Science/AAAS
This graphic (not to scale) shows that the moon's crust is thickest on the central far side, and becomes thinner towards the north pole in a manner described with a simple math formula. The highlands appear to have formed early in the moon's history, when a magma ocean, shaped by tides caused by Earth's gravity, heated the moon's floating crust non-uniformly. Since then, the magma ocean has solidified.
updated 11/11/2010 4:02:02 PM ET 2010-11-11T21:02:02

The far side of the moon is forever hidden from the naked eye on Earth, but now scientists have developed a simple way to describe how it looks, and in doing so could shed light on its enigmatic history.

The simple mathematical formula they devised "explains at least a quarter of the moon's geography and geology," including the lunar far side's highlands, Ian Garrick-Bethell, a lunar scientist at the University of California, Santa Cruz, said. [ Graphic: The moon's far side explained ]

The near and far sides of the moon are very different for instance, elevations on the far side are some 1.2 miles (1.9 km) higher, on average and understanding the roots of those differences could shed light on the mysterious early days of the moon.

Far side of the moon
The moon always keeps the same side turned toward Earth, which means one cannot see its far side often erroneously referred to as its "dark side" from Earth's surface. Humanity saw its first pictures of the far side of the moon in 1959 from unmanned probes, and human eyes first directly observed it during the Apollo 8 mission in 1968.

Researchers discovered the formula while analyzing sets of lunar topography and gravity data, Garrick-Bethell told SPACE.com.

The stretch of the moon's far side surface explained by the new formula has to be the oldest lunar feature seen yet, since it lies beneath the ancient South Pole-Aitken Basin. The mathematics of it is similar to what applies to Jupiter's tidal effects on its moon Europa.

"Europa is in many ways different from the moon, but early on, the moon had a liquid ocean under its crust, and it likely shares that in common with present-day Europa," Garrick-Bethell said. "The ocean for the moon was of liquid rock, however, not water."

Moon's magma ocean
Just as the moon tugs on Earth's oceans, generating tides, so does Earth pull at the moon.  The researchers suggest that roughly 4.4 billion years ago, when the moon was less than 100 million years old and its crust floated on an ocean of molten rock, these tidal effects caused distortions that were later frozen in place.

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"People have been thinking about tidal explanations for the large-scale structure and shape of the moon for at least 100 years," Garrick-Bethell said. "The new thing here was to look at only one specific region of the moon that is very old, rather than to test the hypothesis over the moon as a whole, which was done previously.

"As a whole, the moon exhibits a wide range of geologic processes, some young and some old, so I don't think it's fair to explore it as a whole."

These findings yield insight into the fundamental processes that built the lunar crust, Garrick-Bethell said.

"I would like to map out how this terrain may actually extend to other parts of the moon, and encompass even more surface area than we initially report," he added.

The scientists detail their findings in tomorrows (Nov. 12) issue of the journal Science.

### Photos: 50 years of views from the moon

1. Up-close exploration of the moon, Earth's only natural satellite, began in 1959 when the Soviet Union launched its Luna 1 spacecraft on a flyby mission. NASA quickly followed up with missions of its own. Since then, the Europeans, Japan, China and India have launched their own lunar exploration programs. This view shows the moon as seen from the international space station. Click the "Next" arrow above to check out 11 images from the moon made over the last 50 years. (NASA) Back to slideshow navigation
2. #### 1959: Far side in full view

In October 1959, the Soviet Union's Luna 3 spacecraft - the third successfully launched to the moon - made history as the first probe to image the far side of the moon. The photos were fixed and dried on the spacecraft and beamed back to Earth. Though fuzzy by today's standards, the images showed stark differences from the near side, including relatively few dark areas, called lunar maria. (RSA via NASA) Back to slideshow navigation
3. #### 1966: A restored ‘Earthrise'

In 1966 and 1967, NASA sent a series of Lunar Orbiter spacecraft to collect detailed images of moon's surface in preparation for the Apollo program. The tapes were then put in storage. Decades later, researchers with the Lunar Orbiter Image Recovery Project collected the vintage hardware required to play back the imagery. That imagery was digitized , reproducing the images at a much higher resolution than previously possible. On Nov. 11, 2008, the project researchers released this enhanced photograph of Earth rising above the lunar surface, originally made by Lunar Orbiter 1 in 1966. (LOIRP / NASA) Back to slideshow navigation
4. #### 1968: The most famous 'Earthrise'

