24 January 2012

When did the earth have two moons?

The last time was in the autumn of 2006.  But after orbiting the earth for less than a year, it departed.  Details via PhysOrg:
Temporary satellites are a result of the gravitational pull of Earth and the Moon. Both bodies pull on one another and also pull on anything else in nearby space. The most common objects that get pulled in by the Earth-Moon system’s gravity are near Earth objects (NEOs) — comets and asteroids are nudged by the outer planets and end up in orbits that bring them into Earth’s neighbourhood...

They found that the Earth-Moon system captures NEOs quite frequently. “At any given time, there should be at least one natural Earth satellite of 1-meter diameter orbiting the Earth,” the team said. These NEOs orbit the Earth for about ten months, enough time to make about three orbits, before leaving.
One implication is that the study of the cosmos can be facilitated by visiting/sampling these temporary moons rather than trying to access more distant bodies.

1 comment:

  1. Seems unlikely that the earth has ever had just two moons. Right now. The US Space Surveillance Network (SSN) is currently tracking ~8,000 objects of 10cm or greater diameter in orbit about the earth. About seven percent are operational satellites (i.e. ~560 satellites).


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