Did Earth Once Have Multiple Moons?

Moons_whatmough_020924_01_2The history of planet Earth is a fascinating story, involving catastrophic collisions with other small planets and a veritable plethora of asteroid impacts. The prevailing theory about the formation of the moon is called the giant impact hypothesis: the theory goes that a Mars-sized object, known as Theia, crashed in to the young Earth. What was left was Earth, and its moon.

In his new book, What if the Earth had Two Moons? Neil Comins investigates this possibility, along with nine other tweaks that might make our cosmic neighbourhood subtly – or fundamentally – different. What if the moon orbited Earth backwards? What if our solar system were located in the centre of our galaxy, rather than in a remote region of an outer arm?

Elsewhere, a computer model suggests that the Moon may not have been the only reminder of that big collision. Jack J. Lissauera of the Space Science and Astrobiology Division, NASA Ames Research Center, and John E. Chambers of the Department of Terrestrial Magnetism, Carnegie Institution of Washington, have suggested that moonlets called Trojans may have been left behind in the collision.

"The giant impact that likely led to the formation of the Moon launched a lot of material into Earth orbit, and some could well have been caught in the Langrangian points," -points in space where the gravity between two objects cancels the other out, said says study team member Lissauer.   Their theory places small moonlets, or Trojans, in Earth’s orbit, for up to 100 million years.

Over time, gravitational tugs from other planets would have eventually altered Earth’s orbit, even if it was only slightly. Thus, the Langrangian points would have altered, leaving the Trojans once again susceptible to gravity. From there, they could be anywhere by now, or destroyed entirely.

"The perturbations from the other planets are very, very tiny," said Lissauer. But they change the shape of Earth's orbit, which subsequently changes the effect that the Sun's gravity has on the moons, that "…is what ultimately destabilizes the Trojans."

A separate yet similar model created by Matija Cuk, an astrophysicist at the University of British Columbia in Canada has suggested that smaller, asteroid sized objects, only a few tens of kilometers in width, could have lasted longest in those stationary positions. She believes that they could have lasted a lot longer too, up to a billion years or more.

However she noted that “they would have looked more like Jupiter or Venus in the sky than a satellite. They would have resembled very bright stars.”

Posted by Josh Hill.

Related Galaxy posts:

21st-Century Map of the Moon's South Pole
MIT Moonbase to Search for 'Dark Age' of the Universe
Our Lunar Moon -A Rarity in the Cosmos
Japan's SELENE Captures Earth Rise at the Lunar North Pole
Moon-Base Architects Plan 1st Step in Exploring the Cosmos –A Daily Galaxy Interview

Links:

http://space.newscientist.com/article/dn13836-did-earth-once-have-multiple-moons.html?feedId=online-news_rss20

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