APOD: Io: Moon Over Jupiter (2012 Apr 08)

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APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by APOD Robot » Sun Apr 08, 2012 4:10 am

Image Io: Moon Over Jupiter

Explanation: How big is Jupiter's moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the above picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by nstahl » Sun Apr 08, 2012 7:36 am

Great picture, great APOD.

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by orin stepanek » Sun Apr 08, 2012 12:16 pm

Umm! Makes me hungry! :mrgreen:
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by capt618 » Sun Apr 08, 2012 12:45 pm

If you look closely at the image of Io you can see a ring just outside of the moon's surface. Is that a photographic distortion or does it indicate a significant atmosphere?

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Case » Sun Apr 08, 2012 3:15 pm

capt618 wrote:If you look closely at the image of Io you can see a ring just outside of the moon's surface. Is that a photographic distortion or does it indicate a significant atmosphere?
The ring does not show in the full size click-through image, nor in the published TIF image of the same size. It appears to be an image artifact only on the image on the APOD page.
Image

What does appear in the TIF image (which should not have image artifacts like JPEG might have), is a rectangle around Io, like one might see in a bad, amateurish photoshop montage, as if an out-of-focus moon was replaced with a sharper version of the moon. Can you see it? I would have missed it, if it wasn't for the blueish streak to the right of Io. Zoom in further to make it more obvious. :o
Image

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Psnarf » Sun Apr 08, 2012 4:29 pm

The simile to Earth's moon begs the question: Does Io rotate once every 42-hr orbit? Yes, like the Moon, Io rotates once each orbit. Its orbital resonance with Europa and Ganymede creates a tidal bulge of over 300 ft., with the resulting heat generated keeping the mantle pretty-much molten. Other pictures of Io show an active volcano producing an ash cloud that appears bluish, however it can't escape Io's gravity, so such ejecta are closer to the surface than the image artifact.

I imagine there must be something below the visual surface that rotates in sycn with Io? Why else would Io keep the same side always facing Jupiter? Maybe that could help us understand why the Moon keeps the same side facing Earth during its orbit?

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by owlice » Sun Apr 08, 2012 4:35 pm

A closed mouth gathers no foot.

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Chris Peterson » Sun Apr 08, 2012 4:47 pm

Psnarf wrote:I imagine there must be something below the visual surface that rotates in sycn with Io? Why else would Io keep the same side always facing Jupiter? Maybe that could help us understand why the Moon keeps the same side facing Earth during its orbit?
Any pair of bodies in orbit around each other will eventually become tidally locked, unless they are perfectly uniform in their radial density profile, and perfectly spherical... neither of which are possible in the physical world.

Of course, the less massive body will become tidally locked earlier... which is why the Moon keeps the same face to the Earth, but the Earth does not (yet) keep the same face to the Moon.
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Psnarf » Sun Apr 08, 2012 4:47 pm

I can't imagine something the size of Jupiter spinning one rotation every 9.92496 hours.
http://solarsystem.nasa.gov/planets/pro ... tem=Metric [Sidereal Rotation Period (Length of Day)]

I'm getting dizzy, Io spinning at a rate in sych with is 42.5-hour orbit with Jupiter below spinning once every 9.9hours.
http://solarsystem.nasa.gov/planets/pro ... ect=Jup_Io

I'd like to know more about the lightning Io generates. How often does it take to build up a Jupiter-zapping 400,000-volt 3 million ampere lightning bolt? Comparing its distance from Jupiter's surface to the Earth-Moon distance, a lightning bolt that can span that gap must generate radiation as x-rays and cosmic-rays.

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by geckzilla » Sun Apr 08, 2012 5:04 pm

Case wrote:
capt618 wrote:If you look closely at the image of Io you can see a ring just outside of the moon's surface. Is that a photographic distortion or does it indicate a significant atmosphere?
The ring does not show in the full size click-through image, nor in the published TIF image of the same size. It appears to be an image artifact only on the image on the APOD page.
[img]

What does appear in the TIF image (which should not have image artifacts like JPEG might have), is a rectangle around Io, like one might see in a bad, amateurish photoshop montage, as if an out-of-focus moon was replaced with a sharper version of the moon. Can you see it? I would have missed it, if it wasn't for the blueish streak to the right of Io. Zoom in further to make it more obvious. :o
[img]
You should try looking at Hubble's pictures of Jupiter. I tried putting some together like the other space images but the three necessary exposures required for an RGBish image take long enough for the clouds to move significantly so all of the channels are misaligned.
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Chris Peterson » Sun Apr 08, 2012 5:30 pm

