New Insights Into the Birth of Our Satellite

Moon Blast! New insights into the birth of our satellite By: Leon Jaroff Time Magazine August 27, 2001

The day, some 4.5 billion years ago, was just five hours long, but it was a momentous one for Earth. A Mars-sized object roaring in at 25,000 mph struck the young planet, already largely formed but devoid of life. The glancing blow hurled molten and vaporized debris into space, where it cooled began circling Earth and eventually coalesced to form the moon.

This scenario is draw from a new computer simulation that goes far toward resolving puzzling inconsistencies in earlier students of the moon’s formation. That event was, of course, of overwhelming importance in our planet’s history since it reduced Earth’s rotational wobble and set the stage for ocean tides, and ultimately life. Earlier simulations required a much larger object crashing into an Earth only partly formed and spinning too fast to explain Earth’s current rotational rate – our 24 hour day. One study needed to separate impacts to scale back the spin rate.

To get at these ancient events, Robin Canup of the Southwest Research Institute in Boulder, Colorado, and Erik Asphaug of the University of California at Santa Cruz reenacted them in their computers by taking into account such factors as gravity, impact shock, melting, and vaporization. They also created models with a finer level of detail than previous efforts. Finally, after a number of tries, they arrived at a scenario in which an object, the size of Mars, but only one-tenth of Earth’s mass, sticking at a highly oblique angle, ejected enough debris from itself and our planet’s iron-deficient out layers to form the moon, which contains very little iron. Left behind was an earth that was roughly the size it is today.

Apart from satisfying our curiosity about how the moon was formed, the new work has broader implications. Explains Asphuag, “It’s now known that giant collisions are a common aspect of planet formation, and these big impacts might go a long way toward explaining the puzzling diversity among planets.” The diversity was emphasized last week when astronomers using the University of California’s Lick telescope reported the discovery of two planets orbiting around a distant star. Unlike all previously discovered extra-solar planets, which have highly elliptical orbits, these two were moving in nearly circular paths. Alas, even the best telescopes are not sensitive enough to detect any extra- solar moons.

Moon blast assignment (15 points) After reading the article, pick out 6 of the most important points that explain how the moon was formed.

Take those 6 most important points and make a 6 panel cartoon. You must include drawings (in color) and include a caption (tell us what is happening) for each panel.