An Ancient Solar System...: What in the worlds made Pluto and Charon so complex?

Saturday 18 July 2015

What in the worlds made Pluto and Charon so complex?

Above: An artists impression of Charon, as seen from Pluto.

OK, at this point the New Horizons flyby of Pluto is well over. Data is trickling back to Earth at a steady rate, and this will be the norm now for several months at least. So I promise that this will be the last post where I geek out over the latest results to trek across deep space and arrive home (cough, cough)... but.....

Yesterday (Friday 17th July) NASA held a press conference on... all kinds of Pluto-y things: Firstly, the Pluto 'heart' where New Horizons has confirmed presence of carbon monoxide ice covering it, the only such high concentration on the planet. Carbon Monoxide is actually pretty rare across the rest of Pluto - and one part of the heart has so much the spectral signature is visible from Earth. Why it should have so much really isn't clear, but it's possible there's a CO source in that region - which would indicate some kind of internal activity breaking out to the surface...

Above: The area of the 'Pluto heart' with the intense carbon monoxide ice signature. That's a lot of CO in one spot.... Courtesy of NASA

Another huge plain, Tombaugh Regio, is broken into massive polygon shaped plates. Along the edges of the polygons are some sort of cracks.... as well as weird mounds that almost seem to be growing out of them, and an unidentified dark material. Some of the cracks have ridges running along their centres:

Above: Some of the cacks with central ridges, indicating rowth, perhaps.

Above: Tombaugh Regio. The black things that look like they're growing out of the cracks are hills made of an unknown black material. Courtesy of NASA.

Origin, and precise shape of the strange hills is unknown. There're some sign that they rise above the surrounding plains, and the geophysics have two theories; They could be erupted from below, like volcanoes or could be harder material left behind as erosion from above lowers the height of the plain. They are - very unofficially - slightly leaning towards the eruption idea, but only very slightly:

“This terrain is not easy to explain,” said Jeff Moore, leader of the New Horizons Geology, Geophysics and Imaging Team. “The discovery of vast, crater less, very young plains on Pluto exceeds all pre-flyby expectations.” One odd idea being bandied about by astrogeologists is that some of these features might be liquid carved, like the liquid methane rivers on Titan, This is defiantly an odds against idea, but there are some liquids that might exist on Pluto.

Other news comes from the probe's analysis of Pluto's atmosphere, which is made of nitrogen, and is being stripped away by the solar wind at 500 tons per second. That rate of loss compares unfavourably even to Mars ( which looses its air at at 1 ton per second). Over the lifetime of Pluto that's equivalent to a loss of several thousand feet of nitrogen ice - assuming the atmosphere is being replenished by evaporating ice. The atmosphere s around 1000km deep - almost as deep as the dwarf planet is wide - and the winds in its lower levels strong enough to move particles and cause erosion, which means that Pluto's surface will be eroded and shaped by them.

Some evidence of this has already been picked up as streaks on dark material, apparently blown by the wind, seen on surface. The origin of the dark stuff might be due to geyser like eruptions, or it might be entirely due to wind eroding deposits of dark material - there's no evidence of eruptions but the team will be looking.