Preparing For A Walk On The Moon

Astronomers Discover That The Earth's Magnetotail Charges The Surface Of The Moon

October 1, 2008 — Astrophysicists found that the moon's surface becomes electrified during each full moon. The moon passes through the Earth's magnetotail, a cone of highly-charged particles, for about 6 days each month. On the side of the moon facing the sun, ultraviolet particles disrupt the electromagnetic effect, keeping the voltage at low levels, but on the dark side, the voltage can reach hundreds or thousands of volts.

The last time man walked on the moon was in 1972. Now, NASA is planning to re-visit the moon by the year 2020 -- but a shocking discovery about Earth's companion may put a hold on those plans.

Our moon looks calm and rather dull, and nothing ever seems to change. Even an astronaut's footprint lasts millions of years; but now, space scientists have learned something on the moon does change -- and it's quite shocking.

"The surface of the moon can become electrified from charged particles in the surrounding space environment," says Timothy Stubbs, Ph.D., a space scientist at the NASA Goddard Space Flight Center in Greenbelt, Md.

This electric event happens once a month when the moon passes through the earth's magnetotail. A magnetotail is caused when the highly-charged particles of the solar wind zoom past the earth and mix with earth's magnetic field, creating a long tail that extends into the moon's orbit. "The moon is actually sitting in a sea of charged particles," Dr. Stubbs says.

Each month, the moon enters the magnetotail for six days. As it crosses inside the magnetotail, the moon's surface becomes highly charged. If astronauts walked across the charged surface, they might feel a static shock -- just like walking across a carpet and then touching a door knob. It's not a deadly shock, but a powerful zap! It's easy to know when the moon is passing through the earth's magnetotail -- just look for a full moon.

No astronaut has ever landed on a charged-up full moon to know exactly what happens, so learning more now will help astronauts in the future.

"These sorts of things that affect astronauts are things that we'd like to investigate before we return to the moon," Dr. Stubbs says.

When NASA returns to the moon, scientists plan to establish an outpost for long-term moon exploration -- and they plan to also explore the magnetotail.

ABOUT THE MOON: The moon is Earth's only natural satellite, a cold, dry orb whose surface is studded with craters and strewn with rocks and dust. The moon's gravitational force is only 17% of the Earth's gravity. For example, a 100 pound (45 kg) person would weigh just 17 pounds (7.6 kg) on the Moon. The temperature on the Moon ranges from daytime highs of about 265F (130C) to nighttime lows of about -170F (-110C). The moon has no atmosphere. On the moon, the sky always appears dark, even on the bright side (because there is no atmosphere). Also, since sound waves travel through air, the moon is silent; there can be no sound transmission on the moon. The phases of the moon are caused by the relative positions of the earth, sun, and moon. The moon goes around the earth, on average, in 27 days, 7 hours, and 43 minutes. The sun always illuminates the half of the moon facing the sun (except during lunar eclipses, when the moon passes through the earth's shadow). When the sun and moon are on opposite sides of the earth, the moon appears "full" to us, a bright, round disk. When the moon is between the earth and the sun, it appears dark, a "new" moon. In between, the moon's illuminated surface appears to grow (wax) to full, then decreases (wane) to the next new moon.

WHAT IS THE SOLAR WIND? Flowing outward from the Sun's extremely hot corona, the solar wind is a stream of charged particles traveling in all directions at incredibly high speeds. As these changes speed toward the Earth, they interact with other charged particles and can create phenomena such as the northern lights and geomagnetic storms -- which can damage spacecraft, including communications satellites.