Lunar Dust Problem Re-opened
Long-lost Apollo data on lunar dust accumulation has been found, showing a tenfold increase over previous estimates. What does that imply about the age of the moon?
PhysOrg reported that 46-year-old data from Apollo experiments on the moon have been rediscovered, allowing lunar scientists to calculate the rate of dust accumulation (Headline: “Rediscovered Apollo data gives first measure of how fast moon dust piles up.”). A new paper in Space Weather, a publication of the American Geophysical Union (AGU), updates previous estimates based on measurements from detectors at the Apollo 12, 14, and 15 landing sites. Dust accumulation is an order of magnitude greater than previously thought, although it could be significantly less, the abstract says. PhysOrg did not indicate any doubt about it:
Now, more than 40 years later, scientists have used the rediscovered data to make the first determination of how fast lunar dust accumulates. It builds up unbelievably slowly by the standards of any Earth-bound housekeeper, their calculations show – just fast enough to form a layer about a millimeter (0.04 inches) thick every 1,000 years. Yet, that rate is 10 times previous estimates.
The “faster-than-expected pileup” of dust explains why detectors lost sensitivity over the years. Brian O’Brien, who designed the detectors in 1966, finally recovered the data for a fresh look from his own backups when he heard in 2006 that NASA had lost their copies. Now aged 79, he co-authored the new paper with Monique Hollick who had not even been born then. PhysOrg used an analogy to explain the results:
In his experiment, dust collected on small solar cells attached to a matchbox-sized case over the course of six years, throughout three Apollo missions. As the granules blocked light from coming in, the voltage the solar cells produced dropped. The electrical measurements indicated that each year 100 micrograms of lunar dust collected per square centimeter. At that rate, a basketball court on the Moon would collect roughly 450 grams (1 pound) of lunar dust annually.
The detectors had been hardened against solar radiation, but not against dust accumulation. The decline in sensitivity of the detectors provides a measure of dust accumulation. If 0.04 inches per 1,000 years can be taken as an average, some 15,000 feet of dust should have accumulated over the assumed age of 4.5 billion years. Even if starting the dust clock after the assumed Late Heavy Bombardment, the dust should be nearly 12,000 feet thick (over 2 miles) unless other processes can provide sinks against accumulation.
O’Brien said that the new rate is more than can be accounted for from meteors and cosmic dust. He believes the difference might be explained by levitation of dust from the sunlit side, when the solar wind imparts charge to dust particles, lofting them above the surface where they can migrate. The LADEE spacecraft launched in September might be able to account for the volume of dust in the thin lunar atmosphere.
Before and after Apollo, some creationists used lunar dust accumulation estimates to argue for a young moon. Those of us who lived through the days of Apollo remember Neil Armstrong and Buzz Aldrin surprised at being able to scrape through a thin layer of dust to bare rock. Notable scientists like Isaac Asimov and Thomas Gold had expected deep layers of dust. Before Apollo 11, the unmanned Surveyors showed in 1966, however, that thick dust was not there. It seemed obvious that the expectations of the long-agers had been falsified when those astronaut boots found only a thin layer. Most creationists abandoned the argument when later estimates significantly lowered the accumulation rate. CMI has advised creationists not to use this argument (details: CMI). Now, however, this new data looks interesting. Is it time to re-open that investigation? (One creation scientist who has kept the argument alive is Dr. Walt Brown, who performed his own calculations.)
For a robust analysis, investigators would need to consider all sources and sinks, and determine any non-linear or localized processes. For instance, if levitation merely moves dust from the sunlit side to the dark side and back again, accumulation may not result. Does levitation lead to escape? The accumulation at the 3 landing sites might reflect local accumulation, not global averages. New investigations would need to consider all reasonable dust sources from asteroids, cosmic dust and other non-lunar material. Our quick calculation, though, shows at least two miles of dust should have accumulated in 3.8 or 4.5 billion years, based on what the new paper says. It’s not there. Where did it go?
Three aspects of the PhysOrg story might motivate reclaiming the lunar dust argument for an upper limit on the moon’s age. (1) One is that the new estimate is 10 times higher than previously thought. (2) Another is the steady decline in sensitivity of the instruments; it indicates dust is accumulating at a steady, predictable rate, at least at the three Apollo sites, rather than reaching a steady state. (3) A final aspect is how silent the article was about the implications of lunar age. Are the secularists afraid to address that question? It resembles their reaction to Titan: when the ethane accumulation was far below the global ocean they predicted, they changed the subject. That silence is telling. We’ll leave it to other interested investigators to look into this matter in more detail.