Could the Moon have its own moon?

I was reading the “Science & Vie” magazine when I came across a question from one of the readers: “Does the Moon have satellites?”  At first I considered this quite a silly question, but then realized that we have placed artificial satellites around the Moon.  So why could there not be natural ones?

The Moon is not billiard-ball smooth gravitationally.  It’s heavily scared surface due to past asteroid and comet impacts have affected the local density of the surface crust, and therefore the local gravity field varies across the surface of the Moon.

Map of gravity acceleration values over the entire surface of Earth's Moon.  Lunar Gravity Model 2011

Map of gravity acceleration values over the entire surface of Earth’s Moon. Lunar Gravity Model 2011

One of the famous effects of these local gravitational variations is the Apollo 11 landing, where Neil Armstrong had to take manual control to land, some 5km down range where the navigational computer was targeting.

Another factor is that any satellite around the Moon would also be under the influence of the Earth and the Sun.  Any asteroid captured by the Moon would quickly be ejected due to all these influences.  Now there are more favorable orbital angles: 27, 50, 76 and 86 degrees from the Moon’s equator.  But it would still be a highly unstable orbit.  All spacecraft that are placed in orbit around the Moon need to use up propellant to maintain orbit over time.  And when propellant is about to run out, most space agencies elect to purposely crash the satellite to obtain additional science data.  One recent example is NASA’s LADEE moon orbiter crashing on the Moon on April 18th, 2014.

In conclusion, no our Moon does not have any natural satellites, and if by chance it would capture a wandering asteroid, most experts believe it would only survive a century at most before impacting the lunar surface or getting flung out of orbit.

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