Scientists with the Cassini-Huygens mission have just announced they identified a river on Saturn’s moon Titan. The river appears in radar images taken in September of this year by the Cassini spacecraft, a joint project run by NASA and the European and Italian Space Agencies.
The extraterrestrial river extends 250 miles through the moon’s north polar regions before it drains into a large sea called the Ligeia Mare. Since the river’s course is relatively straight, scientists say it likely occurs along a fault line.
The river valley appears dark in the radar image—an indication of a smooth surface—so scientists suggest the river is actually flowing. The liquid between its banks isn’t water, though. In contrast to Earth’s water-based hydrologic cycle, Titan’s cycle operates instead on hydrocarbons such as ethane and methane. Titan is the only other world scientists know to have stable liquid on its surface.
Image courtesy of the European Space Agency.
An illustration of the descent
While the Cassini probe has been taking the gorgeous pictures of Saturn we know and love, its little buddy and traveling companion, the Huygens lander, has been on the surface of the moon Titan. A just-published reconstruction of what happened when Huygens hit Titan’s surface eight years ago gives insight into what the ground on the methane-soaked body is like: something like damp sand, or perhaps crusty snow.
Cassini image of a landslide on Iapetus
Landslides can wreak enormous destruction, especially when they travel farther than expected. When an avalanche occurs, dirt both falls vertically and spreads horizontally, with the horizontal distance usually no more than twice the vertical drop. But in a sturzstrom, some unknown factor decreases the coefficient of friction, allowing the earth to slide much farther; it acts more like a glacier or a lava flow than a regular avalanche. Theories about that friction-reducing factor abound—trapped air, water, or mud, pressure, rubbed and heated rock becoming more slippery, rock nanoparticles, sound waves, changes in local gravity—but its true nature is still unknown. By examining sturzstroms that occur on distant planets and moons—whose forces of gravity, atmospheres, fluids, and soil differ from those on Earth—researchers hope to unravel the factors that contribute to a landslide’s length. This information could help us predict landslides’ shapes and alleviate the damage they cause.
Artist’s rendering of AVIATR flying on Titan.
Saturn’s moon Titan is a lot like Earth: it has rain, seasons, volcanoes, and maybe even life. Well, it’s not exactly like Earth: the rain is liquid methane, the volcanoes spew ice, and any life would be based on methane. But still, it’s an interesting and relatively Earth-like place, considering the other planets and moons in our solar system. And University of Idaho physicist Jason Barnes says he has a perfect way to explore this moon: with a flying drone.
Why use a flying machine rather than the rovers that worked so well on Mars? With 1/7 the gravity but 4 times the atmospheric density of Earth, flying through Titan is 28 times easier than on our own planet. In fact, it’s the easiest place to fly in our entire solar system. Drones on Titan can be heavier while requiring less fuel. With these facts in hand, University of Idaho physicist Jason Barnes has proposed AVIATR, otherwise known as the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance.
What’s the News: NASA’s considering launching a boat from Earth, hurling it 746 million miles through space, and plopping it onto one of the minus-290 degrees Fahrenheit methane oceans of Titan. This mission to Saturn’s largest moon would the first of its kind to probe an alien ocean and—depending on the weather conditions—could be the first spacecraft to witness extraterrestrial rain. If the proposed mission beats out two other finalists, it could launch within the next five years. “Titan is an endpoint [in] exploring … the limits to life in our solar system,” project leader Ellen Stofan told New Scientist. “We’re going to be looking for patterns in abundances of compounds to look for evidence for more complex or interesting reactions.”
What’s the News: Images sent back from NASA’s Cassini spacecraft depict storm clouds and methane rain puddles, the first solid evidence of modern rainfall on Titan, Saturn’s largest moon. “We’re pretty confident that it has just rained on Titan,” lead author Elizabeth Turtle, from Johns Hopkins University Applied Physics Laboratory, told Wired. Astronomers have previous evidence of sulfuric-acid precipitation on Venus, but it doesn’t count as rainfall because it never reaches the surface.
What’s the Olds:
Not So Fast: Don’t read too much into these showers: Methane rain doesn’t mean life. The search continues.
