Category Archives: Pluto

charon, New Horizons mission, Pluto

Serenity Chasma: A Window to Charon and its Past

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Charon Valley May Tell a Tale of Primordial Oceans

The side of Charon viewed by the passing New Horizons spacecraft in July 2015 shows a system of “pull apart” tectonic faults, which look like ridges, scarps and valleys—the latter sometimes reaching more than 4 miles (6.5 kilometers) deep. Courtesy New Horizons mission/JHU/APL.
The side of Charon viewed by the passing New Horizons spacecraft in July 2015 shows a system of “pull apart” tectonic faults, which look like ridges, scarps and valleys—the latter sometimes reaching more than 4 miles (6.5 kilometers) deep. Courtesy New Horizons mission/JHU/APL.

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.

New Horizons mission, Pluto

Pluto: The Gift that Keeps on Giving

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Nitrogen Glaciers on Pluto Studded with Water-ice Hills

Mountains on Pluto
This image shows the inset in context next to a larger view of Pluto’s encounter hemisphere. The inset was obtained by the Multispectral Visible Imaging Camera (MVIC) instrument on New Horizons.  The image resolution is about 1,050 feet (320 meters) per pixel. The image measures a little over 300 miles (almost 500 kilometers) long and about 210 miles (340 kilometers) wide. It was obtained at a range of approximately 9,950 miles (16,000 kilometers) from Pluto, about 12 minutes before the spacecraft’s closest approach to Pluto on July 14, 2015.
Courtesy NASA/JHU-APL, SWRI/New Horizons mission.

The King of the Kuiper Belt Objects continues to deliver its secrets, data bit by data bit as the New Horizons spacecraft slowly radios its mother lode of science from the July 14th flyby back to Earth. The latest thing it’s showing us is a series of chunky hills made of water ice. They ride along on the nitrogen glaciers that cover Sputnik Planum. That’s the ice plain that we see at the “heart” of the heart-shaped Tombaugh Regio.

How Do Water Mountains Form on Pluto?

Okay, so we know that nitrogen ice dominates Pluto’s surface.  So, how do water-ice mountains get into the picture? It turns out they’re jabbing up from the Planum because of the differences between the two types of ice that are there. Water ice is less dense than the nitrogen-rich ice. That means that, like the way ice cubes float in a glass of water or iced tea, the water ice mountains are floating in a sea of frozen nitrogen. They’re moving more like icebergs do in Earth’s Arctic Ocean.

The next question is, if they’re floating like icebergs, where do they come from? The nearby water ice mountains ringing the Planum may provide clues. “Chains” of these drifting hills get in the way of the surface glaciers as they flow. Eventually some of the hills enter the cellular terrain of central Sputnik Planum. That’s when the motion of the nitrogen ice takes over and pushes them out to the edges of the surface cell. What New Horizons is showing us are 20-kilometer-long ice mountain “ranges” being shoved around by the action of nitrogen ice. Imagine a 20-kilometer stretch of the Colorado Rockies or the Himalayas being pushed around to get an idea of the geological action taking place on Pluto.

This is all incredibly exciting — one year after New Horizons formally began its “close fly-by” mission operations, it’s telling an amazing story about this world that is, by all rights, one of the most interesting planetary bodies in the solar system.