The dwarf planet Pluto lies in the cold, dark outskirts of our solar system — the Kuiper Belt. At first glance, this would seem like a poor place to search for life. Nonetheless, NASA’s New Horizons spacecraft collected evidence that suggests Pluto possesses many of the characteristics required for life. It might even rank alongside more popular candidates for habitability, such as the icy moons Europa and Titan.

Despite decades of Earth-based observations, scientists knew little about Pluto until New Horizons studied it intensively, if only briefly, in 2015. The images it returned showed an unexpectedly diverse and active world, with mountains and rift valleys, glaciers of solid nitrogen, and a thin, hazy atmosphere.



Is it habitable?

Scientists typically assess the habitability of an environment in terms of the energy, organic molecules, and liquid water available. Pluto undoubtedly has the energy. Even before New Horizons, astronomers knew Pluto’s density well enough to deduce that it is roughly two-thirds rock and one-third ice by mass. Just like on Earth, radioactive decay within the rocks releases heat over geological time. This is Pluto’s dominant energy source, and it provides enough heat to warm the rocks in its interior close to their melting point. Other sources of heat, such as the gravitational energy released as the dwarf planet formed, are smaller but might contribute additional warming. Scientists don’t know whether the radioactive decay drives the kind of chemical interactions between water and rock we see at Earth’s midocean ridges, but it’s clear Pluto has substantial available power.

The dwarf planet also possesses organic molecules. The atmosphere contains about 0.3 percent methane. More importantly, New Horizons found that solar ultraviolet radiation splits these methane molecules apart and produces various simple hydrocarbons, including acetylene, ethylene, and ethane. Methane ice also appears on Pluto’s surface, as does a reddish material that is probably hydrocarbon haze particles settling out from the atmosphere. So the surface, at least, contains organic molecules that could provide the feedstock for life. Although it’s not clear there’s any mechanism to transport these molecules down to a possible ocean, studies of comets show that the interiors of outer solar system objects also can be rich in similar components.