Nine things we learned this week about the puzzling world of Pluto

There seemed to be little room in the UK press this week to cover the five new papers published by the journal Science, containing more data from the New Horizons flyby past Pluto last summer. It’s a shame, as the findings are pretty spectacular.

Alan Stern, New Horizons principal investigator from the Southwest Research Institute in Colorado, told “These five detailed papers completely transform our view of Pluto – revealing the former ‘astronomer’s planet’ to be a real world with diverse and active geology, exotic surface chemistry, a complex atmosphere, puzzling interaction with the sun and an intriguing system of small moons.”

The papers cover the geology and surface compositions of Pluto and its moon Charon, the atmosphere of Pluto, and some of the other satellites surrounding the dwarf planet, but with more data on the way from New Horizons, do leave some questions unanswered.

Here are the nine things we learnt from the data that we think are pretty cool:

1. Pluto’s heart is a basin of frozen ice, but is slowly beating away


Enhanced imagery taken by the spacecraft show that on the surface of Pluto, where there appears to be a heart, is actually a vast, icy, basin that is slowly churning away, continually melting and refreezing.

This smooth, 1000 km-wide plain, known as the Sputnik Planum, is thought to be powering much of the planet’s geological activity as its glaciers slowly circulate giant, buoyant ice crusts through the surrounding terrain.

2. Pluto may have volcanoes that spew water and are covered in sharp blades of ice

CGI IMAGE: Cryovolcano on Saturn's moon, Enceladus.(Photo Credit: © BASE Productions/ Sauce)
An artist’s impression of a cryovolcano (Photo Credit: © BASE Productions/ Sauce)

Around the edges of this icy basin the researchers have also spotted giant mountains of rock with deep, central depressions, thought to be spewing out ice and water from below the surface of the planet. These potential cryovolcanoes also feature large, sharp, jagged blades of ice jutting from their ridges, so although they may not be pouring out fire and molten rock, they do seem just as terrifying.

3. Pluto is a surprisingly clean planet


Instruments on the New Horizons spacecraft included a dust counter, to measure grains of dust as they flew off the planet. During the five days the spacecraft was closest to Pluto, only one grain was picked up by the counter, making Pluto a pretty clean and considerate Kuiper belt resident.

4. Pluto may like to shake things up once in a while

The shoreline of the Sputnik Planum, boasting towering ice mountains (Photo: Nasa)

 Images of the surface of Pluto shows that it has long belts of icy rock that extend violently upwards, sometimes several kilometres high in places, that show evidence of compressional folding. These seem similar to the fault lines seen on Earth, and suggest Pluto has its own tectonic activity and may even experience shifts in the surface when stresses between the belts build up past breaking point.

5. Pluto’s atmosphere was a lot thinner than once thought 

Pluto’s atmosphere in infrared wavelengths (Image: Nasa)

Data from the spacecraft showed that the depth of the atmosphere of the planet was about one hundred times smaller than anticipated, because it was a lot cooler than the researchers first predicted.

Initial calculations failed to take into account the cooling effects hydrogen cyanide and acetylene were also having on the atmosphere, effectively shrinking it in size and causing the atmosphere to cling more closely to the surface of Pluto.

6. Charon, Pluto’s biggest moon, is surprisingly icy, but researchers aren’t sure why


 The team found that the surface of Charon is covered in frozen water, but also had patches of frozen ammonia too, in compositions unlike those found on any other body in the outer solar system.

7. Pluto has its very own halo

The layers of haze in Pluto’s atmosphere (Photo: Nasa)

Photos also show that the planet features its own halo of light, described as hazes, which really took the researchers by surprise. The hazes are distinct bands of blue and white light that extend to altitudes greater than 200 km from the surface of Pluto, and are thought to be caused by a mixture of small and large particles in the atmosphere scattering light, in much the same way as Reyleigh scattering here on Earth makes the sky to appear blue.

However, the methane it is leaking is being cold trapped by nearby Charon, and is thought to be the cause of Charon’s reddish hue around its north pole as it settles into the moon’s lithosphere.

8. Pluto is leaking methane into space, all over poor Charon

Pluto-Charon-v2-10-1-15 cropped
Pluto with Charon in the background, with it’s reddish northern pole (Image: wiki commons)

The upper atmosphere of the planet is also leaking gases at a much slower rate than first thought – again due to how much cooler the atmosphere was compared to the researchers’ initial calculations.

9. Pluto’s neighbours are small, bright, and pretty hyperactive

Pluto and Charon are in the middle, and then in order of distance from Pluto is Styx, Nix, Kerberos and Hydra (Gif: Reddit)

Pluto’s four small moons, Nix, Hydra, Kerberos and Styx, were found to be brighter than expected, suggesting they too have icy surfaces. Resolved measurements of the moons found that the largest had a diameter of only 40 km, with Styx and Kerberos being less than 10 km wide.

They also spin a lot faster than Charon and Pluto, with their rapid spin causing them to stretch out in shape to appear almost oval.

There is still more to come…

The New Horizons spacecraft has only delivered around 40% of the data it has collected from Pluto so far: the rest of the data is yet to be transmitted back to Earth. Keep your eyes peeled for more insights into the weird and wonderful world of Pluto, a truly odd icy ball spinning on the edge of our solar system.

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Philippa Skett

Philippa Skett

Media Officer at Institute of Physics
Philippa was the IOP's media officer
Philippa Skett

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