Pluto is believed to contain a layer of water ice underneath another thin layer of frozen nitrogen. In addition, there is speculation that Pluto may contain a water ocean.
Little is known about Pluto compared to the other planetary bodies in our solar system, mainly due to Pluto's great distance from Earth. When the New Horizons spacecraft arrives at Pluto later in 2015, our knowledge of Pluto's make-up should increase significantly, including finding out about the presence of liquid water. If New Horizons finds an equatorial bulge, this would show that the water present is all frozen. If there is no bulge, liquid water could be present beneath the frozen crust, as liquid in a rotating spherical body pushes out toward the equator, causing ice to flow, evening out any bulging. Also, any surface fractures observed would indicate liquid beneath putting stress on the ice above it.