Exciting news from Cassini

The spacecraft Cassini has found water vapor on Saturn's moon Enceladus:

From a height of 109 miles, the Cassini spacecraft trained instruments on a cloud of water vapor venting from fissures at the moon's south pole.

From that moment, tiny Enceladus, only 310 miles in diameter, joined Mars and Jupiter's moon Europa as the solar system's leading candidates for having liquid water beneath their chilly surfaces -- a likely precondition for harboring life. But why the south pole? And how does something so small have liquid water? ...

Known before the Cassini mission as the brightest object in the solar system aside from the sun because of its shroud of crystalline ice, Enceladus is now also known as the smallest body to have active volcanism.

"What we think is happening is that jets of gas are escaping at substantial velocity from fissures to form a large column of gas above the south pole," Brown said. Mass spectrographic analysis showed that the gas is composed of water vapor, carbon dioxide, methane and maybe nitrogen, he added, and though temperatures at the vents are well below zero, liquid water will flash into gas when it is flushed into the vacuum of space.

Scientists were also able to confirm from these observations that Saturn's E ring, as suspected, is made of microscopic icy "smoke" from Enceladus's vents. What they have not been able to figure out is how there could be enough heat to make liquid water.

"Deep down, you have a reservoir of stuff -- liquid water mixed with carbon dioxide and light organics that is hot in a relative sense," Brown said. "Why, and why only at the south pole? Those are the big questions, and none of the explanations advanced so far is satisfactory."