Starship Asterisk*

APOD Robot wrote:
Large volcanic moon Io's magnetic funneling of charged particles onto Jupiter is also visible in the southern aurora.

Stephan Schlegel, Joachim Saur wrote in a paper published in JGR Space Physics:

Io's movement relative to the plasma in Jupiter's magnetosphere creates Alfvén waves propagating along the magnetic field lines which are partially reflected along their path. These waves are the root cause for auroral emission, which is subdivided into the Io Footprint (IFP), its tail and leading spot.

sc02492 wrote: ↑Tue Aug 30, 2022 9:38 am The phrase "with 15 times more light-collecting area" as currently written in the caption can be misinterpreted. It refers to field of view, which is a function of the scope's focal length and the camera's sensor size. It is true that JWST has a field of view (how much sky it can capture in a single image) that is 15 times greater than that of Hubble. However, the actual "light collecting area" of JWST's mirror compared to that of Hubble's is (6.5/2.4)^2, which is 7.33 times greater.

Steve

Steve Cannistra
www.starrywonders.com

De58te wrote: ↑Tue Aug 30, 2022 1:40 pm A couple of questions. I read that the JWT can't detect blue visible color, being an infrared camera. So that means that the blue auroras aren't actually a blue color. Does blue mean that it a colder infrared which would make sense since the poles would be colder than the equator. But why is there a blue ring around the planets sides or equatorial regions? Probably because it is the upper atmosphere which is losing heat to space. I think I see that the blue is brighter on the left side than on the right. In the right side there is a narrow dark ring separating the planet's main surface from the upper atmosphere. What is that? Could it be that Jupiter is rotating counterclockwise and the right side has warmer air because it was exposed to the daylight, whereas on the left side it is coming from the cold night side?

bystander wrote: ↑Tue Aug 30, 2022 1:47 pm

De58te wrote: ↑Tue Aug 30, 2022 1:40 pm A couple of questions. I read that the JWT can't detect blue visible color, being an infrared camera. So that means that the blue auroras aren't actually a blue color. Does blue mean that it a colder infrared which would make sense since the poles would be colder than the equator. But why is there a blue ring around the planets sides or equatorial regions? Probably because it is the upper atmosphere which is losing heat to space. I think I see that the blue is brighter on the left side than on the right. In the right side there is a narrow dark ring separating the planet's main surface from the upper atmosphere. What is that? Could it be that Jupiter is rotating counterclockwise and the right side has warmer air because it was exposed to the daylight, whereas on the left side it is coming from the cold night side?

None of what you see is natural color, the image is shot through two near infrared filters (JWST NIRCam), F212N (orange) and F335M (cyan).

johnnydeep wrote: ↑Tue Aug 30, 2022 7:01 pm I second Ann's perplexity about "Io's shadow". I'm still not sure what that really is, or means, or even what the arrow in the pic is pointing to (if meant to refer to something other than the southern aurora).

Discover wrote:...
But Jupiter has something we don't: a volcanically active moon. Io spews sulfur from a series of volcanoes on its surface. The sulfur atoms go up into space, get ionized, and interact with Jupiter's magnetic field as well. Waves of electromagnetic energy are created, and these travel along the magnetic field lines, slamming into Jupiter's atmosphere. Io is, in a way, connected to Jupiter, and you can see this connection, literally, as a bright spot of ultraviolet light on Jupiter.
...

Chris Peterson wrote: ↑Tue Aug 30, 2022 1:57 pm

bystander wrote: ↑Tue Aug 30, 2022 1:47 pm

De58te wrote: ↑Tue Aug 30, 2022 1:40 pm A couple of questions. I read that the JWT can't detect blue visible color, being an infrared camera. So that means that the blue auroras aren't actually a blue color. Does blue mean that it a colder infrared which would make sense since the poles would be colder than the equator. But why is there a blue ring around the planets sides or equatorial regions? Probably because it is the upper atmosphere which is losing heat to space. I think I see that the blue is brighter on the left side than on the right. In the right side there is a narrow dark ring separating the planet's main surface from the upper atmosphere. What is that? Could it be that Jupiter is rotating counterclockwise and the right side has warmer air because it was exposed to the daylight, whereas on the left side it is coming from the cold night side?

None of what you see is natural color, the image is shot through two near infrared filters (JWST NIRCam), F212N (orange) and F335M (cyan).

And even that is not a great way of putting it. The F212N channel has its signal split in some way between the red and green output channels, and the F335M channel has its signal split in some way between the blue and green channels. While such a mapping may produce an aesthetically pleasing image, it is generally a bad idea for any scientific analysis, since it irreversibly conflates the two source channels, resulting in a loss of information. As a rule, it is best if no output (display) channel contains data from more than one input (sensor) channel.

alter-ego wrote: ↑Wed Aug 31, 2022 3:32 am

johnnydeep wrote: ↑Tue Aug 30, 2022 7:01 pm I second Ann's perplexity about "Io's shadow". I'm still not sure what that really is, or means, or even what the arrow in the pic is pointing to (if meant to refer to something other than the southern aurora).

Though fairly complicated, here's a simplified explanation. It's not a new thing, and I must admit I don't recall reading about it before.

Discover wrote:...
But Jupiter has something we don't: a volcanically active moon. Io spews sulfur from a series of volcanoes on its surface. The sulfur atoms go up into space, get ionized, and interact with Jupiter's magnetic field as well. Waves of electromagnetic energy are created, and these travel along the magnetic field lines, slamming into Jupiter's atmosphere. Io is, in a way, connected to Jupiter, and you can see this connection, literally, as a bright spot of ultraviolet light on Jupiter.
...

Click to view full size image

Phil Plait of Bad Astronomy wrote in Discover:

Here's what they think is happening: Io blasts sulfur into space. This forms a torus, a doughnut-shaped region of plasma surrounding Jupiter (yellow-green in the illustration above). The magnetic field of the giant planet ionizes the sulfur.

As Jupiter's magnetic field whips past Io, it connects with the moon, and waves of energy flow from Io to Jupiter, creating the bright footprint spot and trail (not shown, but the stream is in blue).

The spot is connected to its opposite-hemisphere counterpart by the electron beam (shown in red), and that's what creates the leading, fainter spot.

geckzilla wrote: ↑Wed Aug 31, 2022 4:31 am

Chris Peterson wrote: ↑Tue Aug 30, 2022 1:57 pm

bystander wrote: ↑Tue Aug 30, 2022 1:47 pm
None of what you see is natural color, the image is shot through two near infrared filters (JWST NIRCam), F212N (orange) and F335M (cyan).

And even that is not a great way of putting it. The F212N channel has its signal split in some way between the red and green output channels, and the F335M channel has its signal split in some way between the blue and green channels. While such a mapping may produce an aesthetically pleasing image, it is generally a bad idea for any scientific analysis, since it irreversibly conflates the two source channels, resulting in a loss of information. As a rule, it is best if no output (display) channel contains data from more than one input (sensor) channel.

No one should be doing science with *any* of my images. Period. If anyone even thinks about it I'll just direct them straight to the FITS files which they should have known in the first place.