It is now accepted that dust is the number-one environmental problem on the moon and interest has grown since 2004, when President Bush announced plans for human missions to the moon by 2020.
The adhesive strength of dust on the Moon, the ubiquitous ‘sticky’ dust that tormented the Apollo astronauts, changes as the intensity of sunlight alters when solar elevation angle changes.
Dust pulled by lunar gravity fell off a vertical surface by mid-morning as the rising sun shone on it at a more glancing angle. All the dust was gone after the first lunar night.
This finding, greeted by one lunar dust scientist as “remarkable”, was one of a suite of discoveries reported 40 years after Apollo, in May 2009 in Geophysical Research Letters.
The measurements were made by the matchbox-sized Dust Detector Experiments (DDEs) I invented before dinner on National Airlines Flight 58, Los Angeles to Houston, on 12 January 1966. A DDE was put on the moon by Apollo 11, 12, 14 and 15 astronauts, and its measurements every 54 seconds transmitted to Earth.
The DDE was a hitch-hiking, delightfully minimalist experiment.
Three solar cells give output voltages predictable from the reliable light source, the sun. Output decreases by 10 per cent if about 0.5 milligrams per square centimetre mg of lunar dust obscures a surface. The temperature of each cell is also measured. The six measurements provide absorptivity and emissivity values that dictate thermal controls as lunar temperature varies from minus 1700C to 1200C.
Lunar dust thrown up by rocket exhausts of the Apollo 11 Lunar Module contaminated the shiny gold surface of a 47-kilogram seismometer deployed 17 metres away.
The only other active experiment deployed on that historic expedition, a tiny (0.27kg) DDE measured2 – and I eventually succeeded in having published3 – the contamination. The seismometer overheated by 500F and was terminated after 21 days instead of the nominal two years.
In 2006 the NASA website on Apollo 11 Dust Detector stated and states in June 2009, “The original tapes were subsequently misplaced before they could be archived, the only existing data from these experiments are on the plots.”
So I advised NASA that I had safely, in Perth, my original principal investigator records, including 100 paper charts, calibrations etc. and 173 digital tapes, with six million measurements. Professor John de Laeter AO FTSE and Laboratory Manager Glen Lawson, of the Department of Applied Physics at Curtin University, had kindly saved the computer 10-inch tapes for me. They are now stored with SpectrumData.
I revisited my personal files, leading to the “highlighted” May 2009 paper, my first publication on lunar dust since 1970.
Now two other papers are in preparation, and NASA asked me to give two talks to the 2nd Lunar Science Forum in California in July 2009. Steps are under way to read once more the outdated seven-track computer tapes in Perth.
Over 40 years there has been a massive change in cultural attitudes to lunar dust.
Before Apollo, science fiction writer Isaac Asimov popularised a view that spacecraft landing on the moon would sink majestically out of sight in deep lunar dust. The lunar surface, unprotected by an atmosphere such as Earth’s, has been pulverised for 4000 million years by 25,000-kilometre-per-hour meteors, rocks large and small.
In 1966, soft-landing Russian Luna and USA Surveyor missions showed such fears to be indeed science fiction.
Once Apollo engineers were free of that great risk, they largely treated dust as a housekeeping problem for astronauts to manage personally, with brushes and a vacuum system. Yet astronauts on Apollo 17, the last mission, were very dusty indeed. Image
It is now accepted that dust is the number-one environmental problem on the moon.
The zero-risk culture of Apollo engineering dominated lunar research of the time, necessarily so because astronaut safety had to dominate scientific research.
The urgency of trial-and-error mitigation of hazardous effects of dust movements gave no time or resources for science to discover their causes.
Interest in lunar dust has grown since 2004 when President Bush announced plans for human missions to the moon by 2020. While hypotheses and computer modelling of lunar dust are now better funded, for the next few years the only hard data ‘ground truth’ about surface dust will continue to be mainly from DDEs and hard-learned anecdotal lessons from Apollo.
Apollo 12 astronauts landed blind because of clouds of dust below 40 feet altitude stirred up by rocket exhausts. On the surface, dust was readily kicked up by astronauts. It clung to anything and everything, from Apollo hardware, optics and deployed experiments to spacesuits.
Lunar dust has an average particle size of about 70 microns, about the thickness of a human hair. But many particles can be only a few microns, and grains tend be sharp and angular. Inhaled they would be a health hazard. They affected chronometers.
With Apollo 12, Alan Bean deployed the scientific package 130 metres from the lunar module. The photo here shows the DDE and what I have called “collateral” lunar dust splashed on Apollo hardware from Alan’s spacesuit.
As the Apollo 12 astronauts left the moon, rocket exhausts then cleansed horizontal and vertical solar cells of DDE differently, providing hitherto-lacking insight into the stickyness of lunar dust.
Dust adhesion encountered by overnighting future astronauts in the middle of lunar days may be much greater than with Apollo astronauts who walked there only in early lunar mornings.
A new field of science has grown from the moon being recognised as a unique and fascinating, ever-changing laboratory of “dusty plasmas”.
With an atmosphere and magnetic fields only 10-15 and about 10-3 the strength of those that shield the Earth, during each 350-hour day the moon is bombarded by the solar wind, the hot atmosphere of the sun, with proton densities about 10 per cc travelling at 300km/sec.
By day the moon is also bathed in a dense sea of photoelectrons, knocked out of dust particles by energetic ultraviolet and X-rays in raw sunlight, leaving dust a few volts positive.
At night, the long magnetospheric tail of the Earth, fluttering comet-like in the solar wind, brings other plasmas to the moon, richer in the more energetic electrons and protons that cause the divine writing of auroras in polar regions back on Earth. Cosmic and solar nuclei with even greater energies have unlimited access.
At sunrise and sunset, electrically charged dust may levitate.
We now know a few of the ways that lunar dust is richly mysterious. But as yet we have few facts.
So scientific justifications for exploration of the moon in the 21st century are increasingly energised by dusty-plasma physicists, just as they were in the 20th century by geologists asking Apollo astronauts to bring back special rocks.
Truly we live in interesting times.
Dr Brian J O’Brien is an environmental and strategic consultant, principal of Brian J O’Brien and Associate and Adjunct Professor of Physics, University of Western Australia. He is a former Director and Chair of the Environmental Protection Authority of WA. He took his PhD at the University of Sydney and then worked in the US for 10 years – at the University of Iowa and then as Professor of Space Science at Rice University, Houston, from 1963–68.
Editor's Note: An opinion provided by the Australian Academy of Technological Sciences and Engineering.