Earth has more than one Moon, scientists say

Earth has more than one Moon, scientists say

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News & Events - Engineering News

April 11, 2012

The conventional notion that the Earth has only one Moon is not necessarily true, according to scientists.

NPR reports that the results of a new study conducted by an international team of scientists found that at any given time, there is more than one object orbiting the Earth. According to Robert Kedicke, an astronomer at the University of Hawaii's Institute for Astronomy, the number of 'moons' orbiting the planet is constantly changing.

"At any time, there are one or two 1-meter diameter asteroids in orbit around the Earth," she said.

The team of researchers, armed with advanced engineering research tools, said that it was exceedingly difficult to detect these transient objects. Jedicke said that scientists instead had to focus on information they did know as they worked to ascertain how many pieces of space debris shared the same orbital path as the Earth.

"We know that there is a population of asteroids in orbit around the sun, that can come close to the Earth at some point in their orbit," he said. "But there's a very small subcomponent of that population that are on orbits that are very much like the Earth's."

The scientists found in their work that as some objects soar past Earth, there is a chance they can be trapped in its gravitational pull. According to Jedicke, approximately 1 million pieces of space debris pass close by the Earth each year. Jedicke and his colleagues at the University of Finland and the Observatoire de Paris developed a computer program that would help gauge the number of objects that are trapped in Earth's gravitational pull as they pass by the planet.

The scientists said that a majority of the asteroids and other space rocks that get enveloped in the gravitational pull of Earth are likely small, measuring no longer than 3 feet across. However, they said that occasionally some objects that are much larger in size are also caught in Earth's orbit.

"Maybe once every 100,000 years, there'll be an asteroid that's about the size of a football field in orbit around the Earth," Jedicke remarked.

At that size, an asteroid is so large that even casual stargazers can view it. Still, the scientists said that even though the Earth's gravitational pull is strong enough to capture objects so large in size, they do not remain entrapped for an extended period of time. That, according to Jedicke, is because when they are indeed captured, it is "so loose that little gravitational nudges from the other planets in the Solar System or from the Moon can eventually just sort of dislodge them from the Earth's gravity and allow them to go back into orbit."

NASA Jet Propulsion Laboratory scientist Paul Chodas said the space agency routinely monitors the asteroids that lurk in the Solar System. He added that when researchers in Pasadena identified a small object orbiting the planet recently, they did not realize it was an asteroid – at first.

"There was one very small asteroid which was discovered to be in orbit around the Earth. We didn't know that right away," he said. "We thought it might be an old rocket stage or some other junk left over from the space program. But the trajectory indicated it was an asteroid."

In total, the scientists estimated that as many as 1,000 unseen objects could be orbiting the planet at any time, according to National Geographic. The researchers published their findings in the journal Icarus.


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