David Des Marais, who is an extraterrestrial-life expert at the American National Aeronautics and Space Administration, said the ocean had been identified as the fifth place in the solar system - including Earth - where primitive life might have evolved at some time in the past.
Europa, a moon of Jupiter, is also thought to have been hospitable for life at some point.
It is covered in thick ice, but scientists believe it might also possess an ocean of water deep under its surface caused by heat generated by the underground tidal forces resulting from its asymmetrical orbit.
Charon, which was discovered in 1978, is 2.6 billion miles away. It has a highly reflective surface, suggesting it too is covered in ice.
It also has an asymmetrical orbit and Nasa scientists believed this could also generate a warm environment for life to evolve, Dr Des Marais said.
"[Scientists] have done some theoretical calculations showing within the error of uncertainty there is the possibility that Charon could also be like Europa, although Europa seems more promising.
"When you look at this list of planets it is helpful to think of two lifestyles, one where life lives on the surface of the planet, which depends on solar energy, and then the type of biosphere that might live in the sub-surface, which does not necessarily depend on sunlight.
"These would be, for example, the candidates we would expect on Europa and Charon," he said.
"If you are going to mount a search strategy the first thing you look for is evidence of habitability rather than evidence of life. The interest in Charon is simply that the sort of outer orbital motion that gives kind of tidal stresses on Europa apparently also apply to Charon to some degree."