Astronomers believe they have discovered how and when Jupiter's red spot formed

Universe Jupiter It is particularly famous for the so-called Great Red Spot, a vortex in the gas giant's atmosphere that has been around since at least 1831. But how it was formed and how old it is is still a matter of debate. Astronomers of the seventeenth century, incl Giovanni CassiniThey also reported a similar place in their observations of Jupiter that they called the “permanent spot.” This prompted scientists to wonder whether the spot observed by Cassini was the same spot we see today. We now have an answer to this question: the spots are not the same, according to A New paper Published in the journal Geophysical Research Letters.

“From measurements of sizes and motions, we conclude that the current Great Red Spot is unlikely to be the ‘permanent spot’ observed by Cassini.” said co-author Agustín Sanchez LaVega University of the Basque Country in Bilbao, Spain. “It is possible that the 'permanent spot' disappeared sometime between the mid-18th and 19th centuries, in which case we can now say that the longevity of the red spot exceeds 190 years.”

Jupiter was known to Babylonian astronomers in the 7th and 8th centuries BC, as well as to ancient Chinese astronomers; The latter's observations would lead to the birth of the Chinese zodiac in the 4th century BC, with a 12-year cycle based on the gas giant's orbit around the sun. In 1610, with the help of the advent of telescopes, Galileo Galilei observed the four largest moons of Jupiter, strengthening the Copernican model of heliocentrism in the solar system.

Robert Hooke may have observed the Permanent Spot as early as 1664, and Cassini followed suit a year later with several more observations until 1708. It then disappeared from the astronomical record. A pharmacist named Heinrich Schwabe made the first known drawing of the red spot in 1831, and by 1878 it was prominent again in observations of Jupiter, then faded away again in 1883 and at the beginning of the 20th century.

Maybe the place is not the same.

But was this the same permanent spot observed by Cassini? Sánchez La Vega and his colleagues set out to answer this question, by searching historical sources – including Cassini's observations and drawings from the 17th century – and more recent astronomical observations and measuring the results. They have made year-by-year measurement of the volumes, ellipticity, area and motions of both the permanent macula and the Great Red Spot from the earliest observations recorded in the 21st century.

The team also performed several numerical computer simulations to test different models of vortex behavior in Jupiter's atmosphere that likely underlie the Great Red Spot. It's basically a huge, persistent anticyclonic storm. In one model the authors tested, the spot forms in the aftermath of a massive superstorm. Alternatively, several smaller vortices generated by wind shear may have merged, or there may have been an instability in the planet's wind currents that gave rise to an elongated, spot-shaped air cell.

Sanchez-Lavega et al. He concluded that the current Red Spot may not be the same as the one observed by Cassini and others in the 17th century. They argue that the permanent spot faded away by the beginning of the 18th century, and a new spot formed in the 19th century – the one we observe today, making it more than 190 years old.

But maybe it is?

Others remain unconvinced by this conclusion, such as astronomer Scott Bolton of the Southwest Research Institute in Texas. “What I think we might see is not that the storm goes away and then a new storm comes along in roughly the same place,” He told New Scientist magazine. “It would be too much of a coincidence for the storm to occur at exactly the same latitude, or even at a similar latitude. It's possible that what we're really watching is the evolution of the storm.”

Numerical simulations ruled out the model of merging vortices for spot formation; This is likely due to wind currents that produce an elongated atmosphere. Furthermore, in 1879, the Red Spot measured about 24,200 miles (39,000 km) at its longest axis, and it is now about 8,700 miles (14,000 km) long. So, over the following decades, the spot shrank and became more rounded. The latest observations by the Juno mission also revealed that the spot is thin and shallow.

The question of why the great red spot shrinks remains a matter of debate. The team is planning further simulations aimed at reproducing the contracting dynamics and predicting whether the spot will stabilize at a certain size and remain stable or eventually disappear as Cassini's permanent spot did.

Geophysical Research Letters, 2024. DOI: 10.1029/2024GL108993 (About digital IDs).