Psnarf wrote:I can't imagine something the size of Jupiter spinning one rotation every 9.92496 hours.
Heck, that's an equatorial speed of only 12.6 km/s. Regulus (which is MUCH larger than Jupiter has an equatorial rotation speed of 317 km/s. There are planet-sized stars that rotate hundreds of times per second.
I'd like to know more about the lightning Io generates. How often does it take to build up a Jupiter-zapping 400,000-volt 3 million ampere lightning bolt? Comparing its distance from Jupiter's surface to the Earth-Moon distance, a lightning bolt that can span that gap must generate radiation as x-rays and cosmic-rays.
There are no lightning bolts moving between Io and Jupiter. There is a magnetic flux tube, in which currents can flow. Those are very different things. It isn't a question of building up a charge, which then discharges across a gap, but of a steady dynamo effect which generates a steady current.
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Flase » Mon Apr 09, 2012 2:47 am

Chris Peterson wrote:There are no lightning bolts moving between Io and Jupiter. There is a magnetic flux tube, in which currents can flow. Those are very different things. It isn't a question of building up a charge, which then discharges across a gap, but of a steady dynamo effect which generates a steady current.
It would be nice to use that in a moon base as a power source. Of course Io might not be an easy place to build a base...

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by neufer » Mon Apr 09, 2012 3:39 am

Chris Peterson wrote:
There are no lightning bolts moving between Io and Jupiter. There is a magnetic flux tube, in which currents can flow. Those are very different things. It isn't a question of building up a charge, which then discharges across a gap, but of a steady dynamo effect which generates a steady current.
http://blogs.discovermagazine.com/badastronomy/2008/03/17/ios-footprint-on-jupiter-takes-the-lead/ wrote:
Io’s footprint on Jupiter takes the lead
Discover Magazine

<<Jupiter’s magnetic field is enormous, which is fitting for the King of the Planets. It is far stronger and larger than Earth’s, and, not surprisingly, far more complex. Still, some parts of it are just like home: Jupiter has aurorae. This has been known for years; the interaction of Jupiter’s magnetic field with its atmosphere creates the northern and southern lights in much the same way that it happens on Earth. 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.

Like on Earth, this happens in both of Jupiter’s hemispheres, producing a Jovian equivalent of northern and southern lights. As Jupiter rotates, the connection spot leaves a glowing trail that fades with time, so it looks like a spiral-shaped comet on the top of Jupiter’s atmosphere. By studying that spot and trail, scientists can learn about the planet, the moon, the magnetic field, and their interaction… and get a surprise or two in the process, too. A new paper just released shows that something unexpected has turned up in Hubble images of Io’s UV footprint: a leading spot, ahead of the main bright spot.
ImageImage
That’s weird! The bright spot is the place where Io is connected magnetically to Jupiter, so you simply don’t expect to see a spot ahead of that one. Yet there it is. The scientists noticed something else, too: when there is a leading spot in Io’s footprint in one hemisphere of Jupiter, there are multiple spots in the other hemisphere. This led to think that there is more going on here than previously thought. Evidently, there is some sort of magnetic connection between the north and south pole of Jupiter, directly from Io’s northern footprint to its southern one. Something like what happens in a CRT, beams of electrons are being guided from one pole of Jupiter to the other. Compared to the main connection to Io, the connecting beam is weak, so the leading spot is dim, but it’s there.

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.>>
http://en.wikipedia.org/wiki/Io_%28moon%29#Interaction_with_Jupiter.27s_magnetosphere wrote: <<Io plays a significant role in shaping the Jovian magnetic field. The magnetosphere of Jupiter sweeps up gases and dust from Io's thin atmosphere at a rate of 1 tonne per second. This material is mostly composed of ionized and atomic sulfur, oxygen and chlorine; atomic sodium and potassium; molecular sulfur dioxide and sulfur; and sodium chloride dust. These materials ultimately have their origin from Io's volcanic activity, but the material that escapes to Jupiter's magnetic field and into interplanetary space comes directly from Io's atmosphere. These materials, depending on their ionized state and composition, ultimately end up in various neutral (non-ionized) clouds and radiation belts in Jupiter's magnetosphere and, in some cases, are eventually ejected from the Jovian system.