On Christmas Eve 1968, Apollo 8 astronauts Frank Borman, Jim Lovell and William Anders made history as the first humans to orbit the moon. They were scouting its surface for a suitable landing spot for future missions. But the sight of Earth rising above the moon's horizon caught their - and the world's - attention. The photograph, called "Earthrise," is among the most famous ever made from the moon. (NASA) Back to slideshow navigation
5. #### 1969: One small step

On July 20, 1969, an estimated 1 billion people around the world were glued to television screens to watch astronaut Neil Armstrong, commander of Apollo 11, climb down from the lunar module spacecraft for a stroll on the moon. As his foot touched the lunar surface, he famously said "That's one small step for (a) man, one giant leap for mankind." This image is a black-and-white reproduction from the telecast, showing Armstrong stepping down from the lunar module's ladder. (NASA Johnson Space Center) Back to slideshow navigation
6. #### 1969: Man on the moon

Apollo 11 astronaut Buzz Aldrin, shown here, accompanied Armstrong for the famous walk on the moon. This iconic image is one of the few that shows Armstrong on the lunar surface - as seen in the reflection on the spacesuit's visor. The astronauts walked around on the lunar surface for about two and a half hours. (NASA) Back to slideshow navigation
7. #### 1994: Looking for ice

This mosaic image of the moon's southern polar region, made by the Clementine spacecraft in 1994, suggested that the region could harbor water ice within regions of its craters that are never lit by the sun. The water ice would be left over from impacting comets. Scientists have debated the evidence for and against water ice at the poles ever since the Clementine discovery. The current era of lunar exploration could resolve the debate. If water ice exists, it could help quench the thirst of future human colonists and be used to make fuel for rockets. (NASA / JPL / USGS) Back to slideshow navigation
8. #### 2006: European moon probe crashes

On Sept. 3, 2006, the European Space Agency's SMART-1 spacecraft went out with a bang - a planned crash landing into a volcanic plain called the Lake of Excellence. The impact, shown here, was captured by the Canada-France-Hawaii Telescope. (The black lines are a processing error due to the brightness of the event.) The spacecraft was launched in 2003 primarily to test an ion propulsion system, which uses energy captured by the sun to produce a stream of charged particles. The slow-and-steady propulsion system may be used on future interplanetary missions. (Christian Veillet / CFHT via AP) Back to slideshow navigation
9. #### 2007: China targets the moon

China made its first major strides in the lunar exploration game with the launch of the Chang'e 1 spacecraft in October 2007. The orbiter was sent to make a detailed, 3-D map of the moon's surface. Premier Wen Jiabao unveiled the first image at a ceremony in Beijing, shown here. Chang'e 1's 16-month mission ended with a controlled crash. The country reportedly plans to launch lunar rovers in 2010 and 2017, and a manned mission to the moon by 2020. (Huang Jingwen / XINHUA NEWS AGENCY) Back to slideshow navigation
10. #### 2008: India joins the lunar club

The Indian Space Research Organization successfully launched its Chandrayaan 1 spacecraft on Oct. 22, 2008, for a mapping mission to the moon. A probe released from the mothership took this picture of the lunar surface during its descent to a planned crash landing at the south pole. The Indian space agency plans to use this and other data for a lunar rover mission in 2011 and, eventually, a manned mission. (ISRO via EPA) Back to slideshow navigation
11. #### 2009: Japan orbiter watches eclipse

Some eclipse enthusiasts travel the globe to glimpse alignments of the sun, Earth and moon. Japan's Kaguya probe did them one better: It shot this sequence of a Feb. 10, 2009, eclipse from its lunar orbit. The image shows the view of the sun from the moon mostly covered by Earth. The "ring" appears dark at the bottom because it is obscured by the night-darkened limb of the moon. The Kaguya orbiter was launched in September 2007 to study the moon's origin and evolution. It made a controlled crash landing on the moon in June 2009. (JAXA / NHK) Back to slideshow navigation
12. #### 2009: NASA goes back to the moon

On June 18, 2009, NASA launched two spacecraft to the moon to map its surface in unprecedented detail, scout for future landing sites, and smash probes into a permanently shaded crater in hopes of resolving a longstanding debate over whether such regions contain water ice. NASA's Lunar Reconnaissance Orbiter will orbit both poles for a year, and its mission could be extended to serve as a communications relay for future lunar missions. This is one of the first pictures sent back by the orbiter. LRO's sibling, the crater-smacking LCROSS probe, is due to impact the moon's south pole in October. (NASA / GSFC / ASU) Back to slideshow navigation
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