Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Titan Gets a Dune "Makeover"

18.01.2013
Titan's siblings must be jealous. While most of Saturn's moons display their ancient faces pockmarked by thousands of craters, Titan – Saturn's largest moon – may look much younger than it really is because its craters are getting erased. Dunes of exotic, hydrocarbon sand are slowly but steadily filling in its craters, according to new research using observations from NASA's Cassini spacecraft.

"Most of the Saturnian satellites – Titan's siblings – have thousands and thousands of craters on their surface. So far on Titan, of the 50 percent of the surface that we've seen in high resolution, we've only found about 60 craters," said Catherine Neish, a Cassini radar team associate based at NASA's Goddard Space Flight Center, Greenbelt, Md.


This image taken with the Cassini radar instrument shows two craters on Titan: the crater Sinlap (left), which is a relatively 'fresh' crater, with a depth-to-diameter ratio close to what we see on Ganymede, and Soi (right), an extremely degraded crater, with a very small depth compared to similar craters on Ganymede. These craters are both about 80 km (almost 50 miles) in diameter. The Sinlap image was taken on Feb. 15, 2005. The Soi image is a mosaic of two images from May 21, 2009 and July 22, 2006. Credit: Catherine Neish/NASA/JPL-Caltech/ASI/GSFC

"It's possible that there are many more craters on Titan, but they are not visible from space because they are so eroded. We typically estimate the age of a planet's surface by counting the number of craters on it (more craters means an older surface). But if processes like stream erosion or drifting sand dunes are filling them in, it's possible that the surface is much older that it appears."

"This research is the first quantitative estimate of how much the weather on Titan has modified its surface," adds Neish.

Titan is the only moon in the solar system with a thick atmosphere, and the only world besides Earth known to have lakes and seas on its surface. However, with a frigid surface temperature of around minus 290 degrees Fahrenheit (94 kelvins), the rain that falls from Titan's skies is not water but instead liquid methane and ethane, compounds that are normally gases on Earth.

Neish and her team made the discovery by comparing craters on Titan to craters on Jupiter's moon Ganymede. Ganymede is a giant moon with a water ice crust, similar to Titan, so craters on the two moons should have similar shapes. However, Ganymede has almost no atmosphere and thus no wind or rain to erode its surface.

"We found that craters on Titan were on average hundreds of yards (meters) shallower than similarly sized craters on Ganymede, suggesting that some process on Titan is filling its craters," says Neish, who is lead author of a paper about this research published online in the journal Icarus Dec. 3, 2012.

The team used the average depth-versus-diameter trend for craters on Ganymede derived from stereo images from NASA's Galileo spacecraft. The same trend for craters on Titan was calculated using estimates of the crater depth from data derived from images made by Cassini's radar instrument.

Titan's atmosphere is mostly nitrogen with a trace of methane and other, more complex molecules made of hydrogen and carbon (hydrocarbons). The source of Titan's methane remains a mystery because methane in the atmosphere is broken down over relatively short timescales by sunlight. Fragments of methane molecules then recombine into more complex hydrocarbons in the upper atmosphere, forming a thick, orange smog that hides the surface from view. Some of the larger particles eventually rain out on to the surface, where they appear to get bound together to form the sand.

"Since the sand appears to be produced from the atmospheric methane, Titan must have had methane in its atmosphere for at least several hundred million years in order to fill craters to the levels we are seeing," says Neish. However, researchers estimate Titan's current supply of methane should be broken down by sunlight within tens of millions of years, so Titan either had a lot more methane in the past, or it is being replenished somehow.

Team members say it's possible that other processes could be filling the craters on Titan: erosion from the flow of liquid methane and ethane for example. However, this type of weathering tends to fill a crater quickly at first, then more slowly as the crater rim gets worn down and less steep. If liquid erosion were primarily responsible for the infill, then the team would expect to see a lot of partially filled craters on Titan. "However, this is not the case," says Neish. "Instead we see craters at all stages; some just beginning to be filled in, some halfway, and some that are almost completely full. This suggests a process like windblown sand, which fills craters and other features at a steady rate."

All solid materials under stress flow very slowly over time. This is called viscous flow, and it is like what happens when someone takes a scoop out of a fresh tub of whipped cream -- the material slowly flows in to fill the hole and flatten the surface. Craters on icy satellites tend to get shallower over time as the ice flows viscously, so it's possible that some of the shallow craters on Titan are simply much older or experienced a higher heat flow than the similarly sized, fresh craters on Ganymede studied in this work.

However, Titan's crust is mostly water ice, and at the extremely low temperatures on Titan, ice shouldn't flow enough to account for such a large difference in depth compared to the Ganymede craters, according to the team. Also, just like stream erosion, deformation from viscous flow tends to happen rapidly at first, then more slowly as the material adjusts, so one would expect to see a lot of partially filled craters on Titan if its surface was deforming easily through viscous flow.

As Cassini flies past Titan on its multi-year tour of Saturn and its moons, the radar instrument gradually builds up a map of the surface. To date, the instrument has provided data in strips covering approximately 50 percent of Titan's surface. The craters measured by the team are all within about 30 degrees of the equator, a relatively dry region on Titan.

"However, the presence of liquids on the surface and in the near subsurface can also cause extensive modification to crater shape, as is observed on Earth," says Neish. "In the case of Titan, liquids consist of hydrocarbons, either as wet sediments (such as those observed at the Huygens landing site) or shallow marine environments (such as the lakes observed at the north and south poles). Craters formed in similar environments on Earth lack any significant surface topography, including the absence of a raised rim, as wet sediments slump into the crater. It is possible that the lack of topography associated with marine-target impacts may help to explain the relative scarcity of impact craters observed near the poles of Titan. If Titan's polar regions are saturated by liquid hydrocarbons, craters formed in those regions may lack any recognizable topographic expression."

The team thinks these considerations are good areas for more research, but based on the data so far, the difference in depth between craters on Titan and Ganymede is best explained by filling from windblown sand, although erosion from liquids and viscous flow might contribute to the modification of Titan's craters.

NASA's Cassini mission, managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and the NASA Postdoctoral Program, administered by Oak Ridge Associated Universities, funded the research.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries.

Nancy Neal-Jones / Bill Steigerwald
NASA's Goddard Space Flight Center, Greenbelt, Md.
Nancy.N.Jones@nasa.gov / William.A.Steigerwald@nasa.gov
Jia-Rui Cook
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Bill Steigerwald | EurekAlert!
Further information:
http://www.nasa.gov
http://www.nasa.gov/mission_pages/cassini/whycassini/titan-makeover.html

More articles from Physics and Astronomy:

nachricht Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie

nachricht Seeing the quantum future... literally
16.01.2017 | University of Sydney

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: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>