Neptune temperature
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Neptune's Temperature: An Overview
Upper Atmosphere Temperature of Neptune
The temperature in Neptune's upper atmosphere has been a subject of extensive study. Observations from the occultation of the sun by Neptune suggest that the temperature in the upper levels of the atmosphere, which is primarily composed of atomic and molecular hydrogen, is approximately 750 ± 150 kelvins 1. This high temperature is consistent with the emissions observed in the ultraviolet spectrum, which are dominated by hydrogen Lyman α emissions 1.
Stratospheric Temperature and Hydrocarbon Abundances
Neptune's stratosphere exhibits a significantly lower temperature compared to its upper atmosphere. Infrared observations have determined that the stratospheric temperature is around 168 K at pressures near 1-10 μbar, with an uncertainty of ±10 K 2. This temperature profile is consistent with the detected emissions of various hydrocarbons such as methane (CH4), acetylene (C2H2), and ethane (C2H6) 2. The abundances of these hydrocarbons are crucial for understanding the thermal dynamics and chemical composition of Neptune's atmosphere.
Tropopause and Lower Atmosphere
The tropopause, a boundary layer in Neptune's atmosphere, is located approximately 40 km above the 1-bar pressure level, where the temperature is about 52 ± 2 K 5. This region marks a significant drop in temperature and is characterized by a mixture of hydrogen and helium gases 5. The effective temperature of Neptune, which is a measure of the planet's overall thermal emission, has been determined to be around 55.5 ± 2.3 K, indicating that Neptune radiates twice as much energy as it receives from the Sun 8.
Seasonal and Latitudinal Variations
Ground-based observations from 2003 to 2007 have provided insights into the seasonal and latitudinal temperature variations on Neptune. These studies reveal that the stratospheric temperatures tend towards a quasi-isothermal structure, ranging between 158-164 K above the 0.1-mbar level 7. Despite different observing conditions, these temperatures have shown remarkable consistency, suggesting minimal temporal variability. However, significant temperature enhancements have been observed at high southern latitudes, indicating a polar warming of 7-8 K above the tropopause 7.
Exospheric Temperature Predictions
The exospheric temperature of Neptune, which is the temperature at the outermost layer of the atmosphere, has been predicted to be around 200 K. This prediction is based on the assumption that Neptune's magnetosphere lacks the significant tilt and offset observed in Uranus, leading to lower auroral energy inputs and consequently a cooler exosphere 6.
Conclusion
Neptune's atmospheric temperatures vary significantly across different layers, from the upper atmosphere to the stratosphere and tropopause. The upper atmosphere is notably hot, while the stratosphere and lower layers are much cooler. Seasonal and latitudinal variations also play a crucial role in the thermal dynamics of Neptune's atmosphere. These findings provide a comprehensive understanding of the complex thermal structure of Neptune, contributing to our broader knowledge of planetary atmospheres in our solar system.
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