Surrounding Io (up to a distance of 6 Io radii from the moon's surface) is a cloud of neutral sulfur, oxygen, sodium, and potassium atoms. These particles originate in Io's upper atmosphere but are excited from collisions with ions in the plasma torus (discussed below) and other processes into filling Io's Hill sphere, which is the region where the moon's gravity is predominant over Jupiter. Some of this material escapes Io's gravitational pull and goes into orbit around Jupiter. Over a 20-hour period, these particles spread out from Io to form a banana-shaped, neutral cloud that can reach as far as 6 Jovian radii from Io, either inside Io's orbit and ahead of the satellite or outside Io's orbit and behind the satellite. The collisional process that excites these particles also occasionally provides sodium ions in the plasma torus with an electron, removing those new "fast" neutrals from the torus. However, these particles still retain their velocity (70 km/s, compared to the 17 km/s orbital velocity at Io), leading these particles to be ejected in jets leading away from Io.

Io orbits within a belt of intense radiation known as the Io plasma torus. The plasma in this doughnut-shaped ring of ionized sulfur, oxygen, sodium, and chlorine originates when neutral atoms in the "cloud" surrounding Io are ionized and carried along by the Jovian magnetosphere. Unlike the particles in the neutral cloud, these particles co-rotate with Jupiter's magnetosphere, revolving around Jupiter at 74 km/s. Like the rest of Jupiter's magnetic field, the plasma torus is tilted with respect to Jupiter's equator (and Io's orbital plane), meaning Io is at times below and at other times above the core of the plasma torus. As noted above, these ions' higher velocity and energy levels are partly responsible for the removal of neutral atoms and molecules from Io's atmosphere and more extended neutral cloud. The torus is composed of three sections: an outer, "warm" torus that resides just outside Io's orbit; a vertically extended region known as the "ribbon", composed of the neutral source region and cooling plasma, located at around Io's distance from Jupiter; and an inner, "cold" torus, composed of particles that are slowly spiraling in toward Jupiter. After residing an average of 40 days in the torus, particles in the "warm" torus escape and are partially responsible for Jupiter's unusually large magnetosphere, their outward pressure inflating it from within.[54] Particles from Io, detected as variations in magnetospheric plasma, have been detected far into the long magnetotail by New Horizons. To study similar variations within the plasma torus, researchers measure the ultraviolet-wavelength light it emits. While such variations have not been definitively linked to variations in Io's volcanic activity (the ultimate source for material in the plasma torus), this link has been established in the neutral sodium cloud.

During an encounter with Jupiter in 1992, the Ulysses spacecraft detected a stream of dust-sized particles being ejected from the Jupiter system. The dust in these discrete streams travel away from Jupiter at speeds upwards of several hundred kilometres per second, have an average size of 10 μm, and consist primarily of sodium chloride. Dust measurements by Galileo showed that these dust streams originate from Io, but the exact mechanism for how these form, whether from Io's volcanic activity or material removed from the surface, is unknown.

Jupiter's magnetic field lines, which Io crosses, couples Io's atmosphere and neutral cloud to Jupiter's polar upper atmosphere through the generation of an electric current known as the Io flux tube. This current produces an auroral glow in Jupiter's polar regions known as the Io footprint, as well as aurorae in Io's atmosphere. Particles from this auroral interaction act to darken the Jovian polar regions at visible wavelengths. The location of Io and its auroral footprint with respect to the Earth and Jupiter has a strong influence on Jovian radio emissions from our vantage point: when Io is visible, radio signals from Jupiter increase considerably. The Juno mission, planned for the next decade, should help to shed light on these processes. The Jovian magnetic field lines that do get past Io's ionosphere also induce an electric current, which in turn creates an induced magnetic field, within Io's interior. Io's induced magnetic field is thought to be generated within a partially molten, silicate magma ocean 50 kilometers beneath the moon's surface. Similar induced fields were found at the other Galilean satellites by Galileo, generated within liquid water oceans in the interiors of those moons.
>>
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Chris Peterson » Mon Apr 09, 2012 4:54 am

Flase wrote:It would be nice to use that in a moon base as a power source. Of course Io might not be an easy place to build a base...
Not so easy to get the energy back to where we could use it, either!

The problem with something like this as an energy source is that the actual current density is pretty low. So you'd need a massive collector of some kind. It's the same sort of problem as trying to extract energy from terrestrial auroras- the total currents are very large, but nevertheless very spatially tenuous.
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Flase » Mon Apr 09, 2012 6:04 am

Chris Peterson wrote:Not so easy to get the energy back to where we could use it, either!

The problem with something like this as an energy source is that the actual current density is pretty low. So you'd need a massive collector of some kind. It's the same sort of problem as trying to extract energy from terrestrial auroras- the total currents are very large, but nevertheless very spatially tenuous.
Damn I suppose it would be easier to use the volcanism, then. Otherwise you might have a satellite in a stationary orbit connected to the surface by an ærial.

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Moon Io

Post by hans.grossmann » Mon Apr 09, 2012 9:09 am

When I observe th image of 2012 April 8, it looks like Io had much influence to streamings of Saturn's athmosphere. Is it true?

