Earth's moon shaped by impact with another: study

LOS ANGELES Thu Aug 4, 2011 9:03am EDT

Four snapshots from the computer simulation of a collision between the moon and a smaller companion moon show most of the companion moon is accreted as a pancake-shaped layer, forming a mountainous region on one side of the moon. REUTERS/M. Jutzi and E. Asphaug, Nature/University of California Santa Cruz

Four snapshots from the computer simulation of a collision between the moon and a smaller companion moon show most of the companion moon is accreted as a pancake-shaped layer, forming a mountainous region on one side of the moon.

Credit: Reuters/M. Jutzi and E. Asphaug, Nature/University of California Santa Cruz

Related Topics

LOS ANGELES (Reuters) - A primordial collision of two moons that once orbited Earth explains why the present-day moon is a bit lopsided and its far side much rockier than the lunar surface facing our planet, scientists said Wednesday.

Research published in the journal Nature suggests the early moon was shadowed by a smaller companion satellite, about one-thirtieth of its own mass, as the two bodies circled the infant Earth in tandem more than 4 billion years ago.

But as the moons evolved further from the Earth, coming under greater influence of the Sun's gravitational force, the stability of their co-orbit was upset, putting them on a collision course, said Erik Asphaug, a planetary scientist at the University of California, Santa Cruz.

After about 100 million years of cohabitation, the smaller moon finally crashed into the larger moon in an impact that unfolded over several hours and resulted in a merger of the two celestial bodies, Asphaug said.

All this occurred just 80,000 miles from Earth, about a third of its current 250,000-mile distance from the moon.

The violent but slow-motion celestial union explains much about the striking difference between the mountainous far side of the moon and the smoother lunar surface of vast plains visible to Earth in the night sky, the scientists concluded.

Rather than form a giant crater, a low-velocity collision like the one theorized in the study would have piled material up into a thick, jagged layer of solid crust. In fact, the moon's crust is about 30 miles thicker on its far side than on its near side.

The lunar crash also accounts for an overall asymmetry of the moon -- bulging out more on its far side -- not easily explained by tidal forces exerted by the Earth.

Evidence of a collision exists further in variations in the composition of the moon's crust, the near side of which is far richer in potassium, rare-earth elements and phosphorus.

Those elements would have been concentrated in molten material still cooling beneath the moon's surface and splattered away to the opposite side by the force of the impact, Asphaug said.

The research builds on the widely accepted "giant impact" model for the origin of the moon. According to that theory, the moon was created from debris ejected by the last of a series of collisions between the primordial Earth and about 10 Mars-sized proto-planets during the early formation of the solar system.

The study suggests that moon-forming giant impact also created a smaller, companion body that eventually coalesced with the larger satellite to form today's single moon.

(Editing by Todd Eastham)

FILED UNDER:
We welcome comments that advance the story through relevant opinion, anecdotes, links and data. If you see a comment that you believe is irrelevant or inappropriate, you can flag it to our editors by using the report abuse links. Views expressed in the comments do not represent those of Reuters. For more information on our comment policy, see http://blogs.reuters.com/fulldisclosure/2010/09/27/toward-a-more-thoughtful-conversation-on-stories/
Comments (2)
Whittier5 wrote:
I trust no one thinks this is new news. This fact was known by several Mesopotamian cultures, Egyptian and, I believe, Hindu as well. I would think the Banana Slugs at UCSC would know this.

See “12th Planet” by Sitchin. Also, part of the moon was probably torn from the Pacific Basin by an asteroid or planet impact or “drive-by”.

Aug 04, 2011 11:34am EDT  --  Report as abuse
snap2 wrote:
This is built on the old theories of impacts and gravity rather than the plasma model of huge electric currents. Looking at NASA’s new Vesta images from yesterday it seems electrical machining is the cause of such a clean, pock-marked surface. Same for the moon. I urge you to watch youtube “The Lightning-Scarred Planet Mars” for an intro to this fascinating new idea! There is a lot of very convincing evidence when you start looking.

Aug 04, 2011 4:20pm EDT  --  Report as abuse
This discussion is now closed. We welcome comments on our articles for a limited period after their publication.