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.
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.>>
[quote="Chris Peterson"]
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.[/quote]
[quote=" http://blogs.discovermagazine.com/badastronomy/2008/03/17/ios-footprint-on-jupiter-takes-the-lead/"]
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.
[img]http://blogs.discovermagazine.com/badastronomy/files/2008/io_leadingspot.jpg[/img][img]http://blogs.discovermagazine.com/badastronomy/files/2008/io_jupiter_connection.jpg[/img]
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.>>[/quote][quote=" http://en.wikipedia.org/wiki/Io_%28moon%29#Interaction_with_Jupiter.27s_magnetosphere"]
[float=right][img3="[b][color=#0000FF]Schematic of Jupiter's magnetosphere and the components influenced by Io (near the center of the image): the plasma torus (in red), the neutral cloud (in yellow), the flux tube (in green), and magnetic field lines (in blue).[/color][/b]"]http://upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Jupiter_magnetosphere_schematic.jpg/800px-Jupiter_magnetosphere_schematic.jpg[/img3][/float]<<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.
[b][color=#0000FF]
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. [u]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.[/u] 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.[/color][/b]>>[/quote]