Pluto may be geologically active


Photo: NASA

Contrary to the grand old theory that Pluto is an inert mass made up of rock and ice water, data returned by NASA’s New Horizons mission hint that Pluto may well be geologically active.

Geological activity on Pluto has been proposed to explain how its atmosphere remains flush with nitrogen despite the gas escaping in huge quantities. Based on initial data returned by New Horizons, it became clear that the surface of Pluto was not riddled with impact craters, and the dwarf planet had many smoothened surfaces. These indicated geological activity on its surface.

Nitrogen gas dominates Pluto’s atmosphere despite hundreds of tons of atmospheric nitrogen escaping into space every 60 minutes; the Sun’s ultraviolet light heats Pluto’s atmosphere causing the nitrogen gas to escape. Besides being found in the atmosphere, nitrogen is also present in the form of ice that moves around the dwarf planet’s surface in seasonal cycles.

So where does the planet get its nitrogen from? In a paper published recently in the journal The Astrophysical Journal Letters, Kelsi N. Singer the first author from Southwest Research Institute, Colorado, U.S. considered several likely sources.

For instance, they found that comets could not have delivered enough nitrogen mass to resupply the nitrogen escaping from Pluto’s atmosphere. The nitrogen mass delivered by comets will be “three-to-four orders of magnitude less than what is lost from the atmosphere,” the researchers found.

Similarly, craters made by comets crashing on to Pluto could not have excavated sufficient amount of nitrogen present in the near-surface reservoirs to compensate for the loss.

Since surface ice is not uniformly distributed over the surface of Pluto, nitrogen must be present to a large depth. To release this nitrogen, large craters must have impacted Pluto to create very big craters and such craters would have been in large numbers. The researchers concluded that excavation from catering falls “short by an order of magnitude or more.”

Also, sublimation of nitrogen through carter floors and walls cannot account for the loss of atmospheric nitrogen.

This leaves only two other options — either the amount of nitrogen escaping from the atmosphere was less in the past or Pluto is geologically active and hence able to resupply or compensate for the loss from the atmosphere.

“We suggest that either atmospheric escape rates have been overestimated or cryovolcanism or another tectonic or geodynamic means of nitrogen resupply may be necessary to resupply Pluto’s atmosphere against escape and the build-up of an in volatile lag deposit,” they write.

There is no way of determining the geological activity in Pluto. One has to wait for the images from New Horizons to confirm the presence of geological activity.

Published in The Hindu on August 17, 2015