Pluto

planet, observatory

The planet that is not a planet.

Sand dunes may be found all over the world, including on the borders of lakes and seas, in deserts such as the Sahara Desert in Africa, and even underwater in the ocean. Robotic space missions have also discovered dunes on the planet Venus, the planet Mars, and Saturn’s massive moon Titan. Now that geologists believe they have discovered dunes on Pluto, they are scrambling for grant money to investigate the phenomena further.

In a place where the atmosphere is a wisp of air, not enough to generate the type of winds that are responsible for the formation of dunes in other parts of the Solar System, how can dunes form? Recent research theories suggest that these hypothetical dunes may be formed when methane ice crystals are lofted into Pluto’s thin atmosphere and somewhat pushed by the planet’s winds.

The Great Basin of Pluto, which is officially known as Sputnik Planitia, is the most well-known feature on the planet. When compared to the mountains that surround it, this area is incredibly smooth; nonetheless, when researchers inspected the high-resolution photographs obtained by the New Horizons spacecraft in 2015, they discovered intriguing wrinkles.

In other words, the putative dunes on Pluto do not seem to be the result of the same mechanisms that produce dunes on other planets in the Solar System, with one possible exception. Scientists studying photos of Comet 67P/Churyumov-Gerasimenko discovered something that seems to be dunes on the surface. Comet 67P does not have a true atmosphere, but it does produce jets of material that shoot out from the surface on occasion, which are visible from Earth.

Scientists suggest something similar for Pluto, which is comparable to what we already know.

Sputnik Planitia is built of ice, but not water ice; it is mostly composed of nitrogen, with traces of carbon monoxide and methane added for good measure. In this scenario, the methane ice sublimates (melts straight from solid to gas without first becoming a liquid), releasing tiny plumes of methane into the atmosphere when the Sun shines on Pluto’s heart. Therefore, the methane crystals are pushed into dunes by the minuscule amount of wind that blows as they fall back to the surface of the water.

To be honest, it’s possible that the creases on Pluto’s heart were not caused by sand dunes at all, but rather by some other mechanism (though scientists take care to rule out some other possibilities, like erosion). Despite this, the dune concept is entertaining, not least because it confirms the notion that dunes may grow on almost any item with a solid surface that contains grains that can be stacked on top of one another. Our inability to determine the height of these dunes, whether they move about, or if they developed thousands of years ago and remained in that state, keeps the debate roaring.

As a result, this little ice-ball seems to be geologically active, with probable volcanic activity as well as movable glaciers and now methane-ice dunes.

Scientists have discovered that the little, strange semi-planet on the outskirts of the investigated Solar System is hard to classify. But let’s back up a bit for the history of this obscure phenomena.

The American astronomer Clyde Tombaugh is credited with discovering Pluto in 1930. He built on the research of an earlier astronomer, Percival Lowell – who had spent over ten years scanning the night sky for the missing link of planets, and not finding it. What set Lowell going was the fact that astronomers had noticed both Uranus and Neptune had eccentric orbits that didn’t fit in exactly with what was known about celestial mechanics. In other words, they zigged when they should have zagged. This meant that something out beyond the two planets was exerting a gravitational pull on them, giving them a tipsy wobble. Lowell scanned the heavens bit by bit looking for a ninth planet, which was tedious and a deep strain on his eyes. What Tombaugh did was to take photographic plates of the same sections of the night sky, over and over again, and then have his assistants go through the plates to look for a phantom object that moved, that did not stay still in comparison to the stars around it. On February 18th, 1930, that object was found, and named Pluto, after the ancient Roman god of the underworld.

Tombaugh went on to reap numerous accolades for his discovery(though history remains silent about what, if anything, his assistants, who did all the grunt work, ever received for their part in the discovery.)

But in 2006 the prestigious International Astronomical Union put the kibosh on Tombaugh’s achievement by declaring that Pluto, though a nice and inoffensive enough object that circled the Sun with commendable regularity, was not, in fact, a real grown-up planet at all. They demoted it down to ‘dwarf planet.’ (After all, it IS smaller than our own Moon.) Why did they do this? Because of a rule they had just made that a planet, in order to be considered a planet, had to “clear the neighborhood around it’s orbit.” What that means is that to be considered a real planet an object orbiting the Sun must have enough gravitational pull to suck in all space dust and debris around it so that it is traveling a clear path. Pluto doesn’t do that. It is now considered to be just a part, although a big part, of the Kuiper Belt – a belt of asteroids that circles the Sun.

Still, the plucky little dwarf planet continues drawing a lot of interest. Those Plutonian dunes mentioned above rated a front page spread on Forbes.com. That’s better than most planets ever get!