What will we find when we finally visit Pluto?
Being almost 6 billion km from the Sun, the rock and ice-bound planet's surface must be terribly cold, colder than liquid nitrogen. Estimates place Pluto's surface at a cryogenically chilly minus 396 degrees Fahrenheit. That's cold enough for water ice to act like rock. But the warmer interior protected by miles of thick nitrogen, methane and carbon monoxide ices, and heated by radioactive rocks at the planet's core, may support a deep layer of liquid water-a Plutonian ocean. It's fun to speculate what life forms might have evolved in that Stygian sea.
Any future astronauts landing on Pluto will stand on the frontier of the solar system. They will see the dwarf planet's cratered moon Charon looming large in the sky. Inward, toward the Sun, our feeble home star will appear much like Venus does from Earth. There will be no warmth from its rays. Outward, the explorers will gaze into the immense gulf of interstellar space.
What's in the Sky: A full Moon occurs July 25 at 9:36 p.m. On July 27, look for the elusive planet Mercury at dusk in the west. Mercury is to the lower left of the star Regulus about 25-30 minutes after sunset. All you need are binoculars to get a glimpse of the hot little planet.
Lou Varricchio, M.Sc., is a former science writer at the NASA Ames Research Center in California. He is Vermont's NASA-JPL Solar System Ambassador and a recipient of the U.S. Civil Air Patrol's Gen. Chuck Yeager Aerospace Education Achievement Award.