Uranus, the planet that orbits side, has always been the weirdo of our solar system. Since NASA’s Voyager 2 probe survived it in 1986, astronomers have dealt with a disconcerting mystery: unlike their gaseous Jupiter, Saturn and Neptune cousins, Uranus seemed not to have an important internal heat source. It was, in appearance, an inert and energetically dead world. But that idea has just jumped through the air.
A little context. In January 1986, the Voyager 2 probe became the first and only ship to visit Uranus, giving us the most iconic images of the planet and the data that laid the foundations of everything we know about him. One of the most important was its energy balance, the heat it emits with respect to the sun.
The giant planets have an immense mass, so they retain a considerable amount of the heat of their formation and release it over billions of years. This internal heat flow is evident in Jupiter, Saturn and Neptune. However, the Iris instrument of Voyager 2 told a very different story about Uranus.
According to a 1990 study, the planet issued an almost identical amount of energy to what it received from the sun: the internal heat flow was statistically indistinguishable from zero. Uranus thus became the anomaly of the Solar System: an ice cream giant that, for some reason, had cooled much faster or formed in a completely different way from the other planets.
I wasn’t dead. Nor of Parranda. A new study led by researchers at the University of Houston has finally resolved the mystery. After analyzing decades of data, scientists have shown that Uranus does emit more heat than he receives from the Sun. It is not the inert planet we thought, but a dynamic world with an internal engine that, although modest, is very present in the energy balance.
The error was not in the measurements of Voyager 2, but in the interpretation of a single snapshot over time. This is where the new study led by Xinyue Wang and Liming Li, from the University of Houston. Instead of based only on the overflow of 1986, his team compiled and analyzed data from a much longer period (from 1946 to 2030), covering almost a complete orbit of Uranus, which lasts 84 terrestrial years.
Uranus is a planet of extremes. Its rotation axis is inclined 97.7 degrees, so it basically rolls on its orbit. Combined with a remarkably long orbit, it causes extreme stations that last about 21 years each, with a hemisphere bathed by continuous sunlight while the other remains in an icy darkness.
The researchers discovered that this seasonal cycle is the key to everything. The solar energy that absorbs the planet is not constant, but varies significantly throughout its year. The 1986 analyzes, made near the winter solstice of the northern hemisphere, did not capture the complete image. By averaging the energy balance throughout the orbit, the results are unequivocal: Uranus consistently emits 12.5% more energy than he receives from the sun.
Not so weird bug. Uranus now fits much better in the formation models of giant planets. It has an internal engine, although it is weaker than that of its neighbors, which suggests that its evolution was more similar to that of the rest of what was thought. This finding not only changes our understanding about how giant planets are formed and evolved, but comes at the right time, when both NASA and China prepare missions to visit it.
If the question is why Voyager 2 obtained such a misleading image of the planet, the answer is simply bad luck. In the days prior to the 1986 overflight, the Sun bombed Uranus with an unusually powerful geomagnetic storm. This phenomenon compressed the magnetosphere of the planet, which caused the ship to capture data in a day of extreme conditions.
Imagen | Nasa/Erich Karkoschka
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