How cold is pluto
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Understanding Pluto's Cold Temperature
Pluto's Atmosphere: Haze and Temperature Regulation
Pluto's atmosphere is notably cold and hazy, with recent observations revealing it to be much colder than theoretical predictions. This discrepancy suggests an unknown cooling mechanism at play. Research indicates that atmospheric haze particles, rather than gases, are primarily responsible for regulating Pluto's temperature. These haze particles have significantly higher solar heating and thermal cooling rates compared to gas molecules, thus dominating the atmospheric radiative balance up to an altitude of 700 kilometers. Above this altitude, heat conduction maintains an isothermal atmosphere.
Seasonal and Long-Term Surface Temperature Variations
Pluto experiences dynamic surface temperature variations driven by its seasonal and long-term orbital changes. The planet's 248-year orbit, along with its obliquity precession and the regression of its orbital longitude of perihelion, creates periods of "Extreme Seasons." During these times, one pole undergoes a short, relatively warm summer and a long winter, while the other experiences a longer, less intense summer and a short winter. These variations, coupled with Pluto's albedo contrasts, result in significant temperature effects. For instance, the bright region known as Sputnik Planitia acts as a persistent cold trap, maintaining its low temperature over million-year timescales.
Comparative Analysis with Triton
Pluto's atmosphere shares similarities with Neptune's largest moon, Triton, in terms of cold surface temperatures and atmospheric pressures. However, the methane (CH4) mixing ratio profiles play a crucial role in differentiating their atmospheres. On Pluto, the surface CH4 mole fraction is high enough to ensure it is well-mixed in the lower atmosphere, whereas on Triton, the lower CH4 mole fraction leads to its photochemical destruction in the lower atmosphere. This results in nitrogen (N2) remaining the major species in Triton's atmosphere, even at higher altitudes.
Insights from New Horizons
The New Horizons mission provided a detailed snapshot of Pluto's atmosphere, revealing it to be colder and more compact than expected. The atmosphere is primarily composed of nitrogen and methane, with extensive layers of haze. The cold upper atmosphere implies much lower escape rates of volatiles than previously predicted, significantly impacting the volatile recycling and long-term evolution of Pluto's atmosphere.
Climate Modeling and Predictions
Recent climate models, incorporating new observational data, suggest that Pluto's atmosphere will not collapse before the arrival of New Horizons, although atmospheric pressure will decrease as nitrogen condenses on the south polar cap. These models predict a range of surface pressures, with the best match indicating an atmospheric pressure of 2.4 Pa in 2015. Additionally, a new 3D Global Climate Model (GCM) simulates Pluto's climate and ice cycles, showing that the planet's climate is highly sensitive to model parameters and initial states. The GCM predicts a cold atmospheric layer above Sputnik Planitia, resulting from the combined effects of topographic depression and nitrogen sublimation.
Conclusion
Pluto's cold temperature is a result of complex interactions between its atmospheric haze, seasonal and long-term orbital variations, and unique atmospheric composition. The insights gained from the New Horizons mission and advanced climate models have significantly enhanced our understanding of Pluto's climate, revealing the intricate mechanisms that regulate its temperature.
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