A radio image of Saturn shows traces of past storms. The broad, bright band near the top of the image is the aftermath of a 2010 storm
R. J. Sault and I. de Pater
Saturn experiences massive storms every 10 to 20 Earth years, often spanning kilometers and leaving behind distinct white marks in its atmosphere. These storms have caught the attention of scientists who have now discovered that the aftermath of these tempests can last for hundreds of years.
Researchers used the Karl G. Jansky Very Large Array in New Mexico to map ammonia distribution on Saturn. Since ammonia behaves in a similar manner to water in Earth’s atmosphere, Cheng Li and his team at the University of Michigan wanted to investigate how it behaved following Saturn’s most recent storm in 2010. To their surprise, they found evidence that the planet’s atmosphere was still influenced by storms that occurred as early as 1876, if not earlier.
“We know that these storms are big, but based on our daily experience of weather we’ve never considered the possibility that these storms can leave such a long remnant after hundreds of years,” says Li. “On Earth, weather comes and goes, but on Saturn it sticks around.”
The anomalies observed were regions in the atmosphere where ammonia levels were lower at higher altitudes but higher at lower altitudes. These areas likely indicate that ammonia from the upper atmosphere condensed and fell as hail-like “mushballs” before evaporating and lingering as vapor in the lower atmosphere.
“On Earth, if you have a heavy rain you accumulate water on the ground in puddles,” explains Li. “But on giant planets there’s no surface, so where could that rain go? It just evaporates.”
The researchers identified patches of anomalies corresponding to all six giant storms observed on Saturn since 1876, and even one additional patch believed to be from a storm that occurred decades earlier. The movement of these anomalies in the aftermath of the storms could provide insights into the winds and currents within Saturn.
Interestingly, these observations of Saturn’s weather stand in contrast to similar studies of storms on Jupiter, potentially shedding light on the inner workings of gas giants as a whole. “They have similar compositions, they have similar gravity, but why is the weather so different? It’s these contrasts that can help us understand giant planets,” says Li.
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