For centuries, Earth's Moon has remained one of the most fascinating objects in our solar system.
There are many moons in our solar system. But there is only one Moon.
For centuries, it dominated our night sky, outshining the planets that seemed to dance magically against the background of stars. It was such a constant - as constant as Earth itself - that it didn't need a name. It was simply the Moon in the many languages of Earth..
Things got more complicated about four hundred years ago when Galileo Galilei discovered four moons orbiting Jupiter. The dozens of natural satellites discovered since get exotic names: Europa, Portia, Io and Hydra, etc. Our Moon keeps it simple.
Throughout history, our Moon has been a constant source of fascination. Ancient civilizations worshipped it and used it to measure time. The introduction of the telescope in 1609 enabled observers such as Galileo to observe the spots were shadows of mountains and valleys that made the Moon less of a heavenly body and a little more like Earth.
As telescopes improved, so did the view. Then, fifty years ago, space travel changed everything.
The Moon also was a prime target for early spacecraft. Robotic spacecraft photographed and smashed into the Moon's dusty, battered surface before making the first landings that paved the way for 12 human beings to walk on its surface during the historic Apollo missions of the late 1960s and early 1970s.
More than 70 spacecraft have visited the Moon. Among the robotic visitors: the Jupiter-bound orbiter named in Galileo's honor. Scientists tested its instruments with Moon observations before as it made its historic journey to study Jupiter and Galileo's other great discovery, the Galilean satellites.
We still have a lot to learn from the Moon.
Plans are currently underway to send astronauts back to the Moon as part of a larger strategy to see how far humanity can safely venture into our solar system.
Current goals call for astronauts to return to the Moon by 2020.
Just as they did in the Apollo era, robotic missions lay the groundwork for human explorers who can refine the art and science of living outside Earth's protective atmosphere.
NASA's unmanned Lunar Reconnaissance Orbiter is taking the first steps by searching for deposits of water-ice that prospective Moon colonists could use to make air, fuel and perhaps to grow food. The spacecraft will travel to the Moon with Lunar Crater Observation and Sensing Satellite (LCROSS), which will impact in a permanently shadowed crater on the lunar South Pole in the hopes of sending up a plume that can be scanned for signs of water.
Other spacecraft will chart valuable mineral deposits that could build future spacecraft that could venture into space without battling Earth's gravity and atmosphere.
The Moon not only holds possibilities for humanity's future. It also contains important clues to our past.
The Moon's South Pole-Aitken Basin is one of the largest known impact structures in our solar system. The impact-by a comet or asteroid - stripped away much of the Moon's crust and upper mantle, possibly provide access to materials dating back to the formation of the Earth and Moon.
Similar materials on Earth and other planets have been buried by centuries of geologic activity.
Aitken Basin rocks and soil samples could contain information about the period of heavy bombardment that likely affected the emergence of life on Earth and other worlds. During that period from about 4.5 to 3.8 billion years ago, asteroid-sized objects hit Earth, the Moon and other planets almost daily.
Mission proposals call for a robotic spacecraft to collect samples from the Aitken Basin and rocket them back to Earth in a sample container.
After the American Apollo missions, the Soviet Union collected its own lunar soil samples with the unmanned Luna 16 spacecraft and sent them back to Earth in 1970. It was the first successful robotic sample return from space.
A sample return from the Aitken Basin would determine if there is sufficient hydrogen - and possibly water - and other volatiles to sustain human explorers.
Last Updated: 2 February 2011