Tuesday, October 5, 2021

Pluto's atmosphere is diminishing. Why is this happening?

 Astronomers took advantage of an occasion when Pluto passed in front of a star on the night of August 15, 2018, to observe how the dwarf planet's atmosphere was behaving.  This method has been used since 1988 to monitor the atmospheric effects there, but something different was found: the density of the atmosphere is decreasing.

 Pluto's observations in its rare opposition may indicate an active surface

 For this observation, a team of astronomers deployed telescopes at various locations in the United States and Mexico, and waited for the moment when the star would disappear behind the object.  Just before concealment, starlight passes through the planet's atmosphere before reaching the lenses of scientific instruments on Earth.  Thus, this light altered by the Plutonian "airs" presents a different profile on the scientists' graphs.

 These graphs serve as evidence to determine the composition of the atmosphere and the quantity of each element in that space, that is, the density.  From 1988 until the unprecedented measurements taken by the New Horizons mission in 2015, astronomers have seen Pluto's atmosphere double in volume every decade, but this time the story was different.

 According to data collected on the star's occlusion, which lasted about two minutes, the general atmospheric abundance is starting to disappear.  This is because it falls back onto the dwarf planet's surface, then freezes.  This was verified through a W-shaped profile in the concealment light, indicating that, in the middle of the process, a "flash" of the eclipsed light ended up "escaping".

 The composition of Pluto's atmosphere is dominated by nitrogen and sustained by the vapor pressure of its surface ices.  This means that small changes in the temperature of the dwarf planet's frozen surface would result in large changes in the density of its atmosphere.  But what caused these changes in temperature?  The answer is simple: the distance from the Sun.

 Pluto takes 248 Earth years to complete a complete revolution around the Sun, in an elliptical trajectory, that is, in an oval shape.  This means that its distance from the Sun varies, with the closest point calculated at about 30 astronomical units from the Sun (1 AU is the distance from Earth to the Sun) and the furthest point at 50 AU.  That is, Pluto can be 50 times farther from the Sun than the average distance between Earth and our star.

 It's been at least 25 years since Pluto has been moving away from the Sun, but only now are the effects of this distance appearing in its atmosphere.  Astronomers attribute this to a heat-conserving effect, just as the sand on a beach is warmer in the late afternoon, even with the sun's weakest, because of the build-up of heat throughout the day.

 The findings will help scientists improve their understanding of the ice sheets on Pluto, in particular //Ă¹the possible compositions that correspond to heat transfer mechanisms.  Ultimately, this will help create more accurate atmospheric models for simulations involving the dwarf planet.

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