It's not that all those probes and rovers have been looking in the wrong place. The polar ice caps aren't part of the search range for signs of Martian water ('cause, doi, they're ice caps). But recent estimates by scientists from a joint-NASA Italian Space Agency experiment show that there's even more water than previously thought.

There's more ice down south than previously thought. Enough to cover Mars with a layer of water approximately 11 meters/36 feet deep. Hope you guys brought some swim bladders.

Says Jet Propulsion Laboratory's Jeffrey Plaut, "The south polar layered deposits of Mars cover an area bigger than Texas. The amount of water they contain has been estimated before, but never with the level of confidence this radar makes possible." These calculations were conducted with readings off the European Space Agency's Mars Express' radar system, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS).

This discovery is part of the research into the geological (and potential biological) history of the Red Planet, however. Along with those aquifers and the occasional breakout of Martian acne water, researchers try to discover if Mars had ever supported life in the past - and how all that water ultimately retreated underground and to the poles.

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.