Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

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

09.12.2014

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, robert.burnham@asu.edu

(480) 458-8207

Mars Space Flight Facility

Robert Burnham | EurekAlert!
Further information:
https://asunews.asu.edu/20141208-titan-winds

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

More articles from Physics and Astronomy:

nachricht Scientists propose synestia, a new type of planetary object
23.05.2017 | University of California - Davis

nachricht Turmoil in sluggish electrons’ existence
23.05.2017 | Max-Planck-Institut für Quantenoptik

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: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

Im Focus: Using graphene to create quantum bits

In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.

In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...

Im Focus: Bacteria harness the lotus effect to protect themselves

Biofilms: Researchers find the causes of water-repelling properties

Dental plaque and the viscous brown slime in drainpipes are two familiar examples of bacterial biofilms. Removing such bacterial depositions from surfaces is...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

Innovation 4.0: Shaping a humane fourth industrial revolution

17.05.2017 | Event News

 
Latest News

Scientists propose synestia, a new type of planetary object

23.05.2017 | Physics and Astronomy

Zap! Graphene is bad news for bacteria

23.05.2017 | Life Sciences

Medical gamma-ray camera is now palm-sized

23.05.2017 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>