Jupiter’s Great Red Spot – a storm larger than our entire planet – is one of the most visible features of the Solar System, believed to date back to not long after the invention of the telescope, if not much earlier . However, new evidence suggests that it instead originated in 1831 and was mistakenly thought to be a continuation of a previous spot from a century before that, making it much, much younger than previously thought.
Galileo’s adaptation of the telescope for astronomical purposes famously 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 dark spots sometimes appearing in the normally white latitudes.
In 1665, Giovanni Cassini, immortalized for discovering the largest gap in Saturn’s rings, was probably the first to report a dark oval, subsequently known as the “Permanent Spot.” However, a report from 1832 may 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 into the far country, but provided the viewer was patient, it would always return as other spots came and went. . That is until 1713, when it faded into invisibility and disappeared for 100 years.
In 1831, the spot returned and was named the Great Red Spot, or so the conventional story goes. Books about the wonders of the solar system usually claim that the storm shrunk to be too small for the modest telescopes of the 18th century to take before you bounce. Given that the Great Red Spot has changed in size many times over the course of nearly two centuries—currently disappointing amateur astronomers by shrinking to the size of Earth—this story seems very plausible.
However, according to new research, this is also wrong. Instead, a team led by Professor Agustin Sánchez-Lavega of the Universidad del País Vasco argued that the Persistent Spot and the Great Red Spot are likely unrelated, making the current spot only 193 years old.
Jupiter, painted in 1881, shows the enormous size of the Spot at the time. Jupiter is upside down as a result of the telescope used.
Image credit: Thomas Gwynne Elgar, public domain
The Permanent Spot and the Great Red Spot are located in Jupiter’s low to mid-southern latitudes, leading astronomers to conflate the two. The Great Red Spot, however, is red, although we still don’t know why (it also has a blue spot, although it’s not really blue). We have records of astronomers reporting seeing the Fixed Spot many times over the years; the authors of the new study note that none refer to color, although a painting made in 1711 shows a red hue.
Telescopes improved slowly during the 118 years when Jupiter was relatively clear, but giants of astronomy such as Charles Messier and William Herschel described the planet using telescopes better than their predecessors, reporting nothing at this latitude.
The researchers also say that the Spot we see now is likely the result of a disruption in the flow of zonal jets north and south of it. This contrasts with more common explanations: the merging of multiple smaller eddies or a super-storm. The team modeled the formation of Jupiter’s anticyclone superstorm based on Saturn’s giant 100-year storms. Regardless of their assumptions, however, they always got something less than the early descriptions of the Great Red Spot. Anticyclonic eddies coalesce on Jupiter, but the authors found that to produce something as large as the Great Red Spot, it would have to spin much faster than it currently does.
Readjusting the age of the spot would fundamentally change the way we see Jupiter’s atmosphere. If a spot has existed since at least 1665, then it was probably there a long time ago, perhaps millions of years, without anyone having the capacity to observe it. The storm, rising 8 kilometers (5 miles) above the rest of Jupiter’s clouds, would then be considered a near-permanent part of our Solar System, and its current contraction would be expected to reverse soon enough.
On the other hand, if this analysis is correct, the Great Red Spot may be on its last legs, struggling to reach the 200-year mark before disappearing into a cloud of ammonia-enriched hydrogen.
The modern spot is sometimes compared to a giant spinning eye, but it seems that if Jupiter is tracking the smaller planets, it comes with long blinks.
An awful lot happened between 1665 and 1831, so if the Great Red Spot really did form by the time the reports restarted, it would be younger than intercity railroads (1830) and computers (1822 d.). However, she is slightly older than Jonathan, the world’s oldest living turtle.
The research is open access in Geophysical Research Letters.
