Rediscovered Apollo data gives clues to moon dust
Sen—More than 40 years after man first landed on the Moon, scientists have used rediscovered data from the Apollo program to make the first determination of how fast lunar dust accumulates.
Professor Brian O’Brien of the University of Western Australia, a physicist working on the Apollo program back in 1969, developed the Lunar Dust Detector to make the first measurement of lunar dust accumulation. Dust was collected on small solar cells attached to experiment packages left by the Apollo 12, 14 and 15 astronauts. As the matchbox-sized device’s three solar panels became covered by dust, the voltage they produced dropped.
The devices operated over the course of six years, until NASA shut them off in September 1977 due to budgetary concerns. NASA did not preserve the archival tapes of the data they collected. For three decades NASA assumed the dust detector data had been lost forever, until 2006 when O’Brien heard about NASA’s mistake and told them he still had a set of backup copies.
The Lunar Dust Detector, attached to the leftmost corner of this experiment package left by the Apollo 12 astronauts, made the first measurement of lunar dust accumulation. Image credit: NASA
Now, scientists have used the rediscovered data to measure how fast the lunar dust accumulates. The electrical measurements indicated that each year 100 micrograms of lunar dust collected per square centimetre. At that rate, a basketball court on the Moon would collect roughly 450 grams (1 pound) of lunar dust annually.
Forming a layer about a millimeter (0.04 inches) thick every 1,000 years is 10 times previous estimates. It’s also fast enough to pose a serious problem for the solar cells that serve as critical power sources for space exploration missions. That faster-than-expected pile-up also implies that lunar dust could have more ways to move around than previously thought.
Previous model-based estimates of lunar dust accumulation assumed the dust came entirely from meteor impacts and falling cosmic dust. “But that’s not enough to account for what we measured,” O’Brien said.
With no atmosphere for wind, the Moon’s soil should be stagnant. However, O’Brien said a popular idea of a “dust atmosphere” on the Moon could explain the difference. During each lunar day, solar radiation is strong enough to knock a few electrons out of atoms in dust particles, building up a slight positive charge. On the night time side of the Moon, electrons from the flow of energetic particles, called the solar wind, which are blasted out from the Sun, strike dust particles and give them a small negative charge. Where the illuminated and dark regions of the moon meet, electric forces could levitate this charged dust, potentially lofting grains high into the lunar sky.
The idea of levitating lunar dust could soon be confirmed by NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE), launched in September. LADEE now orbits the moon about every two hours at an altitude of eight to 37 miles (12-60 kilometers) above the moon's surface.
For about 100 days, the spacecraft will gather detailed information about the structure and composition of the thin lunar atmosphere and determine whether dust is being lofted into the lunar sky. "A thorough understanding of the characteristics of our lunar neighbour will help researchers understand other small bodies in the solar system, such as asteroids, Mercury, and the moons of outer planets," said Sarah Noble, LADEE program scientist at NASA Headquarters in Washington.