Reference: “Rapid and Extensive Surface Changes Near Titan’s Equator: Evidence of April Showers.” E.P. Turtle, J.E. Perry, A.G. Hayes, R.D. Lorenz, J.W. Barnes, A.S. McEwen, R.A. West, A.D. Del Genio, J.M. Barbara, J.I. Lunine, E.L. Schaller, T.L. Ray, R.M.C. Lopes, E.R. Stofan. Science, Vol 331, March 18, 2011. DOI: 10.1126/science.1201063
Image: NASA/JPL/Space Science Institute
A new sight appeared on Saturn earlier this month: A massive, swirling storm with a tail that cuts across the gas giant. Amateur astronomer Anthony Wesley, who was the first to spot the Earth-sized scar on Jupiter last summer, took the first pictures of this storm. And then on Christmas Eve the Cassini spacecraft beamed home its own ravishing images.
The spacecraft took images of the planet on December 24th, returning — as usual — jaw-dropping pictures of Saturn showing the storm. This image, taken with a blue filter, shows the storm clearly. The main spot is huge, about 6,000 km (3600 miles) across — half the size of Earth! Including the tail streaming off to the right, the whole system is over 60,000 km (36,000 miles) long.
There’s an added bonus in these images: the shadow of the rings on the planet’s clouds is obvious, but the rings are nearly invisible! You can just make out the rings as a thin line going horizontally across Saturn in the first image. These pictures were snapped when Cassini was almost directly above the rings, which are so thin they vanish when seen edge-on. Actually, that works out well as otherwise they might interfere with the view of the storm in these shots.
For more details, check out the rest of Phil’s post at Bad Astronomy.
80beats: By Demolishing a Moon, Saturn May Have Created Its Rings
80beats: Mysterious Smash on Jupiter Leaves an Earth-Sized Scar
Bad Astronomy: Saturn rages from a billion kilometers away
Saturn’s moon Titan has lakes on its surface and a thick atmosphere, but there’s one more way this cold, distant world is like the Earth: It appears to have volcanoes—though they’re a little chillier than Eyjafjallajökull.
Scientists have long suspected and presented some evidence that Titan could have these features, and this week at the American Geophysical Union meet-up, researchers presented a finding from the Cassini spacecraft that they say is the best evidence yet of a Titanic volcano.
“We finally have some proof that Titan is an active world,” said geophysicist Randolph Kirk of the U.S. Geological Survey, who presented the findings. [NPR]
When the news comes from Saturn’s moons, the source is typically Titan—with its hazy atmosphere and frigid surface lakes of methane—or Enceladus—with its plumes of water ice. Last week, however, word came that Rhea, the second-largest Saturnian satellite, has some surprises of its own.
In Friday’s edition of Science, a study by Ben Teolis and colleagues confirmed that during a pass of the moon in March, when the ever-reliable Cassini spacecraft cruised over Rhea’s pole at an altitude of just 60 miles, it directly sampled tiny amounts of oxygen and carbon dioxide there.
“This really is the first time that we’ve seen oxygen directly in the atmosphere of another world,” said Andrew Coates, at UCL’s Mullard Space Science Laboratory, a co-author of the study. [The Guardian]
Hubble’s successor will be late, and over-budget. So concluded a NASA panel this week that investigate the James Webb Space Telescope, NASA’s next big thing, intended to survey the skies in infrared light with its 18-segment mirror. The word all along has been that James Webb would launch in 2014 at a cost of $5 billion, but the independent review (pdf) concluded that the earliest possible launch would be September 2015, and at a cost of more like $6.5 billion.
The report raised fear that other projects would be hurt. “This is NASA’s Hurricane Katrina,” said Alan P. Boss, who leads the subcommittee that advises NASA’s astrophysics program. The telescope, he said, “will leave nothing but devastation in the astrophysics division budget.” [The New York Times]
John R. Casani, who managed missions like Cassini and Voyager that are the picture of NASA success, led the panel. The technical side of the Webb telescope isn’t the problem, the report found–the management side is. The report faulted the management team for failing to make realistic estimates of the project’s costs and timetable, and further criticized NASA headquarters for not calling the managers on their impractical assessments.