Jupiter’s Great Red Spot extending upward as it shrinks

Jupiter’s ‘Great Red Spot’ [image credit: NASA]

It seems to be turning into the not-so-great orange spot. Could this be a feature of climate change Jupiter-style?

Though once big enough to swallow three Earths with room to spare, Jupiter’s Great Red Spot has been shrinking for a century and a half, says Astronomy Now. Nobody is sure how long the storm will continue to contract or whether it will disappear altogether.

A new study suggests that it hasn’t all been downhill, though. The storm seems to have increased in area at least once along the way, and it’s growing taller as it gets smaller.

“Storms are dynamic, and that’s what we see with the Great Red Spot. It’s constantly changing in size and shape, and its winds shift, as well,” said Amy Simon, an expert in planetary atmospheres at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland, and lead author of the new paper, published in the Astronomical Journal.

Observations of Jupiter date back centuries, but the first confirmed sighting of the Great Red Spot was in 1831. (Researchers aren’t certain whether earlier observers who saw a red spot on Jupiter were looking at the same storm.)

Keen observers have long been able to measure the size and drift of the Great Red Spot by fitting their telescopes with an eyepiece scored with crosshairs. A continuous record of at least one observation of this kind per year dates back to 1878.

Simon and her colleagues drew on this rich archive of historical observations and combined them with data from NASA spacecraft, starting with the two Voyager missions in 1979. In particular, the group relied on a series of annual observations of Jupiter that team members have been conducting with NASA’s Hubble Space Telescope as part of the Outer Planets Atmospheres Legacy, or OPAL, project, based in California.

The team traced the evolution of the Great Red Spot, analysing its size, shape, colour and drift rate. They also looked at the storm’s internal wind speeds, when that information was available from spacecraft.

The new findings indicate that the Great Red Spot recently started to drift westward faster than before. The storm always stays at the same latitude, held there by jet streams to the north and south, but it circles the globe in the opposite direction relative to the planet’s eastward rotation. Historically, it’s been assumed that this drift is more or less constant, but in recent observations, the team found the spot is zooming along much faster.

The study confirms that the storm has been decreasing in length overall since 1878 and is big enough to accommodate just over one Earth at this point. But the historical record indicates the area of the spot grew temporarily in the 1920s.

“There is evidence in the archived observations that the Great Red Spot has grown and shrunk over time,” said co-author Reta Beebe, an emeritus professor at New Mexico State University in Las Cruces. “However, the storm is quite small now, and it’s been a long time since it last grew.”

Continued here.
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Video here.