July 16, 2022
It’s about 3:45 am when the alarm on my phone gradually intrudes upon my slumber, summoning me to an imaging rendezvous with Jupiter that I thought would be a good idea 6 hours earlier. I lay there for a moment and have the internal debate as to whether I really want to do this. A couple of minutes pass and I decide yes, I do want to keep the appointment – it’s worth the effort to see what interesting features might be on display. Donning more appropriate street attire and grabbing the laptop I head out to the driveway where Jupiter hangs like a brilliant beacon above my neighbor’s house.
I wheel the scope out from the garage and pull off the
covers. In my mind I tick down the checklist of tasks to perform before I can
begin imaging. Validate mirror collimation, verify spotting scope alignment,
adjust weight to achieve balance, power up mount & laptop, connect
everything. After a few minutes I fire up the camera and go about
getting Jupiter centered in the field.
As I sharpen the focus my attention is drawn to a very dark
area along the North Equatorial Belt. Pretty weird – the intensity is almost reminiscent
of a shadow transit, but it lacks the crisp, hole-punch appearance that I
normally associate with such an event, seeming more distended. I continue my imaging run for about an
hour and then break down the setup so that I will be ready for the next session.
Later in the day I turn my attention to processing the video capture
into a sharpened image of the planet. As I twiddle with the wavelets I see that the dark area is
a projection off the NEBs extending into the equatorial zone, and the color is
a pronounced dark slate gray. That combination of information allows it to be
classified as a beautiful example of a Jupiter “hot spot”.
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| Jupiter with "Hot Spot" 07/16/2022 |
As documented in John Rogers book The Giant Planet
Jupiter, these blue-gray areas along the NEB’s southern perimeter have been
observed over many decades. Research has found that most of the time there are perhaps a dozen of these features present, spaced roughly every 30⁰ around the planet. From what I have seen from other observers
sending in their images to ALPO, these hot spots are far more prominent
right now. Looking back over the 2021 images I can catch glimpses of these
features in keeping with Roger’s statement, but they were more subtle.
What is a hot spot? Why is it such a different color than we
normally see? Current theory holds that these are areas of high pressure
(sinking air), and as the air warms in its descent the white ammonia crystals
evaporate, allowing us to see deeper into the planet, possibly all the way down
to the level where water clouds can form.
We actually have another reason to be curious about these features because on December 7, 1995, the Galileo atmospheric probe actually entered a hot spot and sent back data for almost an hour, finding less water and helium than expected. Understanding hot spots can help us interpret the data from the probe.
Another interplanetary voyager, Cassini, has also helped to
unravel the mystery of these hot spots. Images taken by Cassini as it flew past
the planet on its way to Saturn have been analyzed, leading to a hypothesis
that a Rossby wave is producing them. Such a wave is undulating up and down in
the atmosphere, generating a hot spot region as it plunges downward, displacing the colder air. There is
a nice NASA video describing the research here.
While it’s not clear if these hot spots will continue to be prominent for the remainder of this Jovian apparition it’s certainly possible. If you are an imager they should be fairly easy to pick up if you are using a scope in the 4-inch (refractor) to 6-inch (reflector) range. Visually a strong outbreak like this one from July 16th should be doable in the same size instrument, especially if you boost the contrast by using a red filter. More subtle ones are likely going to need larger aperture, steady skies, and will also be aided by a red filter. If you do record one you might consider sending your observation to ALPO to document it.
Jupiter reaches opposition next month, a great opportunity
to spend some time examining its features at a reasonable hour of the evening.
Who knows – perhaps you’ll be able to say “Oh course I’ve seen the Great Red
Spot, but have you seen a blue hot spot?”
