Under the "heart" of Pluto can hide the ocean of liquid water

Pluto is one of the most distant and coldest objects of the Solar System of those that are relatively well studied by man. The surface of the dwarf planet is covered with nitrogen and methane ice interspersed with water ice. Pluto may have nitrogen seas and cryovolcanoes. In general, this icy world is not at all dead. Certain geological processes take place here, the surface of the dwarf planet is not static.

Recently, two teams of researchers published the results of the analysis of data transmitted by the New Horizons probe to Earth. Scientists studied, in particular, the most visible object on Pluto - Sputnik Planitia. As it turned out, this region is interesting not only by its shape.

Sputnik Planitia itself is a huge depression filled with nitrogen ice. This ice is more dense than water ice, so the latter lies on the surface of frozen nitrogen. Experts say that huge arrays of frozen water ice have been found in this place. And they are not static, but move. This whole region is dynamic, its surface moves, the individual layers are mixed. Perhaps the reason for this is Pluto’s radioactive nucleus, which warms up the overlying layers.
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Experts talk about even more interesting things. In their opinion, the region itself should not exist in this particular place. The fact is that Pluto and Charon, his satellite, are connected by tidal phenomena. Pluto is always addressed to Charon by one side. And on the back is Sputnik Planitia. If you draw a straight line through the centers of Charon and Pluto, then this line will cross the described region. The chances that the region was formed in this place are very small. Everything suggests that both the plateau and Charon are on a single "tidal axis."


The dynamics of the position of the "heart" of Pluto. Source: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute

But gravitational mechanics can explain everything. As a result of tidal phenomena arising from the interaction of Pluto and Charon, the dwarf planet could simply turn to the other side of Charon. If the surface of Sputnik Planitia were less dense than the rest of the surface of the icy planet, this region would become the north pole, just as the least dense region of the moon would become its south pole. But if we assume that Sputnik Planitia is denser than the rest of the surface of Pluto, then everything falls into place - in this case, the region should be exactly where it is located now. The most interesting thing is that this particular object could cause the displacement of the axis of rotation of Pluto by 60 degrees. Sputnik Planitia was formed, most likely in the northern hemisphere opposite Pluto’s side from Charon.

The gravitational interaction of two dwarf planets is a significant influence factor that changes the voltage of the upper layers of Pluto and affects its axis of rotation.

Here the second team of scientists revealed a discrepancy. The fact is that nitrogen ice in Pluto conditions is really denser than water ice. But still, this is not enough to deploy a dwarf planet. Both teams of scientists have calculated that for this purpose the thickness of the nitrogen ice should reach 50 km. But in fact, the thickness of the region’s ice crust is no more than 5 km.



But what then could be the reason why Sputnik Planitia is now exactly where it is? Perhaps the reason is that there is a liquid ocean beneath the ice. If this is true, then this ocean has made the ice crust thinner. Most likely, this ocean is not methane or nitrogen, but liquid water, which has replaced a significant part of the ice. And since liquid water is heavier than ice, which it replaced, then it became the cause of the rotation of Pluto. Repeated analysis of the data showed that the thickness of ice over the ocean of liquid water can be 7 kilometers.

The ocean under the surface of Pluto, experts say, is different from Europe’s subglacial ocean or the Earth’s oceans. The water here is extremely salty, it is saturated with nitrogenous compounds.

Water is an important factor influencing the offset of Pluto around the axis of its rotation. But the nitrogen ice, located on the surface of Sputnik Planitia, is also very important in the dynamics of the rotation of the dwarf planet. More precisely, it is important the amount of nitrogen ice in this place. And it changes due to temperature fluctuations, the most active changes occur when Sputnik Planitia is closer to the equator. All this creates the likelihood of the existence of a complex cycle of changing the position of Pluto. “If volatile substances (for example, nitrogen) leave Sputnik Planitia as part of seasonal changes, this may be the cause of small fluctuations of the planet,” the authors conclude.


Possible way of formation of this region. Source: James Tuttle Keane

How did the "heart" appear? A hypothesis has already been reported earlier, according to which billions of years ago, an object moving at tremendous speed crashed into Pluto and left an eternal reminder of itself on the planetoid - a crater 825 kilometers wide. But instead of turning into an ugly scar on the body of a dwarf planet, the crater transformed into an unusual object that reminds us, people, of an icy heart.

The area of ​​the crater is about a third of the surface of Pluto. The ice field Sputnik Planitia is located just within the impact crater. Water ice may give the region a white color.

DOI: 10.1038 / nature20120 , 10.1038 / nature20148