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Atmosphere of Pluto

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Pluto is a dwarf planet located in the far reaches of our solar system. It is surrounded by a thin layer of gases known as an atmosphere.

PIA20362-Pluto-Atmosphere-Released20160114
PIA20362-Pluto-Atmosphere-Released20160114

This atmosphere is unique because Pluto is the only trans-Neptunian object with a known atmosphere. It plays a vital role in shaping the planet's temperature and appearance. The gases in this layer are mostly vaporized from ices on the surface. Understanding this atmosphere helps scientists learn how small, cold worlds function in deep space.

The atmosphere is composed primarily of nitrogen (N2). There are also smaller amounts of methane (CH4) and carbon monoxide (CO). These gases transition from solid ice to gas through a process called sublimation. Nitrogen is the most volatile component, meaning it turns to gas most easily. Carbon monoxide is the second most volatile, and methane is the third. Methane is particularly important because it acts as a strong heating agent. Conversely, carbon monoxide serves as a cooling agent within the atmospheric structure.

PIA20373-Pluto-Atmosphere-Infrared-20150714
PIA20373-Pluto-Atmosphere-Infrared-20150714

High-energy cosmic radiation triggers complex chemical reactions in the atmosphere. This radiation hits the nitrogen, methane, and carbon monoxide gases. These reactions create heavier, non-volatile compounds like ethane (C2H6), ethylene (C2H4), and acetylene (C2H2). Other complex substances include nitriles and hydrogen cyanide (HCN). These heavier materials eventually precipitate, or fall, back down to the surface. They also form tholins, which give Pluto its distinct brown color.

MVIC sunset scan of Pluto
MVIC sunset scan of Pluto

A striking feature of Pluto is its multi-layered haze. This haze covers the entire planet and reaches altitudes above 200 km. New Horizons observed about 20 distinct layers of this haze. Each layer can be between 1 km and over 10 km thick. The vertical distance between these layers is approximately 10 km. The haze is much denser in the northern regions than near the equator. This haze is blue in color, which suggests very small particles. These particles likely form clusters that are hundreds of nanometers in size.

Near-Surface Haze or Fog on Pluto
Near-Surface Haze or Fog on Pluto

The temperature of Pluto's atmosphere changes significantly with altitude. The surface is very cold, with a mean temperature of about 40 K. However, the temperature rises quickly as you move upward into the stratosphere. This happens because of a methane-generated greenhouse effect. The temperature reaches a maximum of about 70 K at an altitude of 35 km. This peak is known as the stratopause. Above this point, the temperature decreases in the mesosphere. Scientists believe carbon monoxide or hydrogen cyanide might cause this cooling.

PossibleCloudsonPluto
PossibleCloudsonPluto

Scientists have studied Pluto's atmosphere since the 1980s using Earth-based methods. They used spectroscopy and stellar occultations to gather data. An occultation occurs when Pluto passes in front of a star. This allows researchers to see how the atmosphere absorbs or bends light. In 2015, the New Horizons spacecraft provided the first close-up measurements. It measured the surface pressure at approximately 1 Pascal. This is only about 1/100,000 of the atmospheric pressure found on Earth.

PIA19716 Alice Solar Occultation (cropped)
PIA19716 Alice Solar Occultation (cropped)

Pluto's atmosphere experiences strong seasonal changes due to its orbit and axial rotation. As Pluto moves, surface ices migrate through sublimation and condensation. This can cause the thickness of surface ice to change by several meters. These shifts change the brightness and color of the planet. The atmosphere is most similar to the atmosphere of Triton, a moon of Neptune. It also shares some characteristics with the atmosphere of Mars. Studying Pluto provides a window into the complex systems of the outer solar system.

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🖼️ Images & Media (7)
File:PIA20362-Pluto-Atmosphere-Released20160114.jpg
PIA20362-Pluto-Atmosphere-Released20160114.jpg
File:MVIC sunset scan of Pluto.jpg
MVIC sunset scan of Pluto.jpg
File:Near-Surface Haze or Fog on Pluto.jpg
Near-Surface Haze or Fog on Pluto.jpg
File:PIA19716 Alice Solar Occultation (cropped).jpg
PIA19716 Alice Solar Occultation (cropped).jpg
File:PossibleCloudsonPluto.jpg
PossibleCloudsonPluto.jpg
File:PIA20373-Pluto-Atmosphere-Infrared-20150714.jpg
PIA20373-Pluto-Atmosphere-Infrared-20150714.jpg
File:PIA21061-Pluto-DwarfPlanet-XRays-20160914.jpg
PIA21061-Pluto-DwarfPlanet-XRays-20160914.jpg
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