Temperature of planets
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Temperature of Planets: An Overview
Factors Influencing Planetary Temperatures
Solar Luminosity and Distance from the Sun
The surface temperatures of planets in our solar system are primarily influenced by the luminosity of the Sun and the distance of the planet from the Sun. These factors determine the amount of solar energy a planet receives, which is crucial for its surface temperature2.
Albedo and Internal Heat
Another significant factor is the planetary bolometric albedo, which is the fraction of solar energy reflected by the planet. A higher albedo means more reflection and less absorption, leading to cooler temperatures. Additionally, the heat welling up from the planet's interior also contributes to its surface temperature2.
Temperature Variations in Exoplanets
CoRoT-9b: A Temperate Giant
CoRoT-9b is a transiting giant exoplanet with a photospheric temperature estimated to be between 250 K and 430 K. This range is considered temperate compared to other known transiting planets. The planet orbits its star with a period of 95.274 days and has a low eccentricity, which contributes to its relatively stable temperature1.
HD 149026b: The Hottest Known Planet
HD 149026b is noted for its extreme temperatures, with a brightness temperature of approximately 2,300 K at 8 µm. This high temperature is attributed to the planet's low albedo and the efficient re-emission of received stellar radiation. The planet's temperature is significantly higher than the predicted temperature for a uniform, spherical blackbody emission, indicating unique atmospheric properties3.
Modeling Planetary Temperatures
Earth-like Planets
For Earth-like planets, surface temperature models (ESTM) are used to study habitability. These models consider factors such as radiative-convective atmospheric calculations, meridional transport, and surface and cloud properties. The ESTM can predict temperature variations based on different planetary parameters, such as rotation rate, insolation, and surface pressure4.
Runaway Greenhouse Effect
The maximal runaway temperature of Earth-like planets is influenced by the greenhouse effect, which can saturate and limit the maximum temperature. For instance, a hypothetical planet similar to Venus could have a maximum surface temperature of 1200-1300 K, depending on its atmospheric composition and distance from its star5.
Temperature Measurements of Giant Planets
Far-Infrared and Submillimeter Observations
The brightness temperatures of giant planets like Jupiter, Saturn, Uranus, and Neptune have been measured in the far-infrared and submillimeter ranges. These measurements provide insights into the planets' bolometric output and atmospheric structure. For example, Jupiter's effective temperature is around 126.8 K, while Saturn's is approximately 93.4 K7.
Equilibrium and Surface Temperatures
Impact of Orbital Eccentricity
The equilibrium temperature of planets in elliptical orbits tends to decrease with increasing eccentricity. This is contrary to the assumption that higher eccentricity would lead to higher temperatures. The actual equilibrium and surface temperatures also depend on variations in albedo and greenhouse effects, which are crucial for understanding planetary climates and habitability8.
Albedo and Habitability
The potential habitability of exoplanets is often assessed by their equilibrium temperature, which is influenced by their albedo. For habitable planets, the Bond albedo can vary significantly, affecting their surface temperatures. General circulation models help predict these variations and provide estimates of potential habitability based on known stellar parameters9.
Conclusion
The temperature of planets is a complex interplay of various factors, including solar luminosity, distance from the Sun, albedo, and internal heat. For exoplanets, additional factors such as orbital eccentricity and atmospheric properties play significant roles. Understanding these factors is crucial for assessing planetary climates and the potential habitability of exoplanets.
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Most relevant research papers on this topic
A transiting giant planet with a temperature between 250 K and 430 K
CoRoT-9b, the largest transiting planet, has a 'temperate' photospheric temperature between 250 and 430 K and an interior composition consistent with Jupiter and Saturn.
Highly CitedThe hottest planet
The smallest known transiting planet, HD 149026b, has a brightness temperature of 2,300 200 K at 8 m, making it the hottest known extrasolar planet.
Highly Cited