Lunar Love: New Calculation Shows Moon's Heart is All Mushy By SPACE.com Staff posted: 07:56 am ET 14 February 2002 How Far the Moon? We'll Know in One Year Study of Lunar Soil Confirms Moon's Origins The Moon Or Mars…Which Shall It Be? 24 Hours of Chaos: The Day The Moon Was Made Augustus E.H. Love was an Oxford mathematician who worked on mathematical theories of elasticity and waves in the late 1800s and early 1900s. Now, on Valentine's Day, Love's name has been given to a new measurement of the Moon, a favorite sight for swooners. No Kidding Did you know that there are 400 trees on Earth that came from the Moon? Or that the Moon is moving away from us as you read this? Scientists have generated a new calculation of how the Moon's surface and interior move in response to the gravitational pull of the Earth and the Sun. The math shows that the Moon bulges out by as much as 10 centimeters (4 inches) during the roughly 27 days it takes to orbit Earth. Love numbers show how elastic the Moon is, giving clues to the material under the surface. The new number supports a 30-year-old idea that a partially melted zone lies above the core. The heart of the Moon, like many hearts, may be mush, or rather something like a molten slush surrounding a solid core. "Since we can't go inside the Moon, we have to use indirect methods to learn its hidden secrets, said James Williams, a research scientist at NASA's Jet Propulsion Laboratory. "In this case we were able to use the tidal distortion of the Moon." Williams and his colleagues will present their findings at the annual Lunar and Planetary Science conference next month in Texas. The Love number tells how the Moon's gravity field changes as it changes position in relations to the Earth and Sun. The Moon's Love number is 0.0266. Earth's is 0.3, showing that our planet's bigger, rocky surface may move as much as a half a meter (about 20 inches) in a day in response to the pull of the Moon and Sun. Venus' surface, with a Love number of .3, may move as much as .4 meter (about 1 foot) from the pull of the Sun. The lunar numbers were not a surprise. NASA's Apollo missions found that moonquake waves lost energy if they went deeper than 1,000 kilometers (620 miles), or over halfway into the center of the Moon. This might mean that the Moon's depths are at least partially melted, Williams said. After the Apollo measurements of moonquakes ended in 1977, two decades passed without new measurements of the deep lunar interior. Researchers calculated the Love numbers from data gathered by the Lunar Laser Ranging Experiment, using retroreflectors left on the Moon's surface 30 years ago by U.S. and Russian missions. A laser pulse is fired from Earth to the Moon, bounced by a reflector and returned back to Earth. The round-trip travel time gives the distance between the two bodies with accuracy better than 2 centimeters (.8 inches). Scientists who analyze the data from the Lunar Laser Ranging Experiment have measured, among other things, that the Moon is moving away from Earth and that the shape of Earth is changing. The Moon's composition has always been something of a mystery. It contains very little iron. Earth, on the other hand, is loaded with iron, the bulk of which is in the planet's core. Scientists think this shows that the Moon was created in a violent collision, when a Mars-sized object slammed into Earth. The Moon was then formed from iron-poor material that came from the outer layers of Earth and colliding object.
