December 31, 1969 |

Experiments led by researchers at the Georgia Institute of Technology suggest the particles that cover the surface of Saturn’s largest moon, Titan, are “electrically charged.” When the wind blows hard enough (approximately 15 mph), Titan’s non-silicate granules get kicked up and start to hop in a motion referred to as saltation. As they collide, they become frictionally charged, like a balloon rubbing against your hair, and clump together in a way not observed for sand dune grains on Earth — they become resistant to further motion. They maintain that charge for days or months at a time and attach to other hydrocarbon substances, much like packing peanuts used in shipping boxes here on Earth.

The findings have just been published in the journal Nature Geoscience.

“If you grabbed piles of grains and built a sand castle on Titan, it would perhaps stay together for weeks due to their electrostatic properties,” said Josef Dufek, the Georgia Tech professor who co-led the study. “Any spacecraft that lands in regions of granular material on Titan is going to have a tough time staying clean. Think of putting a cat in a box of packing peanuts.”

The electrification findings may help explain an odd phenomenon. Prevailing winds on Titan blow from east to west across the moon’s surface, but sandy dunes nearly 300 feet tall seem to form in the opposite direction.

“These electrostatic forces increase frictional thresholds,” said Josh Méndez Harper, a Georgia Tech geophysics and electrical engineering doctoral student who is the paper’s lead author. “This makes the grains so sticky and cohesive that only heavy winds can move them. The prevailing winds aren’t strong enough to shape the dunes.”

To test particle flow under Titan-like conditions, the researchers built a small experiment in a modified pressure vessel in their Georgia Tech lab. They inserted grains of naphthalene and biphenyl — two toxic, carbon and hydrogen bearing compounds believed to exist on Titan’s surface — into a small cylinder. Then they rotated the tube for 20 minutes in a dry, pure nitrogen environment (Titan’s atmosphere is composed of 98 percent nitrogen). Afterwards, they measured the electric properties of each grain as it tumbled out of the tube.

“All of the particles charged well, and about 2 to 5 percent didn’t come out of the tumbler,” said Méndez Harper. “They clung to the inside and stuck together. When we did the same experiment with sand and volcanic ash using Earth-like conditions, all of it came out. Nothing stuck.”

Earth sand does pick up electrical charge when it’s moved, but the charges are smaller and dissipate quickly. That’s one reason why you need water to keep sand together when building a sand castle. Not so with Titan.

“These non-silicate, granular materials can hold their electrostatic charges for days, weeks or months at a time under low-gravity conditions,” said George McDonald, a graduate student in the School of Earth and Atmospheric Sciences who also co-authored the paper.

Visually, Titan is the object in the solar system most like Earth. Data gathered from multiple flybys by Cassini since 2005 have revealed large liquid lakes at the poles, as well as mountains, rivers and potentially volcanoes. However, instead of water-filled oceans and seas, they’re composed of methane and ethane and are replenished by precipitation from hydrocarbon-filled clouds. Titan’s surface pressure is a bit higher than our planet — standing on the moon would feel similar to standing 15 feet underwater here on Earth.

“Titan’s extreme physical environment requires scientists to think differently about what we’ve learned of Earth’s granular dynamics,” said Dufek. “Landforms are influenced by forces that aren’t intuitive to us because those forces aren’t so important on Earth. Titan is a strange, electrostatically sticky world.”

Researchers from the Jet Propulsion Lab, University of Tennessee-Knoxville and Cornell University also co-authored the paper, which is titled “Electrification of Sand on Titan and its Influence on Sediment Transport.”

The study is partially supported by the National Science Foundation (EAR-1150794). Méndez Harper held a National Science Foundation graduate fellowship while conducting the study. McDonald has a National Defense Science and Engineering Graduate Fellowship. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors.

December 31, 1969 |

Negotiating uneven ground can be challenging for people who use lower-limb prostheses to walk, so researchers spend time searching for solutions that will allow greater stability in these situations. Manufacturers of prosthetic feet have contributed to a solution by adding multiaxial features that better reproduce the behavior of human ankles, which can stiffen as the terrain warrants. However, School of Biological Sciences Senior Lecturer W. Lee Childers found that there was a lack of evidence evaluating the prosthetic ankle stiffness as it relates to the user’s dynamic balance and gait over uneven terrain. Thus, his continuing research focuses on defining the effect of multiaxial stiffness on gait stability among people with unilateral transtibial amputations....“The main focus of this work was to justify that it is a good thing for prosthetic feet to have multiaxial function,” Childers says, because if it can prevent falls among its users, its value is demonstrated to the payers.

December 31, 1969 |

You never know when a frog playing an electronic game will lead to an experiment on the physics of saliva....Alexis C. Noel, a Ph.D. student in mechanical engineering at Georgia Tech, and her supervisor, David L. Hu, were watching a viral YouTube video in which a frog is attacking the screen of a smartphone running an ant-smashing game. It appears to be winning. They started wondering how — in reality — frog tongues stick to insects so quickly when they shoot out to grab them, and decided it was a phenomenon worth studying. David Hu is an associate professor of mechanical engineering and of biology, as well as an adjunct associate professor of physics, at Georgia Tech. 

POSTDOCTORAL POSITION in the molecular biology of chemoreception

A POSTDOCTORAL POSITION in the molecular biology of chemoreception is available in the laboratory of Dr. Nael McCarty at Emory University (http://www.pedsresearch.org/people/faculty/nael-a-mccarty).  This project is funded by the National Science Foundation in collaboration with Prof. Julia Kubanek (http://www.biosci.gatech.edu/people/julia-kubanek) at the Georgia Institute of Technology.

