Sunday, October 18, 2009

The Moon

Most people heard that NASA launched a missile at the moon's south pole last week, followed by the LCROSS spacecraft. The experiment was designed to search for the presence of underground glacial water, which scientists have suspected might be found beneath the Cabeus A crater. The LCROSS spacecraft flew into the plume of dust left by the missile's impact and measured the properties before also colliding with the lunar surface.

The experiment cost $79 billion, cheap in the world of space travel. Millions gathered outside with binoculars and telescopes on the early morning of September 9 to observe the impact. It therefore seems like a good time to post a few comments on the moon, our nearest celestial neighbor, and the only body with details visible without a telescope.

As far as we can tell, it's unusual for a satellite and its host planet to be so close in size as the Earth is to the Moon. Mercury and Venus have no moons, and Mars has two, but they are very tiny. The diameter of our moon is about one-fourth that of Earth (3480 Km, 2160 mi.); but its volume is one-fiftieth of Earth's, and the Earth's mass is 81 times greater than the mass of the moon. Thus the pull of gravity on the lunar surface is only one-sixth of what it is here.

A rocket trip to the moon takes 60-70 hours. If you drove to the moon by car at a steady speed of 75 miles per hour, it would take 135 days to reach your destination. Twelve men and no women have walked on the moon, and the Apollo missions have collected 842 pounds of moon rocks.

Although the strength of the moon's gravity is one-sixth that of Earth's, the gravitational field itself is uneven. There are patches of unexpectedly high gravity , called "mascons", or "mass concentrations" on the lunar surface. Nobody knows for certain what causes them, but they are found in high concentrations where there are thick layers of lava from volcanic activity. Surprisingly, not all areas which were once volcanically active host mascons.

In 2011, NASA will send a probe to study the moon's gravity in minute detail. This will not only allow us to learn more about the moon, but also about how gravity can work here on Earth, and throughout the universe.

Things hardly ever change on the surface of the moon. Neil Armstrong's footprint will be visible for thousands of years, and it is still possible to find rocks on the surface from when the Solar System was created. The astronauts from the Apollo 15 mission found a rock that is 4.5 billion years old. Called the Genesis Rock, it is now on display at the Johnson Space Center in Houston, Texas.

The moon is a very quiet, stable environment, which makes it a terrific place to mount astronomical instruments. In fact, the moon is a perfect observatory, completely free from noise, light, and atmospheric interference such as we have here on Earth.

Some day its craters might be used as dishes for massive radio antennae. It's also an ideal launch pad for deep space exploration. If bases could be established on the moon, deep space exploration would become much easier. To exploit this potential, first we'd need to work out how to live there and build construction facilities. This is where water, native to the moon rather than shipped from Earth, would come in handy. Then we would have to find a way to launch space vehicles in a lunar environment.

No doubt it's a big job, but we're working out the details all the time.

For more information, I recommend checking out the Book of the Moon, by Rick Stroud.

For my previous posts on outer space, click here.

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