APOD: Aurorae and Lightning on Jupiter (2021 Mar 24)

[APOD Robot]

Aurorae and Lightning on Jupiter

Explanation: Why does so much of Jupiter's lightning occur near its poles? Similar to Earth, Jupiter experiences both aurorae and lightning. Different from Earth, though, Jupiter's lightning usually occurs near its poles -- while much of Earth's lightning occurs near its equator. To help understand the difference, NASA's Juno spacecraft, currently orbiting Jupiter, has observed numerous aurora and lightning events. The featured image, taken by Juno's Stellar Reference Unit camera on 2018 May 24, shows Jupiter's northern auroral oval and several bright dots and streaks. An eye-catching event is shown in the right inset image -- which is a flash of Jupiter's lightning -- one of the closest images of aurora and lightning ever. On Earth (which is much nearer to the Sun than Jupiter), sunlight is bright enough to create, by itself, much stronger atmospheric heating at the equator than the poles, driving turbulence, storms, and lightning. On Jupiter, in contrast, atmospheric heating comes mostly from its interior (as a remnant from its formation), leading to the hypothesis that more intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

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[madtom1999]

The magnetic field concentrates the solar winds ions into the upper atmosphere forming the aurora. I wonder if Jupiter'.s magnetic field is large and powerful enough to focus cosmic rays at the poles too and these act as triggers for the lightning

[Jerome]

This APOD features en extensive ring system.
The image assembles genuine images and computer-added coordinate lines, but I can't tell if the ring system are part of the genuine image, and if yes, at which wavelength. I had never seen photos featuring Jupiter's rings so visible from top - compare e.g. with Galileo's overexposed and New Horizons' edge-on images here: https://www.nasa.gov/centers/goddard/mu ... rings.html

I would be very grateful to see a next APOD on new images of Jupiter's rings

Thank you APOD team for the continued service making us every morning a little less ignorant of our Universe.

J.

[JohnD]

Do cosmic rays trigger lightning on Earth?

And how is lightning generated on Jupiter? I thought that theory says terrestrial lightning was raindrops (hailstones?) striking each other in turbulence and causing a charge seperation. If so, and no reason why not (?), various ice particles on Jupiter could do the same, and more likely to do so at the colder poles?
John

[VictorBorun]

The magnetic field concentrates the solar winds ions into the upper atmosphere forming the aurora. I wonder if Jupiter'.s magnetic field is large and powerful enough to focus cosmic rays at the poles too and these act as triggers for the lightning

I thought a magnificent lightning needs a good insulator media like dense atmosphere with no ions.
A cosmic or solar shower at a magnetic pole should sabotage the lightnings then.

[orin stepanek]

APOD

that more intense equatorial sunlight reduces temperature differences between upper atmospheric levels

I liked the dive into the Red Spot showing the heat differences with the altitude changes!

[neufer]

Cosmic flux versus particle energy

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The magnetic field concentrates the solar winds ions into the upper atmosphere forming the aurora. I wonder if Jupiter'.s magnetic field is large and powerful enough to focus cosmic rays at the poles too and these act as triggers for the lightning

<<The boundary separating the denser and colder [250–750 km/s] solar wind's plasma from the hotter and less dense one within Jupiter's magnetosphere is called the magnetopause. The distance from the magnetopause to the center of the planet is from 45 to 100 R_J at the subsolar point—the unfixed point on the surface at which the Sun would appear directly overhead to an observer.>>

If the solar wind were ~100 times faster [25,000–75,000 km/s] (with ~100 times larger gyroradii) Jupiter's magnetosphere would probably not be able to prevent solar wind protons from (more or less) directly penetrating down to the surface. Hence relativistic Gev⁺ cosmic rays [~300,000 km/s] also penetrate (more or less) directly down to Jupiter's surface with minimal focusing.

<<Cosmic rays have been implicated in the triggering of electrical breakdown in lightning. It has been proposed that essentially all lightning is triggered through a relativistic process, or "runaway breakdown", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.>>

[johnnydeep]

Aurorae and Lightning on Jupiter

Explanation: Why does so much of Jupiter's lightning occur near its poles? Similar to Earth, Jupiter experiences both aurorae and lightning. Different from Earth, though, Jupiter's lightning usually occurs near its poles -- while much of Earth's lightning occurs near its equator. To help understand the difference, NASA's Juno spacecraft, currently orbiting Jupiter, has observed numerous aurora and lightning events. The featured image, taken by Juno's Stellar Reference Unit camera on 2018 May 24, shows Jupiter's northern auroral oval and several bright dots and streaks. An eye-catching event is shown in the right inset image -- which is a flash of Jupiter's lightning -- one of the closest images of aurora and lightning ever. On Earth (which is much nearer to the Sun than Jupiter), sunlight is bright enough to create, by itself, much stronger atmospheric heating at the equator than the poles, driving turbulence, storms, and lightning. On Jupiter, in contrast, atmospheric heating comes mostly from its interior (as a remnant from its formation), leading to the hypothesis that more intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

It wasn't at all clear to me where the lightning was in the pic. Luckily, the "featured image" link tells us. I wasn't nery impressed As for the several "bright dots and streaks", the link says they are "signatures of high energy relativistic electrons from polar beams that are penetrating the camera."

