Jupiter’s Great Red Spot – a storm larger than our entire planet – is one of the most visible features of the solar system, probably not long after the invention of the telescope, if not much earlier. However, new evidence shows that the site was created in 1831 and has been mistaken as a continuation of an earlier site from a century before, making the site much, much younger than thought.
Galileo’s adaptation of the telescope for astronomical purposes revealed features such as Jupiter’s moons and sunspots for the first time. As instruments improved, astronomers noticed that Jupiter had dark and light bands parallel to the equator, with sometimes dark spots at the normally white latitudes.
In 1665, Giovanni Cassini, immortalized for discovering the largest hole in Saturn’s rings, was probably the first to report a dark oval that later became known as the “Permanent Spot.” However, a report from 1832 could be about the same thing. Because the spot rotated with Jupiter, it could only be seen for about five hours at a time before disappearing to the other side. However, if the viewer was patient, he always returned, while other places came and went. That is until 1713, when it became invisible and disappeared for a hundred years.
In 1831 the spot was back and was named the Great Red Spot, or so the conventional story goes. Books about the wonders of the solar system typically state that the storm grew so small that it became too small for the modest telescopes of the 18th century.e century to get going again before it rebounds. Considering that the Great Red Spot has changed size many times in nearly two centuries—currently frustrating amateur astronomers by shrinking to about the size of Earth—this story seems very plausible.
However, according to new research, it’s also wrong. Instead, a team led by Professor Agustín Sánchez-Lavega of the Universidad del País Vasco claims that the Permanent Spot and the Great Red Spot are likely unrelated, making the current Spot only 193 years old.
Jupiter painted in 1881 and showed the enormous size of the Spot at that time. Jupiter is upside down due to the telescope used.
Image credits: Thomas Gwyn Elgar Public Domain
The Permanent Spot and the Great Red Spot are both located in Jupiter’s low to mid southern latitudes, leading astronomers to merge the two. However, the Great Red Spot is red, even though we still don’t know why (it also has a blue spot, even though it’s not really blue). We have records from astronomers reporting that they have seen the Permanent Spot many times over the years; the authors of the new study note that none refer to a color, although a painting from 1711 does show a red tint.
Telescopes improved only slowly during the 118 years that Jupiter was relatively spotless, but astronomical giants such as Charles Messier and William Herschel described the planet using telescopes better than their predecessors, without reporting anything at that latitude.
The researchers also argue that the spot we currently see is likely the result of a disruption in the flow of zonal jets north and south of it. This contrasts with the more common explanations: the merger of several smaller eddies or a superstorm. The team modeled the formation of an anticyclonic superstorm on Jupiter, based on Saturn’s giant 100-year storms. Regardless of their assumptions, however, they always ended up with something smaller than the early descriptions of the Great Red Spot. Anti-cyclonic vortices converge on Jupiter, but the authors found that to produce something as big as the Great Red Spot, it would have to rotate much faster than it does today.
Adjusting the age of the Spot would fundamentally change the way we see Jupiter’s atmosphere. If a spot has been there since at least 1665, then it is likely that it was there a long time ago, perhaps millions of years, without anyone having the ability to observe it. The storm, which rises 8 kilometers (5 miles) above the rest of Jupiter’s clouds, would then be considered a nearly permanent part of our solar system, and the current contraction would be expected to reverse soon enough.
On the other hand, if this analysis is correct, the Great Red Spot could be on its last legs, struggling to reach the 200-year mark before disappearing in a puff of ammonia-enriched hydrogen.
The modern Spot is sometimes compared to a giant rolling eye, but it appears that when Jupiter watches the smaller planets, it involves a long blink.
An awful lot happened between 1665 and 1831, so if the Great Red Spot actually formed around the time the reports were restarted, it would be younger than intercity trains (1830) and computers (1822). However, he is slightly older than Jonathan, the oldest living turtle in the world.
The research is open access in Geophysical Research Letters.