Moon of the Week: Europa

A photo taken recently by the New Horizons unmanned spacecraft. Europa is one of Jupiter's Big Four moons (it has a whole mess of little ones). With a diameter of 1,900 miles it is close to the earth's moon in size. Covered with ice, and probably a liquid ocean underneath.

New Horizons is passing by Jupiter, then it uses the planet's gravity as a slingshot to send it to Pluto, where it will arrive in 2015.

(Photos from NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)