Frozen ammonia discovered on Pluto might be a sign indicating the presence of liquid water underground, researchers from a range of institutions in the U.S. and one in France suggested in a study published in the journal Science Advances.

Researchers suspected that a reddish-brown crack, known as Virgil Fossa, was created by volcanic activity that had been driven by water.

Unlike the volcanic activity on Earth, which is driven by the planet's hot core and magma, a cryovolcano doesn't erupt with molten rock but with other material, such as water and ammonia.

According to the researchers, this means that it is probable that Pluto harbors liquid water under its surface.