For billions of years a thick blanket of relatively inert nitrogen ice had protected the highly reactive layers below.

Winds of 200 miles an hour could then carry the shower of nitrogen ice in plumes extending up to 30 miles wide and 45 miles long.

In the process, some of Pluto's nitrogen ice has evaporated off its surface into the atmosphere.

For one thing, the ethane apparently does not exist as individual grains but is dissolved within the much more plentiful nitrogen ice on Pluto's surface.

Charon doesn't have the inconvenience of an atmosphere, or an overlay of nitrogen ice over the water.

That depends more on surface temperature, which determines how much of the Plutonian methane and nitrogen ice turns into gas.

Triton may have large, seasonal polar caps of smooth nitrogen ice underlying layers of dark organic materials.

But its cyrogenic cooling system ran out of solid nitrogen ice in less than two years, much sooner than expected.

Detection of more such volcanoes, which spew nitrogen ice and gas 5 miles high and 90 miles downwind, was announced at the news conference.

They found a cold dark world of nitrogen ice wandering amongst the stars; there were millions of such worlds cast adrift.