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Whenever it passes in front of a star, Pluto provides precious information about its atmosphere, precious because occultations by Pluto are rare. The survey achieved by researchers from Paris Observatory over several decades of observations appears in the journal Astronomy and Astrophysics of May 10, 2019. Interpreted in the light of data collected in 2015 by the probe New Horizons, it allows them to refine physical parameters that are essential for a better understanding of Pluto's climate and to predicting future stellar occultations by the dwarf planet.
Like Earth, Pluto's atmosphere is essentially composed of nitrogen but the comparison stops there.
Beyond - Neptune - Pluto - Years - Revolution
Beyond Neptune, Pluto takes 248 years to make a complete revolution around the sun. During a Plutonian year, its distance to the sun varies greatly from 30 to 50 au, leading to extreme seasonal cycles.
With extremely low surface temperatures, less than -230 ° C (40 ° K), there is a solid-gas equilibrium, where a tenuous atmosphere of essentially nitrogen coexists with surface ice deposits. Today, the nitrogen vapour is estimated to be stabilised at a pressure around 1.3 pascal (whereas the pressure is about 100 000 Pa on our planet).
Obliquity - Angle - Axis - Plane - Degrees
Because of its obliquity (the angle formed between the polar axis and the orbital plane) at 120 degrees, Pluto's poles successively face a permanent day for several decades, then a permanent night. This leads to a complex cycle of redistribution of its volatile species such as nitrogen, methane and carbon monoxide. Thus Pluto had its equinox in 1988, before moving to perihelion (at 30 au) in 1989. Since then, the dwarf planet has continually moved away from the sun to reach 32 ua in 2016, which represents a loss of 25 percent of his average insolation.
Atmospheric pressure at the surface of Pluto as a function of time, from 1988 to 2238. Credit:...
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