by Charles Q. Choi, Space.com Contributor | April 13, 2015 03:27pm ET
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A methane ice cloud is seen over the north pole of
Saturn's moon Titan in this view captured by NASA's Cassini spacecraft
in December 2006. Scientists suspect that intense methane storms on
Titan may also sculpt towering dunes at the moon's equator. Credit: NASA/JPL/University of Arizona/LPGNantes |
When NASA's Cassini spacecraft began exploring Titan in2004, its most dramatic discovery was the field of dunes that covers nearly 15 percent of Titan's surface along its equator. These dark, massive dunes — the largest of their kind in the solar system — are made of exotic sand composed of hydrogen and carbon. They can be more than 330 feet (100 meters) high and are typically 18 to 31 miles (30 to 50 kilometers) long.
These long, colossal dunes pose one of Titan's greatest mysteries, as they seem to grow eastward, whereas models of Titan's atmosphere predict that surface winds at its equatorial latitudes would blow westward. However, prior research found that Titan's winds do blow eastward at altitudes above about 3 miles (5 km). This finding has led scientists to wonder if these high winds might somehow help solve this puzzle, even though they blow far above these dunes.
Now, researchers have found that rare methane storms could help sculpt the moon's surface.
"Clouds and storms are rare on Titan," said Benjamin Charnay, a planetary scientist at the Dynamic Meteorology Laboratory in Paris and lead author of the study detailing the new findings. "They were not expected to have an impact on dunes."
Sand dunes on Saturn's largest moon Titan dominate
this image captured by NASA's Cassini spacecraft in 2009. This image is
centered on a region just north of Titan's equator. Scientists suspect
Titan's giant dunes at the equator may be sculpted by intense methane
storms.
Credit: NASA/JPL-Caltech/ASI
Credit: NASA/JPL-Caltech/ASI
Computer models of weather on Titan revealed that methane clouds can reach altitudes of 15.5 miles (25 kilometers), where the high, fast eastward winds blow. The researchers found that, as a result, methane storms can produce downdrafts that flow eastward on strong gusts after they reach Titan's surface.
The researchers estimated that these eastward gusts can reach up to 22 mph (36 km/h) — 10 times faster than the usual winds close to Titan's surface.
"We were very surprised by the intensity of the storm gusts," Charnay said. "For Titan, it is like a hurricane."
The researchers suggested that these storm gusts may explain the shape, size, spacing and eastward growth of Titan's dunes. If scientists can get a better understanding of how these dunes form on Titan, it could reveal more insight into the moon's present and past atmosphere.
"There are long dunes on Titan which formed over a very long period of time, likely more than 1 million years," Charnay said. "Others are shorter and formed during the last 100,000 years."
By studying Titan's dunes, scientists can also learn more about dune formation on Earth. For example, in this new study, the researchers developed a new growth mechanism for dunes that may answer questions about how dunes form on Earth, Charnay said.
The scientists detailed their findings online April 13 in the journal Nature Geoscience
News
SpaceX Dragon cargo ship reaches space station
Italian astronaut Samantha Cristoforetti, working inside the windowed cupola module, nosed the outstretched crane to Dragon’s grapple fixture and snared the capsule at 6:55 a.m. EDT/1055 UTC as the station sailed about 260 miles over the Pacific Ocean just east of Japan.
Dragon, loaded with more than 4,300 pounds of food, clothing, equipment and science experiments, blasted off aboard a SpaceX Falcon 9 rocket on Tuesday, the sixth of a recently extended 15-flight contract with NASA to run cargo to the station.
This time, Dragon’s unpressurized trunk, which typically holds experiments and instruments installed outside the station, is empty so that the pressurized section could be stuffed full. The cargo includes:
*A replacement nanosatellite for Planetary Resources, an aspiring asteroid mining outfit that lost its Arkyd 3 technology demonstrator during Orbital ATK’s botched Antares launch in October. Comprised of three CubeSats, Arkyd 3 will be deployed from the station’s Kibo module by NanoRack’s satellite launcher.
*14 Earth-observation CubeSats, called Doves and owned by San Francisco-based Planet Labs.
*20 mice that will serve as subjects for an experiment investigating how microgravity impacts bones. The rodents will be euthanized and dissected in orbit, and the samples sent back to Earth when Dragon returns in May. The Rodent Research Facility made its debut flight to the station last year. The bone loss study is sponsored by Novartis under a commercial agreement with the Center for the Advancement of Science in Space, which manages station research under a U.S. National Laboratory program.
*A synthetic muscle material developed by Ras Labs, a Massachusetts Institute of Technology spinoff company that wants to test how radiation impacts the electroactive polymer. The material contracts with an electric current and expands back to its original state when the charge is reversed.
Initial ground-based experiments show the materials are resistant to radiation, said lead researcher Lenore Rasmussen. For their debut space run, the materials, which have different additives and coatings, will be attached inside the station and photographed over the next three months. They will be returned to Earth for analysis.
*An Italian-made espresso machine called “ISSPresso” specially modified to work—or hopefully work—in the challenging conditions of zero gravity. A joint project of Argotec, Lavazza and the Italian Space Agency, the machine, which will be attached to a wall with bungee cords, was modified to fit the station’s standard-size water pouches.
“We have been thinking about taking the espresso into space for some time,” Lavazza vice president Giuseppe Lavazza said in a statement. “We hope (it) will improve the living and nutrition quality of astronauts engaged on long missions.”
Dragon also is carrying food, clothing and care packages for the astronauts; dozens of experiments, including studies devoted for the station’s first year-long crew; environmental control and life support equipment; computers and other electronics; photo and TV gear; and components for the U.S. spacesuits.
The capsule is expected to remain in orbit until May 21.
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