The research is being led by Michael Collier at NASA's Goddard Space Flight Center, Greenbelt, Md., as part of the Dynamic Response of the Environment At the Moon (DREAM) team in partnership with the NASA Lunar Science Institute (NLSI), managed at NASA's Ames Research Center, Moffett Field, Calif.
This is a view from NASA's Lunar Reconnaissance Orbiter spacecraft across the north rim of Cabeus crater. The leaping dust behavior may be observed on the moon in places like this where sunlit areas are close to shaded regions. Credit: NASA/GSFC/Arizona State University
"The motion of an individual dust particle is like a pendulum or a swing," says Collier. "We predict dust can swarm like bees around a hive over partially shaded regions on the moon and other airless objects in the solar system, such as asteroids. We found that this is a new class of dust motion. It does not escape to space or bounce long distances as predicted by others, but instead stays locally trapped, executing oscillations over a shaded region of 1 to 10 meters (yards) in size. These other trajectories are possible, but we now show a third new motion that is possible." Collier is lead author of a paper on this research published October 2012 in Advances in Space Research.
This effect should be especially prominent during dusk and dawn, according to the team, as regions become partially illuminated while features like mountains and crater rims cast long shadows.
"The dust is an indicator of unusual surface electric fields," says William Farrell of NASA Goddard, a co-author on the paper and lead of the NLSI DREAM team. "In these shaded regions, the surface is negatively charged compared to the sunlit regions. This creates a locally complex, larger electric field with separate positively and negatively charged regions, called a dipole field, over the shaded region. The dust performed its swinging motion under the influence of this dipole. Such a surface process occurring on the moon at the line where night transitions to day, called the terminator, might also occur at small bodies like asteroids. It might be a fundamental process occurring at airless rocky bodies."
There is evidence that dust actually moves this way over the lunar surface. "There are hints for this type of dust swarm in Surveyor images. A twilight was observed over the landed platforms during dusk and dawn. This was surprising at first because the moon does not have a dense enough atmosphere to scatter light when the sun is below the horizon. It was long considered to be light scattered from lifted dust. This model suggests the dust is really leaping or swarming overtop a large number of shaded regions that would exist along the lunar dusk/dawn line, called the lunar terminator. It's a natural fit. Charged lunar dust transport is also believed responsible for the Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment’s observation of highly charged dust near the terminator," adds Collier.
To our eyes, the moon has no apparent activity and seems dead. However, because it has almost no atmosphere, the moon is exposed to the solar wind, a thin stream of electrically conducting gas called plasma blown off the surface of the sun at around a million miles per hour. The effects of sunlight and the solar wind generate a bustle of unseen commotion at the moon. On the day-lit side, sunlight knocks negatively charged electrons off the surface, giving it a positive charge. On the night side or in shadow, electrons from the solar wind rush in, giving the surface a negative charge.
The exact mechanism for launching lunar dust is not uniquely known. Micro-meteoroid impacts can transfer energy to the surface to launch particulates. Also, a rough surface has small, localized concentrations of electric fields that could lift dust electrostatically from the surface. The pendulum motion then happens because sunlit areas on the moon tend to get positively charged, while shaded areas become negatively charged. Since like charges repel each other, a positively charged dust grain in a sunlit area gets pushed away from the positively charged surface. If there were no negatively charged area nearby, the dust grain would rise straight up. However, since opposite charges attract, the positively charged dust gets pulled toward the negatively charged crater floor, bending its path over the crater. Dust launched from the sunlit area with just the right speed will pass over the shaded floor of the crater to the sunlit area on the other side, where the positively charged surface there will reflect it back over the crater again. When many particles do this, the model predicts there should be a swarm or canopy of dust over the crater.
If there were no complications, the particle could continue to bounce between sunlit areas on opposite sides of the crater indefinitely. However, in reality, things like differences in crater rim height, roughness on the crater floor, and interference from the solar wind that weakens the electric field produced by the surface charges can alter the particle's path. These perturbations cause the dust to eventually either fall into the crater or be launched away. "This model provides a natural explanation for the observation of dust ponds inside craters on the asteroid Eros," says Collier.
"Calculating how these complications will affect the path of a dust particle on the moon and around asteroids are good areas for future research," says Collier. "Additionally, we're not sure how many particles get charged and move like this – is it something like one in a thousand, one in a million, or one in a billion? We'd like to do more studies to see how likely it is that a particle will behave this way. Since most of the lunar surface is covered in dust, even one in a billion would still be significant." The team is also planning on examining Apollo-era images to evaluate possible evidence for dust canopies over shadowed craters.
The team includes Collier, Farrell, and Timothy Stubbs, also at NASA Goddard. The research was funded by the NLSI.
For more information about the DREAM team visit:
NLSI is a virtual organization funded by NASA's Science Mission Directorate and the Human Exploration Office in Washington, which enables collaborative, interdisciplinary research in support of NASA lunar science programs. The institute uses technology to bring scientists together from around the world and is comprised of competitively selected U.S. teams and several international partners.
For more information about the NLSI, visit:
http://lunarscience.nasa.govNancy Neal-Jones / Bill Steigerwald
Bill Steigerwald | EurekAlert!
Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences