Here on Earth, the common notion is that a lake is a body of water surrounded entirely by land. But imagine a lake on Saturn's largest moon, the Titan. The planet itself being so far away from the Sun, it comes as no surprise that the temperature there would be much lower. On Titan, it is 90 degrees Kelvin, in fact.

Surely, this has an effect on the kind of elements present there. If you are to think that nothing else but a body of water can be a lake, then you are highly mistaken. Because on Titan, over 75 lakes ranging in size from about a mile and a half to 40 miles across have been detected, and they are not filled with water. Instead, cradled in the lakes as liquid is methane. Here on Earth, it is a form of gas. But out there, it's clearly liquid.

Dr. Ellen Stofan of the Proxemy Research in Washington DC, as well as a member of the Cassini Radar team explains this as being caused by the really low temperature on the moon. They also believe that the lakes have another kind of hydrocarbon compound of some sorts in them, called ethane.

Interestingly enough, although the chemistry is apparently different on Titan, the lakes' behaviour do resemble their Earthly counterparts. Says Stofan, "The methane-ethane would become transparent, the way water is on Earth, it would be behaving like water, the lakes could have small waves on the surfaces." What also got them into thinking that these are, in fact, lakes is the way that other channels feed into then, their shapes, shorelines, and all of those geological aspects of the lake.

The team's discovery is featured in this week's journal "Nature".

The next time you start asking about how life on Earth started out, don't be surprised if researchers don't talk about their most recent archaeological dig, but instead say something in the lines of looking to the heavens. Naah, they haven't turned to Astrology.

We've already mentioned in an earlier article that it's been recently discovered that Titan, one of Saturn's moons, has large methane deposits circulating in a very similar manner as the winds and rivers on Earth. It turns out that organic particles, created by sunlight interacting with the Titan's methane-laden atmosphere, may provide clues to what earth was like 3.6 billion years ago, when primitive life was only beginning to exist.

Taking a cure from this recent observation by the NASA-ESA Cassini-Huygens mission, scientist Margaret Tolbert and her colleagues over at the University of Colorado pulled off this experiment to replicate the conditions that occur on Titan. They irradiated a methane cloud with UV rays, and then injected it with CO2 gas to see what would happen. Sure enough, the resulting reaction created a haze of organic molecules very similar to that on Titan - molecules that were digestible for early life on earth.

"That would have been a food source for any budding life," Tolbert said regarding the results. "And it would have been, importantly, a global food source. And so life, instead of being confined to certain very special environments, could have thrived in every puddle."

Radar on NASA-ESA's Cassini-Huygens mission shows that Titan might actually be earth's closest analog within the solar system.

Titan, Saturn's giant moon is beyond ice cold. At a temperature of 93 Kelvin, it has an atmosphere filled with methane. At first glance, Titan hardly resembles earth. The thing is, Radar readings from Cassini show dark regions with clear borders near the pole. A possible explanation for this low radar reflectivity is that the areas could be large bodies of liquid. Yep. Lakes. Dark areas have been detected before but none with contrast as 'dramatic' as this.

Professor Jonathan Lunine says that, "these data are showing us that methane does sit on the surface in lakes, it does get dumped by big methane thunderstorms, it does carve rivers and streams (although not as often perhaps as on Earth), and it does undergo chemical reactions that produce other organic compounds."

It would be like taking terrestrial geological processes and swapping out the chemicals and temperature, and having the same kind of rivers, rains, lakes, aeolian (wind-driven) processes, volcanism, tectonism, impact processes. It's basically the lexicon of Earth-like geological activity with different materials. In Titan's case, methane instead of water. Titan's surface would be active in a lot of ways than Earth's is.

This added to the speculation that there may be terrestrial life on Titan, which only makes the frozen moon seem all the more like a second earth. Titan, pseudo-Earth, nice possibility isn't it?

An ion engine operates by removing electrons from atoms of a gas – usually xenon – and then accelerating the resulting ions through an electric field. Thrust is created as the ions are shot out the back of the engine and it could have enough kick to send a spacecraft all the way to Titan, Saturn's giant moon, more than 1 billion kilometres from the Sun. Ion engines are also more fuel efficient than conventional rockets while providing a steady source of propulsion that makes it ideal for spacecrafts designed to fly to the outer solar system.

In 1998, NASA tried out ion engines on its Deep Space 1 mission, which headed for an asteroid and a comet 203 million km from the Sun. But the NSTAR engines used during the mission were not powerful enough for more distant journeys. NASA's new Evolutionary Xenon Thruster (NEXT) can generate 236 milliNewtons (6.9 kilowatts) of engine power. That is 2.5 times as much thrust as the NSTAR engine and enough for longer space trips. NEXT is also more powerful than the 22 mN engines on Japan's Hayabusa spacecraft sent to asteroid Itokawa and the 70 mN engines on the European Space Agency's SMART-1 lunar probe.

Like NSTAR, NEXT uses xenon gas as its propellant and solar arrays to capture energy from sunlight but it provides more thrust than previous ion engines. It can also throttle down to lower levels as it travels farther from the Sun and receives less sunlight. This power efficiency allows it to operate at greater distances than NSTAR.

The first NEXT engine has passed NASA's preliminary tests and now faces new tests that will determine how well it holds up to extremes of temperature it may experience in space. NASA hopes to have engine testing completed by September 2007, so that NEXT could be considered for future missions to send an orbiter and a lander to Titan or possibly Jupiter.

NASA's Cassini spacecraft sent back images from Saturn's giant moon and scientists are almost sure the black patches near the pole are lakes. They think the dark patches could have been caused by Cassini's radar beam hitting very smooth surfaces, most probably liquid methane or ethane, on Titan's surface.

If the scientists are right, Titan is only the second body known to have liquid surfaces. The lakes are thought to be filled by rainfall and even seasonal storms, which are part of Titan's methane cycle.

The largest lakes are around 62 miles (100 km) across, although there is also a network of smaller, interconnected lakes said to resemble parts of Finland and Canada. Some appear to be deposits left behind as the methane lake evaporated. The lakes are more common near the pole probably because the temperature is cooler and the methane is less likely to evaporate. But since the temperature differences are small, lakes may exist at lower latitudes.

"When we have more coverage of the equator, we could see lakes there, too. We've only covered a few per cent of the surface so far," says Enrico Flamini of the Italian Space Agency in Rome.

"We could hope to see sea-surface textures due to waves diffracting around islands, or vortices in the wake of islands," says Cassini radar scientist Ralph Lorenz of the University of Arizona, US. "These sort of dynamic features would make liquids 'come alive'." While evidence of lakes is strong, the patches could turn out to be areas of soot, or dry lake beds. Imaging the areas again could show if the lakes grow or shrink or have waves.

Recent images taken by the Cassini spacecraft indicates that the highlands of Saturn's moon Titan may be riddled with caves.

The  Xanadu region of Titan is about 4000 kilometers (about 2500 miles) wide. While already though to be a highland area, Cassini's haze-penetrating radar shows that  the interior of the region is crossed by mountain ranges rising to a height of 1,000 meters (about 3,000 feet)  This contrasts with most of Titan's surface, which appears relatively flat.

"These are the highest mountains measured on Titan so far," says Cassini team member Ralph Lorenz of the University of Arizona in Tucson.

Radio waves bouncing off Xanadu indicate these mountains are not solid. They appear to have strange electrical properties – specifically a low "dielectric constant," which means they shouldn't be solid enough to stand.

"The only reasonable material makeup that could have a very low dielectric constant and still hold together enough to form the structures that we see would be some sort of porous stuff – most likely porous water ice," says another team member, Steve Wall of the NASA JPL in  Pasadena, California.

One theory is that the region is filled with caverns, possible carved out by the methane rain that is believed to fall on Titan.

Erosion from that rain would also form the long river valleys along the Xanadu region's edge. Cassini scientists theorize that these rivers carry ice grains down to the plains to form the dunes seen on much of Titan's surface.

There are also small, dark patches in this region. These may be methane lakes, although there little evidence of liquid still present on the surface. Evidence of liquid may be forthcoming, however.  This weekend, Cassini will take pictures of Titan's north pole, where lakes or seas to would be likely to exist, since the extreme cold would keep methane from evaporating into gaseous form.

You can view a Quicktime video of the the Cassini images here.

If you think angels can't be seen outside of this planet, then you're wrong. Sort of.

An image of the two largest moons of Saturn together was taken by the Cassini spacecraft last June 11 where it shows that the smaller moon was wearing a halo. This was captured when Cassini was about 3.6 million kilometers away from the moon Rhea.

The second-largest moon of Saturn (Rhea) is the one silhouetted again the moon Titan in the image. Titan is about three times as large as Rhea. The halo effect is actually the sunlight scattered by the thick atmosphere of Titan. (The sun is positioned behind the moon in this image.)

This image however, was not taken for its aesthetic appeal; this is going to be used by mission managers to aid them in planning out Cassini's manoeuvres in the coming years. These large moons have a gravitational effect on the spacecraft so it's important to gather such orbital information for the mission.

NASA's Earth Observing-1 spacecraft was designed to test imaging technology and collect large amounts of data, also filtering the information it collects to discard those that need not be downlinked to earth. The Autonomous Sciencecraft software ensures that scientists on Earth only receive the important data.

According to Steve Chien, principal investigator at NASA's Jet Propulsion Laboratory, ever since the decision-making software has been used on EO-1 last year, scientists are 100 times more likely to receive data that actually has valuable information for flood monitoring and for looking at freezing and thawing patterns.

Another benefit of the software is that it has reduced mission costs from $3.6M per year to $1.6M per year.

Because of the benefits the implementation of the Autonomous Sciencecraft has rendered, Onboard Autonomous Science Investigation System principle investigator Rebecca Castano hopes the software can also filter data being collected by the Mars rovers and Mars Odyssey missions.

The same software may help home in on rare and seasonal Mars events such as dust devils and cloud dusts. It will also increase to 90% the rover's success rate of finding a rock worthy of study.

Autonomous Sciencecraft can also aid future study of Saturn's moon Titan. According to Ralph Lorenz, an assistant research scientist at the Lunar and Planetary Laboratory at the University of Arizona, since Titan is so far away from Earth, communications with an aircraft will be extremely difficult. But the software "could help position whatever aircraft would be used, such as some sort of hot air balloon-type device, in an area likely to produce profitable samples."