Serenity Chasma: A Window to Charon and its Past

Charon Valley May Tell a Tale of Primordial Oceans

I have to say, the New Horizons mission is really the planetary exploration gift that keeps on giving! Every week the mission team drops some more amazing science on us.  This week, the scientists are sharing an image with us that may be evidence of an ancient ocean on Pluto’s largest moon (and orbital companion) Charon. It’s a valley on the icy surface called Serenity Chasma.

Serenity appears to be a tectonic fault that was formed when something pulled the surface apart. You see similar places on Earth, where the crust cracked open and formed a valley or a scarp. On Charon, these formed when the surface cracked as the subsurface part of the moon expanded as it froze. To understand this, take a look at Charon’s structure. Its upper layer is mostly water ice. When this moon was a young’un, it was still being heated from within by the heat that built up as it formed. Also, radioactive elements inside this moon supplied heat as they decayed. This is called radiogenic heating and is a well-known heat source for many places in the solar system. Inside of Charon, this heat could have kept the interior ices slushy and even liquid for quite a while.

However, all good things must come to an end. And, as happens with worlds as they cool down, Charon’s heat dissipated and that caused the interior ocean and the surface to freeze. When water ice freezes, it expands. That must have pushed the surface outward. Since water ice is pretty brittle, it cracked, forming the valleys we see today. That’s the best geological explanation for the valleys that seem to cross the surface of Charon, giving us more fascinating peeks into the ancient past of the most distant worlds in the solar system explored to date.  The spacecraft, which is on its way to an encounter with another Kuiper Belt object in a few years, is slowly sending back all the data it collected when it swept past the Pluto system in July 2015.

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