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A person could be forgiven when looking at Jupiter's Red Spot storm for concluding that it doesn't move. That it's geologically locked in place. But is it?

I know it's a stretch to use the phrase "geologically locked in place" when referring to a gas giant. So let me ask the question in a little different way.

As we observe Jupiter's rotation, does the storm show up in the very same spot on each rotation or does the spot move around, sometimes appearing more quickly on one rotation and later on the next? I suspect that the Red Spot can't move latitudinaly as it's likely bound to the band of turbulence it's in. But can it move "longitudinally" within that band or does it literally stay in one place, facing the Sun every 9 hours and 50 minutes (assuming it's equatorial, you get my point) like clockwork?

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  • $\begingroup$ Looks the face of Jupiter always the same seen from Earth? $\endgroup$
    – Deschele Schilder
    Commented Jul 30, 2021 at 15:39
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    $\begingroup$ As Jupiter is not solid (in the way that earth is), I’m not sure there is such a thing as “geological position”. $\endgroup$
    – RBarryYoung
    Commented Jul 30, 2021 at 20:48
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    $\begingroup$ @RBarryYoung, Jupiter may or may not have a solid core, but the magnetic field (and thus, presumably, the core) does have a well-defined period of rotation. $\endgroup$
    – Mark
    Commented Jul 30, 2021 at 22:13
  • $\begingroup$ Linguistic nitpick: since ‘geology’ is specifically about the study of Earth, wouldn't the study of Jupiter's composition be called something else (possibly with ‘Jove-’ as the root)? $\endgroup$
    – gidds
    Commented Aug 2, 2021 at 0:36

3 Answers 3

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It does drift relative to other parts of the atmosphere. The lack of a surface makes defining the actual rotation period of Jupiter rather difficult. The currently accepted value of 9h:55m:29.7s is based on the average rotation of the interior, inferred from magnetic field measurements.

The Red Spot was previously used to define the rotation period, averaging at 9h:55m:42s. With no surface features to break up the winds, this period is quite stable.

In the longer term the drift speed does vary. The spot has "lapped" the planet at least 10 times since the early nineteenth century. Its drift rate has changed dramatically over the years and has been linked to the brightness of the South Equatorial Belt and the presence or absence of a South Tropical Disturbance.

The timelapse by Voyager shows the relative movement in different bands.

(Jupiter rotation animation)

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    $\begingroup$ When you say "lapped", that implies that for long periods of time, it would not be visible from any Earthbound (including Earth-orbiting) telescope, due to being on the far side of the planet? I'm not sure if I've seen many pictures of Jupiter without the Spot. Is it just because the last time it was not visible from Earth predates the technology to view and photograph it? $\endgroup$
    – Darrel Hoffman
    Commented Jul 30, 2021 at 14:28
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    $\begingroup$ @DarrelHoffman Jupiter itself rotates every 10 hours, so the red spot is not always visible from Earth. But if you are going to publish a picture of Jupiter, would you pick one that didn't show its most prominent and popular feature? $\endgroup$
    – Michael Richardson
    Commented Jul 30, 2021 at 14:35
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    $\begingroup$ @MichaelRichardson Sorry, right, I'm just having trouble understanding how we decide it's "lapped" the planet, when there aren't any fixed points to measure its rotation by. $\endgroup$
    – Darrel Hoffman
    Commented Jul 30, 2021 at 14:39
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    $\begingroup$ Satellites measure the rotation speed of the magnetosphere, this is linked to the conductive interior of Jupiter and can be considered to be the rotation of the planet's interior. agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009GL040094 $\endgroup$
    – James K
    Commented Jul 30, 2021 at 16:42
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    $\begingroup$ @DarrelHoffman You've not seen any Jupiter photos without the red spot, because most likely all the photos of Jupiter you've seen have come from sources like news stories, or museum displays, or even textbooks in segments not actually specifically about studying Jupiter's weather, and people who put together such works don't use pictures of the non-red-spot side of Jupiter, because they want people to be able to recognize it as Jupiter, and the red spot is how most of the human population does that. $\endgroup$
    – Matthew Najmon
    Commented Aug 1, 2021 at 17:36
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Yes, as with all other storms, the Great Red Spot is dynamic, so it constantly changes its size and shape and it shifts and drifts and is not just "locked in a definite position". According to nasa.gov:

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.

If we take real numbers then according to JUPOS, it is predicted that the Red Spot (which was at Jovian System II longitude 2° in July 2021) will continue to drift 1.75° per month (source).

For more information, see my answer here.

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  • $\begingroup$ i love JUPOS !! i'm going to add an additional JUPOS answer. $\endgroup$
    – giardia
    Commented Dec 4, 2021 at 7:29
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There is a great answer to this on the http://jupos.org site. The updated graph is at the link https://jupos.privat.t-online.de/img/Grs.GIF, but it is a vintage site so browsers may have some issues with security certificates. Here is the version currently available in dec. 2021:

plot of GRS longitude vs. time

To understand the plot, it's helpful to know that time is increasing downwards, and the x-axis is the great red spot (GRS) location in system II longitude. It's shown as a huge collection of points, each one measured on an image taken by an amateur astronomer.

System II was defined as the average rotation rate of the GRS, so if the spot didn't move around, all the dots would be arranged in a straight vertical line. Instead, you can see wiggles (in particular a 90-day oscillation), and an overall slope. The slope means that the GRS drift rate has changed in the years following the creation of the system II longitude system.

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  • $\begingroup$ Interesting! Do you know why is there a gap in early 2021? $\endgroup$
    – Jean-Marie Prival
    Commented Dec 7, 2021 at 14:28
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    $\begingroup$ @Jean-MariePrival Jupiter was behind the Sun as seen from Earth. Closest approach was on January 29th at approximately 0.5° angular distance. $\endgroup$
    – Karsten Kretschmer
    Commented Dec 7, 2021 at 15:21
  • $\begingroup$ @KarstenKretschmer Makes sense, thanks! $\endgroup$
    – Jean-Marie Prival
    Commented Dec 7, 2021 at 15:52

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