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Research shows Pluto’s atmosphere does not collapse throughout its orbital year

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Posted September 5, 2013

The amount of sunlight reaching the surface of Pluto constantly changes over the entire orbital year of this dwarf planet due to eccentricity and obliquity of its orbit. This change leads to the variations of planetary surface heating. In theory, the additional amount of heat should transform the local frozen methane (CH4) and nitrogen (N2) into gaseous state. And, according to some hypotheses, such colossal release of gas should dramatically increase the atmospheric pressure during each orbital year of the planet, which lasts almost 248 Earth years.

This idea could seem completely logical at first, especially considering the fact that the amount of sunlight received by the dwarf planet changes almost three times, when comparing Pluto’s farthest and nearest orbital positions (the aphelion and perihelion).

So do such Pluto’s atmosphere collapses really take place? No, according to an international research team, which includes scientists from the USA, Brazil, Belgium, Spain, Chile and the UK. The scientists presented their research in a paper published at arXiv.org.

The team created a model of energy balance between Pluto’s surface layer and the surrounding atmosphere. The data required for this model has been obtained during Pluto’s occultation on May 4, 2013. According to the authors, this measurement method provides the most sensitive and precise data indicating seasonal changes in planet’s atmospheric pressure.

The measurements were performed simultaneously at five observatories in the South America: Cerro Burek (Argentina), LCOGT at Cerro Tololo (Chile), Pico dos Dias (Brazil), La Silla Observatory (Chile) and San Pedro de Atacama (Chile). Then a geometrical calculation of the occultation light curve was performed to determine a precise location of the Sun relative to Pluto. Finally, the scientists used the Pluto’s atmosphere model developed by another team of researchers back in 1992 during another occultation and applied the obtained light curve measurement data to it.

Results of the analysis were compared with similar observations from 1988 and 2010. Contrarily to the previous calculations, scientists were able to prove that hypothesis related to the periodic collapses of Pluto’s atmosphere wasn’t  true, since only relatively slight pressure variations were determined over the course of several consecutive observations.

The authors suggest that the high thermal inertia of the planetary surface substrate may be the reason for the absence of larger atmospheric changes. The heat accumulated at the sunlit side of the dwarf planet is exchanged with it’s colder dark hemisphere via gaseous ice sublimation and condensation mechanisms; this balance keeps the surface ice at the similar temperature over the course of the orbital year.

Also, this model provides more arguments for the similarity between Pluto and Triton: these bodies are similar in size, density and surface composition, and now it appears that they share similar surface material thermal inertia properties.

The team notes, that their research could be tested additionally in the future, as, according to the current models, Pluto’s surface pressure should reach the maximum somewhere between 2020 and 2040.

By Alius Noreika, source: Technology.org

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