They determine the age and origin of Jupiter’s Great Red Spot.

Researchers from the University of the Basque Country, the Polytechnic University of Catalonia – BarcelonaTech (UPC) and the National Supercomputing Center (CNS-BSC) published their observations and numerical models in the journal Geophysical Research Letters of the American Geophysical Union. .

Researchers from the University of the Basque Country, the Polytechnic University of Catalonia – BarcelonaTech (UPC) and the Barcelona Supercomputing Center – Centro Nacional de Supercomputación (CNS-BSC) analyzed historical observations dating back to the 17th century and developed numerical models to explain the durability and nature of this impressive meteorological phenomenon in the atmosphere of a gas giant planet. The work was published in the American Geophysical Union’s journal Geophysical Research Letters.

Jupiter’s Great Red Spot (known as the GRS) is probably the most famous atmospheric structure, a popular symbol among solar system objects. Its large size (currently equal to the diameter of Earth) and the contrast of its reddish color with the planet’s pale clouds make it an easily visible object even in small telescopes. Jupiter’s red spot is a huge anticyclonic vortex, along the periphery of which winds circulate at a speed of 450 km/h. This is the largest and longest-lived vortex of all existing in the atmospheres of the planets of the solar system, but its age is the subject of debate, and the mechanism that gave rise to its formation remains hidden.

Speculation about the origin of the GRS dates back to the first telescopic observations by astronomer Giovanni Domenico Cassini, who in 1665 discovered a dark oval at the same latitude as the GRS and named it the “Permanent Spot” (PS). since it was observed by him and other astronomers until 1713. Subsequently, its trace was lost for 118 years and only in 1831 and in subsequent years S. Schwabe again observed a clear structure, approximately oval in shape and at the same latitude as GRS, which can be considered the first observation of the current GRS, and possibly the nascent GRS. Since then, the GRS has been regularly observed by telescopes and various space missions that have visited the planet, to this day.

In the study, the authors analyzed, on the one hand, the evolution of dimensions over time, its structure and movements of both meteorological formations – the old PS and the GDS; To do this, they turned to historical sources dating back to the mid-17th century, shortly after the invention of the telescope. “From the size and motion measurements, we conclude that it is highly unlikely that the current GRS was the PS observed by GD Cassini. PS probably disappeared somewhere between the mid-18th and 19th centuries, in which case we can say that the Red Spot has, at least for now, a lifespan of more than 190 years,” explains Agustin Sánchez Lavega, professor of physics at UPV. /EHU, who led this study. The Red Spot, which measured 39,000 km along its longest axis in 1879, narrows as it rounds until it currently measures approximately 14,000 km.

On the other hand, since the 1970s, various space missions have closely studied this meteorological phenomenon. Recently, “various instruments on board the Juno mission in orbit around Jupiter showed that the GRS is shallow and thin compared to its horizontal size, as it extends vertically over about 500 km,” explains Sánchez Lavega.

To find out how this huge vortex could have formed, the UPV/EHU and UPC teams carried out numerical simulations on Spanish supercomputers such as the MareNostrum IV BSC integrated into the Spanish Supercomputer Network (RES), using two types of complementary models for the behavior of thin vortices in Jupiter’s atmosphere. The giant planet is dominated by intense wind currents flowing along parallels alternating their direction with latitude. North of the GRS, winds blow in a westerly direction at a speed of 180 km/h, and in the south – in the opposite direction, in an easterly direction, at a speed of 150 km/h. This creates a huge shift in wind speed from north to south, which is a major factor in the growth of the vortex within it.

In the study, they examined various mechanisms to explain the origin of the GRS, including the eruption of a giant superstorm similar to those very rarely observed on Saturn’s twin planet, or the merger of many smaller vortices resulting from wind shear. The results show that although an anticyclone is formed in both cases, it differs in shape and dynamic properties from the modern GRS. “We also think that if one of these unusual events had occurred, astronomers at the time would certainly have noticed it or its effects in the atmosphere,” says Sánchez Lavega.

In a third set of numerical experiments, the research team examined the generation of GRS due to known wind instability, which the researchers believe is capable of generating an elongated cell that surrounds and confines them. Such a cell could represent a proto-GRS, a nascent Red Spot whose subsequent compression would result in the compact and rapidly rotating GRS observed in the late 19th century. The formation of large elongated cells has already been observed during the emergence of other important vortices on Jupiter. “In our simulations, thanks to the use of supercomputers, we found that elongated cells are stable when they rotate around their periphery at the speed of Jupiter’s winds, as would be expected when they form as a result of such instability,” states Enrique García. -Melendo, Researcher, Department of Physics, SKP. Using two different types of numerical models, one on the UPV/EHU and the other on the UPC, the researchers concluded that if the rotation speed of the proto-GRS is lower than the surrounding winds, it fragments, making it impossible for a stable vortex to form. And if it is very high, then its properties differ from the properties of the current gas distribution system.

Future studies will aim to attempt to reproduce the contraction of GRS over time to understand in more detail the physical mechanisms underlying its maintenance over time. At the same time, they will try to predict whether the GRS will decay and disappear when it reaches its size limit, as Cassini’s PS may have done, or whether it will stabilize at a size limit where it can survive for many more years. .