Date: November 23, 2010
Title: Mysterious Moving Moon Dust
Podcaster: NASA Lunar Science Institute, with Dr. Mihaly Horanyi and Nancy Atkinson
Organization: NASA Lunar Science Institute
Description: Sometimes, when conditions are right, astronauts and spacecraft have seen mysterious, hazy dust clouds hovering well above the Moon’s surface. These Apollo-era observations of a dusty atmosphere about the Moon were complete unexpected, and scientists today are still trying to understand this phenomenon. To learn more about these mysterious moving dust particles, we talked with Dr. Mihaly Horanyi, from the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics, and he tells us about a new robotic mission that could help solve this mystery.
Bio: The NLSI brings together leading lunar scientists from around the world to further NASA lunar science and exploration.
Dr. Mihaly Horanyi is a professor is the Physics Department at the University of Colorado, Boulder. His research interests include theoretical and experimental investigations of space and laboratory dusty plasmas, electrodynamic processes and their role in the origin and evolution of the solar system, and the development of space instrumentation.
Prof. Horányi is the author of over 170 scientific papers. He is a Fellow of both the American Physical Society and the American Geophysical Union.
Nancy Atkinson is a science journalist and is the Senior Editor for Universe Today and project manager for 365 Days of Astronomy.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored anonymously and dedicated to the memory of Annie Cameron, at the time of NASA EPOXI flyby of Comet 103P/Hartley 0.0.155 AU above Tryphena, Great Barrier Island, New Zealand, located between Betelgeuse and Procyon on the edge of Canis Minor 4 November 2010.
Voice: You are listening to the NASA Lunar Science Institute podcast which highlights the latest news information of the Moon, on the Moon and from the Moon. It is produced from the NASA Lunar Science Institute at the Ames Research Center in Moffett Field, California.
Nancy Atkinson: Sometimes, when conditions are right, astronauts and spacecraft have seen mysterious, hazy dust clouds hovering well above the Moon’s surface. But how can this be? The Moon has no atmosphere, and without an atmosphere, how could dust be suspended above the Moon’s surface? Hi, this is Nancy Atkinson for the NASA Lunar Science Institute. Apollo-era observations of a dusty atmosphere about the Moon were complete unexpected, and scientists today are still trying to understand this phenomenon. To learn more about these mysterious moving dust particles, we talked with Dr. Mihaly Horanyi, from the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics, and he tells us about a new robotic mission that could help solve this mystery.
Dr. Mihaly Horanyi: The first indication that something strange is going on with the lunar surface goes back to the late 70’s with the Surveyor spacecraft that landed on the surface. They had TV cameras looking towards the western horizon, and when the Sun is set there is a brighter hovering cloud that appeared in the images that persisted for several hours. There are many other bits and pieces of observations of this kind. For example, the astronauts in the Apollo command module that stayed in orbit about the Moon, when they came to local sunrise they could make images of what they were hoping was the dark sky, but of course there is scattered light from the dust in interplanetary space. But the brightness also appeared to follow the lunar surface, again indicating that somehow dust is coming off the surface of the Moon. We had, in fact, a dust detector on the lunar surface, the Lunar Ejecta and Meteorite experiment on Apollo 17. It was supposed to measure the high speed impacts of micrometeorites hitting the moon. Instead the measurements showed an increase of fluxes that went up a hundred fold when day turned to night and night turned into day at that location.
Every single one of these measurements have an alternate explanation somehow. But it seems that the whole body of these observations is best explained by recognizing that dust — even on an airless body — can move around and come to life. Some can be due to other processes that we are used to. On Earth when we are discussing dust storms in the desert, that is obvious. There are big winds that pick up dust and transport it, even across continents. The Moon has no atmosphere of this kind, so other processes might surface that we overlook at the surface of the Earth because we have much more powerful things going on.
These processes are probably related to the plasma and radiation environment of the Moon, the electro-dynamic processes of the near surface lunar environment that can have strong enough electric fields and the surface can have enough electrostatic charges that can break the dust free and somehow shuffle it or move it around the surface.
These fields are certainly not random; there is some order and some transport that would come out of these. We could certainly try to do small experiments in the lab; set up similar situations that we expect happens on the Moon and indeed we find that dust is moving around on its own. The moon certainly is just one example in the solar system – there are countless other airless bodies like mercury or comets or asteroids far away from the sun where these processes might be at work. For example, the near-landing on the asteroid Eros, people noticed that the bottom of the craters are filled with fine dust, and there is not enough atmosphere, and certainly the body is too small have asteroid shakes – the asteroid version of earthquakes, so the possible transport that would trap or make dust pile up in some regions and move it from others, is most likely a plasma effect.
Nancy: What are some of the things that you and your colleagues are doing to try and learn more about this.
Horanyi: For the first set of experiments, imagine just a piece of surface with dust particles on it, and we shine light on this surface, so that half is illuminated, half is not, pretending that there is a terminator region, that the sun is set on one side and is still shining light on the other. When you shine light on the surface with properties that are appropriate, you can emit photo electrons, but you only emit electrons from the lit side, and some of those electrons land on the dark side, — you have a ppositive charge surplus on the lit and a negative charge pile-up on the night side. Across a couple of millimeters you can easily generate a potential difference of maybe a watt, or a handful of watts, which translates actually as a small-scale, but incredibly strong electric fields. This could be like a kilowatt over a meter. But of course, it only exists over a sharp boundary, and that sharp boundary may be the key to understanding how you get dust moving to begin with.
If I naively make an estimate of the charged density on the surface, it turns out that most of the grains have no charge at all – some will have one electron, normally. The electric fields that we calculate are certainly much bigger. But in this transient region where boundaries match up – lit and dark boundaries, or boundaries between where the surface is exposed to a plasma and where it is not – those sharp transitions could actually overcome adhesion between dust and the rest of the surface and start moving. And that’s where the story gets really interesting.
Nancy: There is a mission coming up, LADEE, can you explain that mission;
Horanyi: LADEE is a mission to explore the lunar dust and atmospheric environment. At a time it seemed urgent before a lot of humans go back and mess up the environment or change the environment quite a bit. Now it seems we have a bit more time. But certainly the mission is on track, so hopefully it will fly in early 2013 in low lunar orbit, as close to the surface as 30-50 km. It will carry three instruments, an infrared imager, a neutral mass spectrometer and a dust detector, which is built here at the Laboratory for Atmospheric and Space Physic at the University of Colorado. It is an impact dust detector that hopefully will be capable of measuring tiny, tiny, small particles that people argue are lofted from the surface. And that, in combination with UV imaging and the neutral mass spectrometer might put an end to this argument that we carry since the early 1970’s whether dust is really actively transported and shuffled around on the lunar surface or not.
For more information about the LADEE mission, see the show notes for this podcast, or go to www.nasa.gov/mission_pages/LADEE/
Thanks for listening, and we hope you’ll join again for more lunar missions and mysteries.
Voice: To find out more about this topic, visit our website at www.lunarscience.nasa.gov. Any opinions expressed are the individuals and do not necessarily reflect the opinion of NASA or the NASA Lunar Science Institute. This podcast is produced for educational purposes only. On behalf of the NASA Lunar Science Institute, thanks for listening.
End of podcast:
365 Days of Astronomy
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