The fascinating icy surface of Pluto is covered in red spots of tholins, but new experiments have shown that the exact nature of these formations remains unclear. Scientists were unable to reproduce the observational data obtained by the New Horizons probe in 2015 when they experimented with synthesized tholins.
Everything you need to know about the massive red spots on Pluto
1. In 2015, when the far space probe New Horizons first visited the Pluto system, it noticed extensive patches/spots of red dust on the light surface of the dwarf planet and its moon Charon.
2. Spectral characteristics showed that they consist mainly of tholins – a complex mixture of polymers that arise from simple organic compounds under the influence of solar ultraviolet radiation.
3. Tholins are fairly common in the outer solar system. Having formed in the upper layers of Pluto’s rarefied atmosphere, they can fall to the surface as “rusty snow”.
4. However, new experiments by Marie Fayolle and her colleagues at the Delft Institute of Technology in the Netherlands show that the question of the nature of the red spots on Pluto is far from closed.
5. Scientists synthesized a mixture of tholins in the laboratory, which formed micrometer-sized spherical dust fragments. Then they obtained a reflection spectrum of these compounds under conditions as close as possible to those existing on the dwarf planet.
6. The experiments were carried out in an atmosphere of nitrogen, carbon dioxide, and methane, bombarded with high-energy particles that simulate cosmic radiation.
7. In the infrared, the spectrum did not quite coincide with the data that New Horizons received while flying over Pluto, some absorption lines in it turned out to be “superfluous”. The authors put forward several hypotheses to explain these deviations.
8. Firstly, after long-term treatment with space particles and thicknesses can partially degrade, slightly changing the color and spectrum. Or it may be due to the porosity of the surface of Pluto in the areas of red tholine spots.
9. Possibly, the pores are formed due to the fact that Pluto is not massive enough and the precipitated substances accumulate loose “snow” on it. However, the same pores can appear during sublimation – evaporation without a transition to the liquid phase – local ice.
10. The area of Cthulhu Macula on Pluto, which is almost completely covered by red tholine spots, is located at the equator, and there is practically no nitrogen or methane ice there. However, methane can be seasonal and appear during the long local winter and disappear by summer, leaving a porous surface dotted with a layer of tholins.
Unfortunately, there are no planned missions towards Pluto currently. There were talks of two follow-ups for New Horizons in the past but nothing has been announced. Still, I believe there is more to learn from the unstudied data from the last flyby and astronomers will be well occupied for the years to come. The whole point of understanding Pluto’s red spots is to learn more about the planet’s interaction with its atmosphere.
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• Crane, L. (2021, June 21). Pluto is covered in huge red patches and we don’t know what they are. New Scientist.
• Fayolle, M., Quirico, E., Schmitt, B., Jovanovic, L., Gautier, T., Carrasco, N., Grundy, W., Vuitton, V., Poch, O., Protopapa, S., Young, L., Cruikshank, D., Ore, C. D., Bertrand, T., & Stern, A. (2021, June 2). Testing tholins as analogues of the dark reddish material covering Pluto’s Cthulhu region. Icarus.
• Starr, M. (n.d.). The Red Plains of Pluto’s Cthulhu Macula May Not Be What We Thought. ScienceAlert.
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