Lost lakes of Titan are found at last

This colorized radar view from Cassini shows lakes on Titan. Color intensity is proportional to how much radar brightness is returned. The colors are not a representation of what the human eye would see. Image credit: NASA/JPL/USGS

Lakes of methane have been spotted on Saturn's largest moon, Titan, boosting the theory that this strange, distant world bears beguiling similarities to Earth, according to a new study.

Titan has long intrigued space scientists, as it is the only moon in the Solar System to have a dense atmosphere -- and its atmosphere, like Earth's, mainly comprises nitrogen.

Titan's atmosphere is also rich in methane, although the source for this vast store of hydrocarbons is unclear.

Methane, on the geological scale, has a relatively limited life. A molecule of the compound lasts several tens of millions of years before it is broken up by sunlight.

Given that Titan is billions of years old, the question is how this atmospheric methane gets to be renewed. Without replenishment, it should have disappeared long ago.

A popular hypothesis is that it comes from a vast ocean of hydrocarbons.

But when the US spacecraft Cassini sent down a European lander, Huygens, to Titan in 2005, the images sent back were of a rugged landscape veiled in an orange haze.

There were indeed signs of methane flows and methane precipitation, but nothing at all that pointed to any sea of the stuff.

But a flyby by Cassini on July 22 last year has revealed, thanks to a radar scan, 75 large, smooth, dark patches between three and 70 kilometers across (two and 42 miles) across that appear to be lakes of liquid methane, scientists report on Thursday.

They believe the lakes prove that Titan has a "methane cycle" -- a system that is like the water cycle on Earth, in which the liquid evaporates, cools and condenses and then falls as rain, replenishing the surface liquid.

As on Earth, Titan's surface methane may well be supplemented by a "table" of liquid methane that seeps through the rock, the paper suggests.
Some of the methane lakes seem only partly filled, and other depressions are dry, which suggests that, given the high northerly latitudes where they were spotted, the methane cycle follows Titan's seasons.
In winter, the lakes expand, while in summer, they shrink or dry up completely -- again, another parallel with Earth's hydrological cycle.
The study, which appears on Thursday in the British weekly journal Nature, is headed by Ellen Stofan of Proxemy Research in Virginia and University College London.
Titan and Earth are of course very different, especially in their potential for nurturing life. Titan is frigid, dark and, as far as is known, waterless, where as Earth is warm, light and has lots of liquid water.
But French astrophysicist Christophe Sotin says both our planet and Titan have been sculpted by processes that, fundamentally, are quite similar.
The findings "add to the weight of evidence that Titan is a complex world in which the interaction between the inner and outer layers is controlled by processes similar to those that must have dominated the evolution of any Earth-like planet," Sotin said in a commentary.
"Indeed, as far as we know," Sotin added, "there is only one planetary body that displays more dynamism than Titan. Its name is Earth."

(c) www.physorg.com

Danger? Nanotube-Infested Waters Created in the Lab

 

Carbon nanomaterials can mix in water despite being hydrophobic, raising the possibility of a spreading spill in the future.

Carbon nanotubes--and their spherical cousins known as buckyballs--are proving to have myriad uses, finding employ in improved solar cells, electronics and medical probes. But the production volume of the tricky nanomaterials remains nanoscale when compared with the production volume of other industrial components. Nevertheless, environmental engineers have begun investigating how such materials might interact with natural environments if accidentally released and have discovered that at least some of the hydrophobic (water fearing) materials persist quite readily in natural waters.
Jae-Hong Kim of the Georgia Institute of Technology and his colleagues investigated how so-called multiwalled carbon nanotubes--layered, straws-within-straws of carbon atoms--interacted with natural water, in this case samples taken from the nearby Suwannee River. To their surprise, the carbon nanomaterial did not clump together as it tried to avoid water molecules, rather it interacted with the negatively charged natural organic matter in the river water. This organic matter seemed to shield the nanotubes and allow them to disperse throughout the water after an hour of mixing, instead of clumping and settling. "At the beginning, the solution is very black and, over time, it becomes grayish," Kim says. "What is interesting is that it is still grayish after a month." In other words, the nanotubes do not settle even after this time period.
This monthlong suspension means that Suwannee River water was actually better at promoting the dispersal of carbon nanotubes than chemical surfactants, which can maintain nanotubes in solution for roughly four days, according to the paper presenting the finding published online in Environmental Science and Technology. Similar studies with buckyballs--stable balls of 60 carbon atoms, also known as C₆₀--had required copious organic solvents in order to maintain suspensions.

Because of the presence of such solvents, toxicity tests on C₆₀ have been open to question as to whether the buckyballs or the solvents caused the damaging effects. Environmental engineers Volodymyr Tarabara and Syed Hashsham of Michigan State University and their colleagues tested the toxic effects of such buckyballs in water--without solvents--on lymphocytes, human immune cells. The researchers created solutions of C₆₀ and water using ethanol at levels previously proven to have no toxic impact and using weeks worth of magnetically powered stirring.
At concentrations as low as 2.2 micrograms per liter, the clumps of C₆₀ damaged the DNA of the immune cells, according to microscopic analysis presented in the December 1 issue of Environmental Science and Technology. The exact mechanism by which C₆₀causes the DNA damage remains unclear, particularly because imaging could not detect the smallest of the buckyball clumps, but its DNA damaging effect was dose dependent. "We are not sure if very very small particles exist, one or two nanometers big," Tarabara says. "They may be very important as far as cellular damage."
Regardless, such nanopollution is unlikely to occur anytime soon: "The fact of the matter is that it takes weeks of mixing to generate appreciable concentrations in the size range where the particles are small enough not to settle," Tarabara notes. "It's not something that we can expect to be out there loose." But the environmental engineers argue that such research should be carried out before any widespread adoption of the new carbon nanomaterials takes place, especially because they seem to have a few surprises in store. "One thing is definite," Kim says, "these materials were not traditionally considered an aqueous-based contaminant." He adds: "I am saying, 'Well, it seems possible.'" --David Biello

[source: www.sciam.com]