NEUROSCIENCE TEACHING FACULTY POSITIONS

The COLLEGE OF SCIENCES of the GEORGIA INSTITUTE OF TECHNOLOGY invites applications for a 12-month, permanent, non-tenure track faculty position (Academic Professional) to contribute to the development of a new B.S. degree program in neuroscience. The position will require classroom teaching as well as coordination of the associated laboratory, and undergraduate advisement.

Pluto’s relationship with its moon Charon is one of the more unusual interactions in the solar system due to Charon’s size and proximity. It’s more than half of Pluto’s diameter and orbits only 12,000 or so miles away. To put that into perspective, picture our moon three times closer to Earth, and as large as Mars.

A new study from the Georgia Institute of Technology provides additional insight into this relationship and how it affects the continuous stripping of Pluto’s atmosphere by solar wind. When Charon is positioned between the sun and Pluto, the research indicates that the moon can significantly reduce atmospheric loss.

“Charon doesn’t always have its own atmosphere,” said Carol Paty, a Georgia Tech associate professor in the School of Earth and Atmospheric Sciences. “But when it does, it creates a shield for Pluto and redirects much of the solar wind around and away.”

This barrier creates a more acute angle of Pluto’s bow shock, slowing down the deterioration of the atmosphere. When Charon doesn’t have an atmosphere, or when it’s behind or next to Pluto (a term scientists call “downstream”), then Charon has only a minor effect on the interaction of the solar wind with Pluto.

The study’s predictions, performed before the New Horizons probe collected and returned data to Earth, is consistent with the measurements made by the spacecraft about Pluto’s atmospheric loss rate. Previous estimates at the time of the study were at least 100 times higher than the actual rate.

The research is currently published in a special Pluto issue of the journal Icarus.

John Hale is the Georgia Tech student who co-led the study with Paty. He says the Pluto system is a window into our origins because Pluto hasn’t been subjected to the same extreme temperatures as objects in closer orbits to the sun. 

“As a result, Pluto still has more of its volatile elements, which have long since been blown off the inner planets by solar wind,” Hale said. “Even at its great distance from the sun, Pluto is slowly losing its atmosphere. Knowing the rate at which Pluto’s atmosphere is being lost can tell us how much atmosphere it had to begin with, and therefore what it looked like originally. From there, we can get an idea of what the solar system was made of during its formation.”

Hale and Paty also say their study affirms a popular hypothesis of Charon. The areas of discoloration near its lunar poles are likely caused by magnetized particles that have been shorn from Pluto’s atmosphere. These particles have accumulated and settled on Charon over billions of years, particularly when it is downstream of Pluto.

The project is supported by NASA grant NNX11AM40G. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors.

Event Details

Date/Time:

December 31, 1969 |

Pluto’s relationship with its moon Charon is one of the more unusual interactions in the solar system due to Charon’s size and proximity. It’s more than half of Pluto’s diameter and orbits only 12,000 or so miles away. To put that into perspective, picture our moon three times closer to Earth, and as large as Mars.

A new study from the Georgia Institute of Technology provides additional insight into this relationship and how it affects the continuous stripping of Pluto’s atmosphere by solar wind. When Charon is positioned between the sun and Pluto, the research indicates that the moon can significantly reduce atmospheric loss.

“Charon doesn’t always have its own atmosphere,” said Carol Paty, a Georgia Tech associate professor in the School of Earth and Atmospheric Sciences. “But when it does, it creates a shield for Pluto and redirects much of the solar wind around and away.”

This barrier creates a more acute angle of Pluto’s bow shock, slowing down the deterioration of the atmosphere. When Charon doesn’t have an atmosphere, or when it’s behind or next to Pluto (a term scientists call “downstream”), then Charon has only a minor effect on the interaction of the solar wind with Pluto.

The study’s predictions, performed before the New Horizons probe collected and returned data to Earth, is consistent with the measurements made by the spacecraft about Pluto’s atmospheric loss rate. Previous estimates at the time of the study were at least 100 times higher than the actual rate.

The research is currently published in a special Pluto issue of the journal Icarus.

John Hale is the Georgia Tech student who co-led the study with Paty. He says the Pluto system is a window into our origins because Pluto hasn’t been subjected to the same extreme temperatures as objects in closer orbits to the sun. 

“As a result, Pluto still has more of its volatile elements, which have long since been blown off the inner planets by solar wind,” Hale said. “Even at its great distance from the sun, Pluto is slowly losing its atmosphere. Knowing the rate at which Pluto’s atmosphere is being lost can tell us how much atmosphere it had to begin with, and therefore what it looked like originally. From there, we can get an idea of what the solar system was made of during its formation.”

Hale and Paty also say their study affirms a popular hypothesis of Charon. The areas of discoloration near its lunar poles are likely caused by magnetized particles that have been shorn from Pluto’s atmosphere. These particles have accumulated and settled on Charon over billions of years, particularly when it is downstream of Pluto.

The project is supported by NASA grant NNX11AM40G. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors.

Laboratory Technician in Dr. Liang Han’s laboratory

A laboratory technician position is available in Dr. Liang Han’s laboratory in the School of Biological Sciences at Georgia Institute of Technology. Dr. Han’s group uses a combination of molecular genetic, immunohistochemical, fluorescence imaging and behavioral approaches to understand how the nervous system receives, transmits and interprets various stimuli to induce physiological and behavioral responses. We are interested in the basic mechanisms underlying somatosensation, including pain, itch and mechanical sensations.

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