Even though the gas giants of our solar system Neptune, Uranus, Saturn, and Jupiter are far away from Sun, their atmosphere’s upper layers are hot just like our Earth’s. Their heat source has remained a mystery but a new study claims to have found a viable explanation for it.
The research published in the journal Nature Astronomy is the most complete mapping yet of both temperature and density of a gas giant’s upper atmosphere, which is based on the data from the Cassini spacecraft which observed Saturn for more than 13 years before exhausting its fuel supply.
Electric currents make upper atmosphere hot
As per the study, the auroras at the Saturn’s north and south poles could be making it very hot, as well as possibly the other gas giants like Jupiter, Neptune, and Uranus. The electric currents triggered by interactions between solar winds and charged particles from Saturn’s moons, spark the auroras and heat the upper atmosphere— just like the case with Earth’s northern lights, NASA’s Jet Propulsion Laboratory (JPL) said in a press release.
Building a complete picture of how heat circulates in the atmosphere, enabled scientists to better understand how auroral electric currents heat the upper layers of Saturn’s atmosphere and drive winds. According to the study, the global wind system can distribute the energy deposited near the poles toward the equatorial regions, heating them to twice the temperatures expected from the Sun’s heating alone.
Cassini’s role in the finding
The study author Tommi Koskinen who is also a member of Cassini’s Ultraviolet Imaging Spectrograph (UVIS) team said that the results are an important part of Cassini’s legacy and help address the question of why the uppermost part of the atmosphere is so hot while the rest of the atmosphere is cold due to the large distance from the Sun.
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The density of the atmosphere of a planet decreases with altitude and the rate at which it decreases depends on the temperature. Measuring the density of Saturn’s atmosphere using data from the Cassini mission gave the researchers information they needed to find the temperatures. They found that temperatures peak near the auroras, indicating that the electric currents near the poles heat the upper atmosphere.
As per the study, understanding Saturn’s upper atmosphere, where planet meets space, is the key to understanding space weather and its impact on other planets in our solar system and exoplanets around other stars.