Eruption of ice volcano threw liquid water over the frozen surface of Pluto

Liquid water could once have existed on the frozen surface of Pluto, put there by the violent eruption of a cryovolcano, according to a new study.

“This was a huge surprise to all of us about Pluto,” planetary scientist Dale Cruikshank of the NASA Ames Research Center and an author of the paper told Science News. “It means there are lots of surprises waiting to be uncovered in that part of the solar system.”

The study used data gathered by NASA’s New Horizons mission in 2015. By analyzing the wavelengths of light in the images of Pluto’s surface, the team was able to see what chemical compounds are likely located on the planet’s surface.

Using this information, the scientists found signs of ammonia in areas of exposed water ice, clustered around a large crack in the surface of the planet called Virgil Fossa. The team believes this crack could have formed when liquid water erupted from a cryovolcano. As ammonia lowers the freezing point of water, it allows liquid water to exist even in Pluto’s frozen temperatures.

From the data, the scientists cannot tell whether eruptions happened regularly, or whether this was a one-off event. But they do know that the eruption would have been very dramatic, with water shooting from the surface into the atmosphere at 300 meters per second, before freezing and falling back to the surface as far as 200 kilometers (124 miles) from the eruption point.

A particular significance of the ammonia is that because it is relatively easily broken down by ultraviolet rays from the sun, the deposits must have been made relatively recently. Otherwise it would have broken down in roughly 400,000 to a billion years. “If you find [ammonia] at all, it suggests that it has been put there fairly recently,” Cruikshank said to Science News. “There is really no limit [to how recently], as far as I can see in the geology.”

This finding is important because although it has already been theorized that a liquid water ocean could exist beneath the icy crust on Pluto, this is the first evidence of water reaching the surface.

However, more research is required before scientists can be sure of whether cryovolcanoes do or did actually exist on Pluto. Further analysis of the New Horizons data and laboratory experiments to see how ammonia behaves in similar conditions could shed light on this mystery.

The findings are published in the journal Science Advances.