It may be so far away that the Sun appears to be a particularly bright star it is sky, but it now seems that Pluto has a liquid ocean just beneath its icy surface, just as might have once been the case with its companion, Charon, billions of years ago.
Since passing through the Pluto-Charon system in July 2015, NASA’s New Horizons space craft has been returning the data it gathered at a steady rate, focusing initially on the high-resolution images collected during the probes high-speed run by the two tiny worlds (both smaller than the Moon). These images have revealed Pluto and Charon to be remarkably complex little worlds, with glacial flows, rotated ice blocks, volcano-like mounds and other features rivalling the geology found on much larger, warmer planets like Mars.
“What we see really has exceeded all of our collective expectations and imagination,” said William McKinnon, a planetary scientist at Washington University, Missouri, and one of those working on the project. “We think on the insides of these bodies were very cold ammonia rich oceans,” said McKinnon, noting that ammonia is a “fantastic antifreeze” that can lower the freezing point of water by 100 C.
Data from New Horizons indicate that Charon’s ocean probably froze solid around 2 billion years ago, expanding as it did so, cracking open the outer shell of the world. This freezing-out was likely due to Charon being too small to remain geologically active, its internal processes quickly slowing down as it cooled. Pluto, however, being larger, shows every sign of still being active and with a warm interior, so its subsurface ocean probably still exists, marking it as another in a handful of the solar system’s smaller bodies which are home to sub-surface oceans.
“We now have half a dozen worlds, like Enceladus (a moon orbiting Saturn), Europa and Ganymede (moons of Jupiter), and now Pluto, that seem to have oceans in their interiors,” New Horizons’ lead scientist Alan Stern said when discussing the potential and significance of Pluto’s ocean.
We know that life is remarkably tenacious and is extraordinary for surviving in unlikely places. All that is required is heat, a source of energy and water. On Earth, for example, volcanic fumeroles on the deep ocean floor can become havens for exotic life in places where sunlight never reaches.
This has led to speculation that places like Europa, which generates a lot of internal heat due to gravitational flexing thanks to the presence of Jupiter and the other large Galilean satellites, may well have similar, mineral-rich fumeroles on its ocean floor which may be havens for life exotic, basic forms of life. Could Pluto have the same?
“All we can say is that we think that Pluto has an ocean and we think that this ocean has survived to the present day. It’s the kind of ocean that is deep inside the interior of Pluto, in total darkness,” McKinnon stated.
“But, it would lie between a floating water ice shell and the rocky interior, so it would be in contact with rock. There would be a modest amount of heat leaking out. You certainly couldn’t rule it out, but anything about life on Pluto is simply speculation.”
Whether or not any basic life has managed to develop deep under Pluto’s icy crust is something we may never discover. However, that a liquid ocean does appear to exist beneath the planet’s icy shell is nevertheless intriguing. That water is present on Pluto has already been confirmed by the Ralph instrument suite aboard New Horizons. However, further evidence of its existence was revealed in February with the publication of images of “floating” hills of water ice on the nitrogen ice “sea” of Sputnik Planum”.
These hills are thought to be fragments which have broken away from the uplands surrounding “Sputnik Planum”. They exist in chains multiple kilometres in length or are grouped together, standing in stark contrast to the relatively flat expanse of the icy plain on which they sit.
Because water ice is less dense than nitrogen-dominated ice, scientists believe these water ice hills are like icebergs in Earth’s Arctic Ocean. In particular, the “chains” of hills have formed along the flow paths of the glaciers, while in the more “cellular” terrain of central “Sputnik Planum”, they become subject to the convective motions of the nitrogen ice, and are pushed to the edges of the cells, where the hills form clusters or groups. One of the largest of these, located towards the north of “Sputnik Planum” and measuring some 60km x 35km (37 mi x 22 mi) has been dubbed “Challenger Colles” in memory of the crew of the lost space shuttle Challenger.
Continue reading “Space Sunday: From Pluto’s ocean to Mercury’s darkness”
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