The Earth-sized storm on Jupiter known as the red spot was thought by many to have been first observed in 1665, but it turns out that may have been an entirely different enormous storm, with today's storm dating back only to 1831
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| Jupiter's red spot as captured by NASA's Juno Spacecraft (Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstad/Sean Doran) |
Jupiter’s Great Red Spot may be younger than many astronomers thought. It is commonly accepted that the enormous storm was first observed by Giovanni Cassini in 1665, but it turns out that the spot Cassini saw was probably a different one to the vortex visible now.
The Great Red Spot, a storm larger than the planet Earth, has been continuously observable since 1831. But an enormous storm was also visible at the same location on Jupiter from 1665 to 1713, and astronomers have been debating whether the two tempests are in fact one and the same for decades. “There has been a lot of confusion and about who observed it for the first time,” says Agustín Sánchez-Lavega at the University of the Basque Country in Spain.
Sánchez-Lavega and his colleagues performed a systematic review and analysis of all the available observations of the earlier storm – which was known as the Permanent Spot – preserved in astronomers’ drawings. They then compared them to early photographs and newer images of the Great Red Spot we see today. They found that, if the drawings are accurate, the Permanent Spot was far smaller than the Great Red Spot – its diameter would have had to grow at a rate of about 160 kilometres per year from 1713 to 1879 for the two to be consistent.
But none of Jupiter’s vortices have been shown to grow in such a rapid and sustained manner. Moreover, recent observations show that the Great Red Spot appears to be shrinking, not growing. This and other small inconsistencies, along with the 118-year gap in observations, led the researchers to conclude that the two spots are not the same.
However, Scott Bolton at the Southwest Research Institute in Texas says it is difficult to make secure conclusions based on hand-drawn pictures of a distant world. “What I think we may be seeing is not so much that the storm went away and then a new one came in almost the same place – it would be a very big coincidence to have it occur at the same exact latitude, or even a similar latitude,” he says. “It could be that what we’re really watching is the evolution of the storm.” That still wouldn’t account for the recent shrinking, though.
Even if the Great Red Spot is younger than we thought, it is still far longer-lasting than any other storm we have ever seen. But if it isn’t, it could be mind-bogglingly old. “When we’re looking at something on the scale of a whole planet, it’s billions of years old, and we’re just looking at a brief snapshot, even if hundreds of years seems like a long time to us,” says Bolton. “If this was actually the same storm that Cassini saw, even in a different form, it could be much older than the 1600s.”
On the other hand, if the two spots seen on Jupiter are wholly different storms, “an implication… is that the modern Great Red Spot must have formed or appeared during the late 18th century or just after,” says Peter Read at the University of Oxford. “Its formation may therefore have been amenable to observation, at least in principle.” If that is the case, we might have the opportunity to search for hints of the birth of the Great Red Spot in the historical record, closing the case of the two spots once and for all.
Journal reference:
Geophysical Research Letters DOI: 10.1029/2024GL108993
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