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.
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: Astronomers have known for many years that Saturn’s moon Titan sports lakes of liquid methane. And in the past couple years, scientists have suggested that it also has an underground ocean composed of water and ammonia. Now, based on past observations by NASA’s Cassini spacecraft, astronomers are saying that Titan’s rotation indeed points to an underground sea—and where there’s water, there may also be life. “Our analysis strengthens the possibility that Titan has a subsurface ocean, but it does not prove it undoubtedly,” researcher Rose-Marie Baland told Astrobiology Magazine. “So there is still work to do.”
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
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]
It’s just a lab experiment, but University of Arizona researcher Sarah Horst says that her team’s re-creation of the atmosphere on Saturn’s moon Titan showed that atmospheric reactions could produce some of life’s basic ingredients, and do it without the presence of liquid water.
Titan, which is larger than Mercury, boasts a thick atmosphere of mostly nitrogen with dashes of methane, carbon monoxide, and other trace ingredients (At -290 degrees Fahrenheit, Titan is a tad too frigid for liquid water). Horst brewed up an approximation of that mixture. She and her colleagues then blasted it with radio-frequency radiation, a lab stand-in for ultraviolet radiation from the sun.
Carbonated oceans, moons torn apart, ring tsunamis—there’s a flurry of cool news about Saturn coming out of the American Astronomical Society’s Division for Planetary Science meeting in Pasadena, California.
The fizzy ocean of Enceladus
Saturn’s moon Enceladus is one of the prime candidates for some kind of life elsewhere in the solar system, thanks the the possibility that a large subsurface ocean feeds the plumes of ice and vapor that the Cassini spacecraft has spied blasting forth from the moon. At the AAS meeting in California, Cassini scientists Dennis Matson proposed something new about this extraterrestrial ocean: It could be carbonated.
Noncarbonated seawater circulating from the moon’s solid core to the surface would stall rather than seep though cracks in the ice because seawater is denser than the icy carapace. If the seawater were fizzy, however, gas bubbles would form in the liquid, reducing the ocean’s density. Once the seawater became less dense than the ice, the water could rise to within 10 to 15 meters of the frigid surface. That’s close enough to fill chambers in the icy crust with water that feeds the south polar plumes. [Science News]
Lake Ontario has some key differences compared to her equally-sized sister lake, Ontario Lacus: The Great Lake has water; Ontario Lacus has methane, ethane, and propane. The Great Lake invites sunbathers; Lacus’ beaches, almost ten times further from the sun, are icy cold. The Great Lake is located on Earth; Lacus on Saturn’s largest moon, Titan. Despite all these distinctions, new research points to an important similarity: liquid levels in both lakes change with the seasons.
From June 2005 to July 2009, the Ontario Lacus shoreline has receded by about 6 miles, Alexander G. Hayes and his coauthors report in two papers submitted to Icarus and the Journal of Geophysical Research. Looking at other lakes in Titan’s southern hemisphere, it seems they are dropping in depth by about three feet per year.
Despite its shoreline’s rapid retreat, there is little worry that Ontario Lacus and other Titan lakes will disappear forever. Scientists expect that the evaporation is just part of a cycle of evaporation and condensation, that changes with the seasons. The four years of observation, carried out by NASA’s Cassini spacecraft, represents only the period from about mid-summer to fall, since a Titan year lasts 29.5 Earth years.