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Re: Moon Io

Post by neufer » Mon Apr 09, 2012 1:58 pm

hans.grossmann wrote:
When I observe th image of 2012 April 8, it looks like Io had much influence to streamings of Saturn's atmosphere. Is it true?
No.

Io is too far away from Jupiter's atmosphere (not to mention Saturn's).
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Psnarf » Mon Apr 09, 2012 4:12 pm

"Io's orbit, keeping it at more or less a cozy 422,000 km (262,000 miles) from Jupiter, cuts across the planet's powerful magnetic lines of force, thus turning Io into a electric generator. Io can develop 400,000 volts across itself and create an electric current of 3 million amperes. This current takes the path of least resistance along Jupiter's magnetic field lines to the planet's surface, creating lightning in Jupiter's upper atmosphere."
-http://solarsystem.nasa.gov/planets/pro ... ect=Jup_Io

Methinks perhaps the flux tube that generates the auroral glow is different than the lightning generator?

(I don't have access to http://iopscience.iop.org/0034-4885/68/2/R02 referenced in the wiki entry [folks on UofA long-term disability lose their Science Library privileges] . I'd have to drive a couple of hours to my alma mater in order to talk to Dr. Williams in ASU's Geological Sciences building. Dr. Davis, who wrote the NASA article, may have referred to earlier papers?)

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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Chris Peterson » Mon Apr 09, 2012 4:30 pm

Psnarf wrote:"Io's orbit, keeping it at more or less a cozy 422,000 km (262,000 miles) from Jupiter, cuts across the planet's powerful magnetic lines of force, thus turning Io into a electric generator. Io can develop 400,000 volts across itself and create an electric current of 3 million amperes. This current takes the path of least resistance along Jupiter's magnetic field lines to the planet's surface, creating lightning in Jupiter's upper atmosphere."
-http://solarsystem.nasa.gov/planets/pro ... ect=Jup_Io

Methinks perhaps the flux tube that generates the auroral glow is different than the lightning generator?
Auroras are different from upper atmospheric lightning, but I think that both are products of the current flow and magnetic effects of the flux tube. Of course, Jupiter also experiences auroras and lightning that are unrelated to Io.
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by neufer » Mon Apr 09, 2012 4:57 pm

Chris Peterson wrote:
Auroras are different from upper atmospheric lightning, but I think that both are products of the current flow and magnetic effects of the flux tube. Of course, Jupiter also experiences auroras and lightning that are unrelated to Io.
http://en.wikipedia.org/wiki/Atmosphere_of_Jupiter#Storms_and_lightning wrote:
Click to play embedded YouTube video.
<<The storms on Jupiter are similar to thunderstorms on Earth. They reveal themselves via bright clumpy clouds about 1000 km in size, which appear from time to time in the belts' cyclonic regions, especially within the strong westward (retrograde) jets. In contrast to vortices, storms are short-lived phenomena; the strongest of them may exist for several months, while the average lifetime is only 3–4 days. They are believed to be due mainly to moist convection within Jupiter's troposphere. Storms are actually tall convective columns (plumes), which bring the wet air from the depths to the upper part of the troposphere, where it condenses in clouds. A typical vertical extent of Jovian storms is about 100 km; as they extend from a pressure level of about 5–7 bar, where the base of a hypothetical water cloud layer is located, to as high as 0.2–0.5 bar. Storms on Jupiter are always associated with lightning. The imaging of the night–side hemisphere of Jupiter by Galileo and Cassini spacecraft revealed regular light flashes in Jovian belts and near the locations of the westward jets, particularly at 51°N, 56°S and 14°S latitudes. The lightning strikes on Jupiter are on average more powerful than those on Earth. However, they are less frequent; the light power emitted from a given area is similar to that on Earth. A few flashes have been detected in polar regions, making Jupiter the second planet after Earth to exhibit polar lightning.

Every 15–17 years Jupiter is marked by especially powerful storms. They appear at 23°N latitude, where the strongest eastward jet is located. The last time such an event was observed was in March–June 2007. Two storms appeared in the northern temperate belt 55° apart in longitude. They significantly disturbed the belt. The dark material that was shed by the storms mixed with clouds and changed the belt’s color. The storms moved with a speed as high as 170 m/s, slightly faster than the jet itself, hinting at the existence of strong winds deep in the atmosphere.
>>
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Re: APOD: Io: Moon Over Jupiter (2012 Apr 08)

Post by Beyond » Mon Apr 09, 2012 7:18 pm

Lightning, i get such a charge from it!
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