MAX MASON ReutersUP AND AWAY: the ‘two moon’ theory is one of the many mysteries NASA’s new solar powered twin lunar laboratory will attempt to solve.
Imagine looking up into the night sky, there are no clouds, the stars are shining and the glow of two moons radiates down to earth.
the “two moon” theory introduced by Martin Jutzi and Erik Asphaug of the University of California at Santa Cruz is just one of the many mysteries NASA’s solar powered twin lunar Gravity Recovery and Interior Laboratory (GRAIL) – which launched from Cape Canaveral on Saturday at 11:08pm (EST) – will attempt to solve.
It is widely accepted by scientists that about 4 billion years ago, a large planet sized object collided with Earth. the resulting debris is thought to have formed the moon, or moons, according to the new theory.
Talking to Fairfax Media, MIT research scientist and deputy principal investigator for the GRAIL Discovery Mission, Dr David E Smith, explained that by studying the moon, the “two moon” theory and a host of other mysteries about planet formation could be better understood.
“At the top level the objectives [of GRAIL] are to improve our knowledge of the interior of the moon from ‘crust to core’; to advance understanding of the thermal evolution of the moon (how it cooled); and also to extend this knowledge of the moon to the other terrestrial planets (Mars, Earth, Venus, and Mercury),” he said.
all these planets went through the same early formation process at about the same time and suffered the same bombardment that we can see on the lunar surface and on Mercury, but it is not evident on the Earth or on Venus.
“For some reason those bodies evolved differently in the subsequent 3 to 4 billion years,” said Dr Smith.
GRAIL will measure the gravity field of the moon by recording the distance between the two spacecraft to about a micron (a human hair is 40 to 120 microns in diameter).
“As the spacecraft move over the surface features on the moon the distance between the two spacecraft will change as a result of the attraction of material on and in the moon, thus providing the acceleration of gravity everywhere over the lunar surface,” said Dr Smith. “The variation in the gravity measurement is a measure of the variation in density within the moon.”
Dr Smith said by understanding the composition of the moon, scientists will be able to infer the internal structure which will allow them to make more accurate assumptions on how structures such as basins and craters were formed.
It is here that the “two moon” theory could be explained. While the side of the moon facing Earth is relatively smooth, the dark side has what is known as the lunar highlands, full of uneven and mountainous formations.
the theory suggests that the second moon, suggested to be 1/3 of the size of the moon, collided with the lunar surface, resulting in the vast surface differences found between the two sides of the moon.
In the science journal Nature, deputy principal investigator for the GRAIL, Maria Zuber, suggested that the detail obtained by GRAIL and Lunar Reconnaissance Orbiter will allow for more accurate simulations to prove or disprove the “two moon” theory, but ultimately a sample of materials would be needed.
If the “two moon” theory is correct, the age of the materials on either side of the moon will be different.
GRAIL’s two spacecrafts will be sent into the orbit of the moon on New Years Eve and New Years Day respectively and the team at NASA and MIT are excited about the months to come.
“We are delighted that GRAIL is on its way, and a great relief that the ‘dangerous’ part is over,” said Dr Smith. “Space is a more benign environment that Earth.”
– Sydney Morning Herald
May 10, 2011 08:00 AM Eastern Daylight Time 
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