of Helsinki, used the Jade supercomputer at the National Computer Center for Higher Education in France to replicate the voyage of about 10 million asteroids that passed by Earth. The team then tracked the route of the 18,000 objects that subsequently were captured by Earth’s gravity.

“This was one of the largest and longest computations I’ve ever done,” Vaubaillon said in the statement. “If you were to try to do this on your home computer, it would take about six years.”

At any given time, Jedicke told National Geographic, "We estimate that there are one or two washing machine-size mini-moons and about a thousand larger than a softball [orbiting Earth]."

Jedicke spoke with NPR about his research in a story that hit airwaves Tuesday morning. Click here to listen to it online.

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