Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Dunes on Titan need firm winds to move, experiments at ASU show


Saturn's largest moon, Titan, is one of the few solar system bodies – and the only planetary moon – known to have fields of wind-blown dunes on its surface. (The others are Venus, Earth and Mars.)

New research, using experimental results from the high-pressure wind tunnel at Arizona State University's Planetary Aeolian Laboratory, has found that previous estimates of how fast winds need to blow to move sand-size particles around on Titan are about 40 percent too low.

Lines of dunes crawl across the surface of Titan, Saturn's largest moon, in a radar image showing dunes as dark. Experiments at ASU's wind tunnel indicate the dune particles move only under winds that blow stronger than scientists previously thought.

Photo by: NASA/JPL-Caltech/ASI

A team of scientists led by Devon Burr of the University of Tennessee, Knoxville reported the findings Dec. 8 in a paper published in the journal Nature. James K. Smith, engineer and manager of ASU's Planetary Aeolian Laboratory, is one of the paper's co-authors.

Saturn and Titan orbit about ten times farther from the sun than Earth. Scientists got their first detailed information about Titan when the Cassini/Huygens orbiter and lander arrived in 2004. The short-lived Huygens lander took photos when it reached the surface and as it was descending through Titan's dense, smoggy atmosphere, which has 1.4 times greater pressure than Earth's. These images, plus studies using instruments on the Cassini orbiter, revealed that Titan's geological features include mountains, craters, river channels, lakes of ethane, methane and propane – and dunes.

Dunes begin to form when the wind picks up loose particles from the ground and drives them to hop, or saltate, downwind. A key part of understanding dunes is to identify the threshold wind speed that causes dune particles to start to move. Geologists have found threshold speeds for sand and dust under various conditions on Earth, Mars and Venus. But for Titan, with its bizarre conditions, this remained unknown.

Particles of 'sand' as light as freeze-dried coffee

On Titan, where the surface temperature is negative 290 degrees Fahrenheit, even "sand" is probably unlike sand on Earth, Mars or Venus. From the Cassini observations and other data, scientists think it is composed of small particles of solid hydrocarbons (or ice wrapped in hydrocarbons), with a density about one-third that of terrestrial sand. In addition, Titan's gravity is low, roughly one-seventh that on Earth. Combined with the particles' low density, this gives them a weight of only about four percent that of terrestrial sand, or roughly as light as freeze-dried coffee grains.

The scientists led by Burr began their study with carefully designed wind tunnel experiments. "We refurbished the high-pressure wind tunnel previously used to study conditions on Venus," Smith explains. To recreate in the tunnel on Earth the wind conditions on Titan, the scientists had to increase the air pressure in the wind tunnel to about 12 times the surface pressure of Earth. And they compensated for the low density of Titan "sand" and the moon's reduced gravity through numerical modeling.

In the end, the Burr team explains, "This simulation reproduces the fundamental physics governing particle motion thresholds on Titan." They add that previous studies, which had extrapolated from wind tunnel experiments designed to mimic conditions on Earth and Mars, produced results that were questionable under Titan's conditions.

The outcome of the wind tunnel experiments show that the previous calculations for wind speeds necessary to lift particles were about 40 to 50 percent too slow. The new experiments show that near the surface of Titan, the most easily moved sand-size particles need winds of at least 3.2 miles per hour (1.4 meters per second) to start moving.

That doesn't sound like much, says Nathan Bridges of the Johns Hopkins University Applied Physics Laboratory, one of the co-authors, "but it makes more sense when you realize this is a dense atmosphere blowing against particles that are very light."

A higher threshold wind speed for making particles move creates an either/or situation in which weak, everyday winds do little or nothing to surface particles, but occasional strong ones readily blow them around and reshape the dunes. The pattern of dunes on Titan shows that despite prevailing winds blowing from the east, the dunes appear shaped by winds from the west, which occur more rarely. Thus, the new work indicates that Titan's dunes are seldom stirred into motion – only whenever conditions produce strong westerly winds.

For simplicity, the wind-tunnel modeling ignored some factors, among them whether Titan dune particles are sticky. If they are, the paper's scientists note, then it will take yet-stronger winds to get the particles moving, and the contrasts will be even greater between the normal east wind pattern and the stronger west winds that shape the dunes.

Bridges says, "Titan is a strange place indeed."

The facility that has grown to become ASU's Planetary Aeolian Laboratory was founded in the mid-1970s by the late Ronald Greeley of ASU. The laboratory, located at NASA's Ames Research Center in Mountain View, California, has been used for many studies of how wind interacts with particles of sand, dust and rock. Scientists have also used it to investigate what blowing sand and dust do to Mars spacecraft, such as NASA's Opportunity and Curiosity rovers. ASU operates the laboratory through an agreement with NASA.

The School of Earth and Space Exploration is an academic unit of ASU's College of Liberal Arts and Sciences.

Robert Burnham,

(480) 458-8207

Mars Space Flight Facility

Robert Burnham | EurekAlert!
Further information:

Further reports about: Arizona Dunes Mars Planetary Space Titan conditions threshold wind speed wind tunnel winds

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>