Lightning "Flash", or "Dot" on Jupiter

[MarkBour]

Just checking that I understood the caption. If I did, then there's a switch in the last sentence. Wouldn't the hypothesis be:

leading to the hypothesis that more less intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

[neufer]

Just checking that I understood the caption.

If I did, then there's a switch in the last sentence. Wouldn't the hypothesis be:

leading to the hypothesis that more less intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

The caption as stated is probably correct... although based on rather simplified assumptions.

The Earth's dynamically stable stratosphere is maintained due to rapid photolysis & reformation of ozone by solar UV radiation. Presumably, Jupiter's own dynamically stable stratospheric cap is also maintained by similar solar UV radiation processes while its warm (400+K ) unstable "surface" temperature is primarily heated by internal thermal processes.

<<The mechanism describing the formation of the ozone layer was described by British mathematician Sydney Chapman in 1930. Molecular oxygen absorbs high energy sunlight in the UV-C region, at wavelengths shorter than about 240 nm. Radicals produced from the homolytically split oxygen molecules combine with molecular oxygen to form ozone. Ozone in turn is photolysed much more rapidly than molecular oxygen as it has a stronger absorption that occurs at longer wavelengths, where the solar emission is more intense. Ozone (O₃) photolysis produces O and O₂. The oxygen atom product combines with atmospheric molecular oxygen to reform O₃, releasing heat. The rapid photolysis and reformation of ozone heats the stratosphere resulting in a temperature inversion. This increase of temperature with altitude is characteristic of the stratosphere; its resistance to vertical mixing means that it is stratified. Within the stratosphere temperatures increase with altitude (see temperature inversion); the top of the stratosphere has a temperature of about 270 K. This vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere.>>

Vertical structure of the atmosphere of Jupiter. Note that the temperature drops together with altitude above the tropopause. The Galileo atmospheric probe stopped transmitting at a depth of 132 km below the 1 bar "surface" of Jupiter.

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<<The atmosphere of Jupiter is classified into four layers, by increasing altitude: the troposphere, stratosphere, thermosphere and exosphere. Unlike the Earth's atmosphere, Jupiter's lacks a mesosphere. Jupiter does not have a solid surface, and the lowest atmospheric layer, the troposphere, smoothly transitions into the planet's fluid interior. This is a result of having temperatures and the pressures well above those of the critical points for hydrogen and helium, meaning that there is no sharp boundary between gas and liquid phases. Hydrogen becomes a supercritical fluid at a pressure of around 12 bar.

Since the lower boundary of the atmosphere is ill-defined, the pressure level of 10 bars, at an altitude of about 90 km below 1 bar with a temperature of around 340 K, is commonly treated as the base of the troposphere.

The vertical temperature gradients in the Jovian atmosphere are similar to those of the atmosphere of Earth. The temperature of the troposphere decreases with height until it reaches a minimum at the tropopause, which is the boundary between the troposphere and stratosphere. On Jupiter, the tropopause is approximately 50 km above the visible clouds (or 1 bar level), where the pressure and temperature are about 0.1 bar and 110 K.

Jupiter's troposphere contains a complicated cloud structure. The upper clouds, located in the pressure range 0.6–0.9 bar, are made of ammonia ice. Below these ammonia ice clouds, denser clouds made of ammonium hydrosulfide ((NH₄)SH) or ammonium sulfide ((NH₄)₂S, between 1–2 bar) and water (3–7 bar) are thought to exist. There are no methane clouds as the temperatures are too high for it to condense. The water clouds form the densest layer of clouds and have the strongest influence on the dynamics of the atmosphere. This is a result of the higher condensation heat of water and higher water abundance as compared to the ammonia and hydrogen sulfide (oxygen is a more abundant chemical element than either nitrogen or sulfur). Various tropospheric (at 200–500 mbar) and stratospheric (at 10–100 mbar) haze layers reside above the main cloud layers. The latter are made from condensed heavy polycyclic aromatic hydrocarbons or hydrazine, which are generated in the upper stratosphere (1–100 μbar) from methane under the influence of the solar ultraviolet radiation (UV).>>

[heehaw]

I wonder why there does not seem to be interstellar lightning: bolts from interstellar cloud to interstellar cloud.

[Chris Peterson]

I wonder why there does not seem to be interstellar lightning: bolts from interstellar cloud to interstellar cloud.

Because the fields are not large enough? Because lightning requires a moderately dense medium compared with the hard vacuum found between interstellar clouds?

[Jupiter ring jokes]

C'mon, Jupiter's ring is not like that. But there seems to be some kind of tradition or inside joke among the team behind the Juno instrument which does aurorae, the SRU, about putting a Saturn-style ring system around Jupiter. I thought it was an instrument baffle or something, but then there's this artist concept, among others -- apparently too big to insert here, but see it at https://www.jpl.nasa.gov/images/junos-p ... ts-concept.

