Did Earth once have two moons?

Earth must have felt pretty inadequate a week or two ago when astronomers announced that distant Pluto has yet another moon. Pluto! Recently demoted to a dwarf planet! And yet it boosted its satellite total to four, while we remain forever stuck at one. True, Earth is ahead of Mercury and Venus, which have no moons at all. But Mars, which is significantly smaller than Earth, has two; and don’t even mention Jupiter, with more than 60; or Saturn, with 53. Even asteroids have multiple moons — including Sylvia, a 384-mile (617 km) space rock that boasts the twin satellites Romulus and Remus.

But Earth’s rep may might gotten a bump, thanks to a paper just published in the journal Nature. Our home planet may have just one lonely moon now, but long ago, like Mars and Sylvia, we had two. “Whether it’s right or not, I don’t know,” says Maria Zuber, a planetary scientist at MIT who wrote an opinion piece accompanying the new study. “But I think it’s very plausible.”

The idea, cooked up by astronomers Martin Jutzi and Erik Asphaug, of the University of California at Santa Cruz, started out as an attempt to explain why our moon has so asymmetrical a surface. The part that faces us is relatively smooth, with vast expanses of ancient lava forming flat, dark, low-lying plains that earlier astronomers mistook for oceans. But when space probes first circled the moon in the early 1960s, scientists learned that the far side is mostly covered with rugged mountains and craters.

Full Article on Time.com

Scientists Think Earth Once Had 2 Moons

by Jessica Berman

A new theory by planetary scientists says the Earth may once have been orbited by two moons, which formed early in the history of the solar system and collided slowly into one another to form a single Moon.

Collision course

Scientists believe the Moon was formed when a Mars-sized object crashed into Earth some 4.5 billion years ago and the debris accreted, or came together to form the Moon.

But to Erik Asphaug a planetary scientist at the University of California Santa Cruz, that does not address what astronomers call the lunar dichotomy between the visible side of the moon, marked by craters and a thin crust, and the far side of the moon, known to contain a thicker crust and mountain ranges topping 3,000 meters.

Scientists think Earth once had two moons, Voice of America

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