Pluto's atmosphere observed by NASA's mission in 2015. Credit: NASA/JHU-APL/SwRI

Pluto’s Atmosphere is Slowly Vanishing Into Outer Space

Pluto's period of rotation around the Sun is 248 years. Its atmosphere will form once again when the dwarf planet comes closer to our star.

Pluto’s atmosphere is very thin, and its main component is nitrogen with insignificant admixtures of methane and carbon monoxide. The further the dwarf planet moves away from the Sun, the lower its surface temperature becomes. Nitrogen freezes into ice and causes the atmosphere to disappear gradually.


What do we know about Pluto’s atmosphere and why does it change?

New Horizons

In July 2015, Pluto was approached by the New Horizons probe, which explored the dwarf planet up close for the first time. In particular, the data collected showed that Pluto’s atmosphere is composed of several layers and contains volatiles such as nitrogen and methane, which form a bluish haze visible in photographs.

What else did the spacecraft reveal?

In addition, Pluto’s atmosphere turned out to be much colder than the theoretical models existing at that time assumed. This means that there is some unaccounted-for mechanism for cooling the atmosphere. Another thing – it turned out that its atmosphere extends more than 1600 kilometers from the surface of the planetoid. Its upper layers consist mainly of molecular nitrogen, while the near-surface layers contain a certain amount of hydrocarbons.

The haze layer of Pluto's atmosphere in an image taken by the New Horizons spacecraft. Credit: NASA/JHUAPL/SwRI
The haze layer of Pluto’s atmosphere in an image taken by the New Horizons spacecraft. Credit: NASA/JHUAPL/SwRI

How did astronomers study the atmosphere of Pluto without a dedicated mission?

Since we do not have spacecraft orbiting the planet and data is scarce, there are other methods to find and observe the atmospheres of distant objects. For this, they use the so-called covering method: when one cosmic body, from the point of view of the observer, overlaps another cosmic body. In Pluto’s case, it covered one of the distant stars in 2018, and its glow was used by astronomers as a kind of illumination for their telescopes.

Rotation around the Sun

Pluto’s period of rotation around the Sun is 248 years. When a planet is at perihelion (the closest point to a star), its frozen surface begins to warm up. The ice melts, turning into gas, which saturates Pluto’s atmosphere.

A virtually unprocessed (left) and processed (right) photograph of the glow of Pluto's atmosphere Credit NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
A virtually unprocessed (left) and processed (right) photograph of the glow of Pluto’s atmosphere Credit NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute

Thermal inertia

However, why did scientists notice this only now, when the dwarf planet has already considerably moved away from the star? It’s all about the residual heat, or, as astronomers call it, the thermal inertia of the planet.

Explanation

It can be compared to the sand on the beach. It is cool in the morning but begins to warm up towards the middle of the day. In the evening, when the sun is almost hidden, the sand is especially hot. Much the same is happening on Pluto.

Pluto is becoming colder

As it moves away from the star in its orbit, Pluto slowly cools. The residual heat is increasingly leaving space and the atmosphere of the dwarf planet freezes and disappears. In a way, it seems to evaporate.

Pluto’s atmosphere will form again

However, after a couple of centuries, Pluto will approach the Sun once again and ice will once again begin to evaporate, enveloping the planet in a light ghostly haze.


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Sources:

Gohd, C. (2021, October 8). Pluto’s atmosphere is starting to disappear, scientists find. Space.com.
Nield, D. (n.d.). Pluto’s atmosphere is slowly vanishing, scientists discover. ScienceAlert.
Phys.org. (2021, October 4). Scientists confirm decrease in pluto’s atmospheric density.
Southwest Research Institute. (2021, October 4). SWRI scientists confirm decrease in pluto’s atmospheric density.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. My experience as a freelance writer began in 2018 but I have been part of the Curiosmos family since mid-2020. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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