Hmm, sure, JPL, go ahead and put moustaches on the planets. Why not? And of course Jupiter would be very grand with a big multiring system, but we'd have to blow one of the satellites to get it. And that would be terribly uncool.

[Jupiter ring jokes]

I seem to stand corrected by https://en.wikipedia.org/wiki/Rings_of_Jupiter, Jupiter has pretty broad gossamer rings after all. Now, surely the light angle, the light intensification or the wavelength have to be pretty special for them to show up like that. If so, maybe those lightning flashes are blindingly bright only if you stare at them with UV eyes. (And that would be entirely OK, of course, UV eyes are kinda cool in fact).

[Chris Peterson]

I seem to stand corrected by https://en.wikipedia.org/wiki/Rings_of_Jupiter, Jupiter has pretty broad gossamer rings after all. Now, surely the light angle, the light intensification or the wavelength have to be pretty special for them to show up like that. If so, maybe those lightning flashes are blindingly bright only if you stare at them with UV eyes. (And that would be entirely OK, of course, UV eyes are kinda cool in fact).

This image was made with the spacecraft's star tracker, from a distance of only 60,000 km. With a FOV of 20°, it can't come close to capturing Jupiter's ring system, or even most of the planet. Outside of the auroral oval itself, pretty much everything else in this image is superimposed to provide are reference.

[madtom1999]

The magnetic field concentrates the solar winds ions into the upper atmosphere forming the aurora. I wonder if Jupiter'.s magnetic field is large and powerful enough to focus cosmic rays at the poles too and these act as triggers for the lightning

I thought a magnificent lightning needs a good insulator media like dense atmosphere with no ions.
A cosmic or solar shower at a magnetic pole should sabotage the lightnings then.

Fluorescent lights are evacuated for a reason - you need a mean free path that is large enough for a charged particle to be accelerated sufficiently to be able to ionise another molecule and so create a cascade. In a dense atmosphere like Jupiter's the mean free path is not going to be much more than one or two molecules and so the electric field needed to instigate lightning is just absolutely massive which is why there is little lightning elsewhere on Jupiter - the charges are dissipated by the general atmospheric movements. When something with the heft of a cosmic ray can create long ionised path then the charge difference can be dissipated along it.

[VictorBorun]

In a dense atmosphere like Jupiter's the mean free path is not going to be much more than one or two molecules and so the electric field needed to instigate lightning is just absolutely massive which is why there is little lightning elsewhere on Jupiter - the charges are dissipated by the general atmospheric movements. When something with the heft of a cosmic ray can create long ionised path then the charge difference can be dissipated along it.

So the Jovian air is almost a soup, or 1/10 of liquid water density?
So it's a too solid insulator for a storm and a solar wind blast is welcomed to help lightnings break through?
Wow.

[MarkBour]

Just checking that I understood the caption.

If I did, then there's a switch in the last sentence. Wouldn't the hypothesis be:

leading to the hypothesis that more less intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

The caption as stated is probably correct... although based on rather simplified assumptions.

... followed a lot of explanation of temperature in the Jovian atmosphere.

But none of that explanation made me disbelieve my statement. Clearly sunlight at the equator of Jupiter is far less intense than at the equator of Earth. So, clearly, the temperature gradient effects of sunlight on Jupiter's atmosphere would be less. And fewer temperature differences are what *might* be leading to less equatorial lightning in Jupiter's atmosphere.

[Forrest White]

Is it Jupiter’s Great Red Spot which was noticed in the mid-1800’s?

[neufer]

Is it Jupiter’s Great Red Spot which was noticed in the mid-1800’s?

Donato Creti's 1711 _Charity_

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<<The Great Red Spot has been observed since 5 September 1831. By 1879 over 60 observations were recorded. After it came into prominence in 1879, it has been under continuous observation.

The first sighting of the Great Red Spot is often credited to Robert Hooke, who described a spot on the planet in May 1664. However, it is likely that Hooke's spot was in another belt altogether (the North Equatorial Belt, as opposed to the current Great Red Spot's location in the South Equatorial Belt). Much more convincing is Giovanni Cassini's description of a "permanent spot" the following year. With fluctuations in visibility, Cassini's spot was observed from 1665 to 1713, but the 118-year observational gap makes the identity of the two spots inconclusive. The older spot's shorter observational history and slower motion than the modern spot makes it difficult to conclude that they are the same.

A minor mystery concerns a Jovian spot depicted in a 1711 canvas by Donato Creti, which is exhibited in the Vatican. Part of a series of panels in which different (magnified) heavenly bodies serve as backdrops for various Italian scenes, and all overseen by the astronomer Eustachio Manfredi for accuracy, Creti's painting is the first known to depict the Great Red Spot as red. No Jovian feature was explicitly described in writing as red before the late 19th century.>>