APOD: Io in True Color (2014 Mar 30)

[APOD Robot]

Io in True Color

Explanation: The strangest moon in the Solar System is bright yellow. This picture, an attempt to show how Io would appear in the "true colors" perceptible to the average human eye, was taken in 1999 July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003. Io's colors derive from sulfur and molten silicate rock. The unusual surface of Io is kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons. The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface. Io's volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.

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[Nitpicker]

Such a great image and such an interesting Moon. I imagine it's a rather smelly place, though.

[geckzilla]

I'd like to see what a fresh impact would kick up. How deep does this sulfur go? As it is, the only craters I see here are fiery calderas.

[Jandotto]

There seem to be several volcanic plumes evident - or are they lava flows? [E.g. on equator left, NE of equator and SW of equator]

[neufer]

I'd like to see what a fresh impact would kick up. How deep does this sulfur go? As it is, the only craters I see here are fiery calderas.

[b][size=125][color=#0000FF]One model of the possible interior composition of Io with an inner iron or iron sulfide core (in gray), a partially molten silicate mantle (in orange) , and[/color] [color=#FF4000]a thin outer silicate crust (in brown)[/color][/size][/b]

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<<Composed primarily of silicate rock and iron, Io is closer in bulk composition to the terrestrial planets than to other satellites in the outer Solar System, which are mostly composed of a mix of water ice and silicates. Io has a density of 3.53 g/cm³, the highest of any moon in the Solar System; significantly higher than the other Galilean satellites and higher than the Moon (3.35 g/cm³). Models based on the Voyager and Galileo measurements of Io's mass, radius, and quadrupole gravitational coefficients (numerical values related to how mass is distributed within an object) suggest that its interior is differentiated between a silicate-rich crust and mantle and an iron- or iron-sulfide-rich (e.g., fool's gold) core. Io's metallic core makes up approximately 20% of its mass. Depending on the amount of sulfur in the core, the core has a radius between 350 & 650 km if it is composed almost entirely of iron, or between 550 & 900 km for a core consisting of a mix of iron & sulfur (e.g., fool's gold). Galileo's magnetometer failed to detect an internal, intrinsic magnetic field at Io, suggesting that the core is not convecting.

Modeling of Io's interior composition suggests that the mantle is composed of at least 75% of the magnesium-rich mineral forsterite similar to that of L-chondrite and LL-chondrite meteorites, with higher iron content than the Moon or Earth, but lower than Mars. Re-analysis of Galileo magnetometer data in 2009 revealed the presence of an induced magnetic field at Io, requiring a magma ocean 50 km below the surface. It is estimated that the temperature in the magma ocean reaches 1,200 °C. The lithosphere of Io, composed of basalt and sulfur deposited by Io's extensive volcanism, is at least 12 km thick, but is likely to be less than 40 km thick.

[b][color=#0000FF]Io's colorful appearance is the result of various volcanic materials.[/color][/b]

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Io's colorful appearance is the result of various volcanic materials. Sulfur dioxide frost is ubiquitous across the surface of Io, forming large regions covered in white or grey materials. Sulfur is also seen in many places across Io, forming yellow to yellow-green regions. Sulfur deposited in the mid-latitude and polar regions is often radiation damaged, breaking up normally stable cyclic 8-chain sulfur. This radiation damage produces Io's red-brown polar regions. Plume deposits on Io are often colored red or white depending on the amount of sulfur and sulfur dioxide in the plume. Generally, plumes formed at volcanic vents from degassing lava contain a greater amount of S₂, producing a red "fan" deposit, or in extreme cases, large red rings. These red deposits consist primarily of sulfur (generally 3- and 4-chain molecular sulfur), sulfur dioxide, and perhaps Cl₂SO₂. Plumes formed at the margins of silicate lava flows (through the interaction of lava and pre-existing deposits of sulfur and sulfur dioxide) produce white or gray deposits.

Compositional mapping and Io's high density suggest that Io contains little to no water, though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons. This lack of water is likely due to Jupiter being hot enough early in the evolution of the Solar System to drive off volatile materials like water in the vicinity of Io, but not hot enough to do so farther out.>>

[Eleanor S]

Does the APOD community have a way to show the 'glow in the dark' phenomenon? It would certainly show the active volcanos. Thank you for this picture of Io!

[Ironwood]

"Some of Io's volcanic lava is so hot it glows in the dark." I picture all lava as glowing in the dark, mainly because lava is red hot molten rock. If something glows, it glows in the light as well as the dark. Everything that is above absolute zero glows in infrared, so I'm finding it difficult to imagine why APOD included this somewhat unscientific, closing sentence.

[Chris Peterson]

"Some of Io's volcanic lava is so hot it glows in the dark." I picture all lava as glowing in the dark, mainly because lava is red hot molten rock. If something glows, it glows in the light as well as the dark. Everything that is above absolute zero glows in infrared, so I'm finding it difficult to imagine why APOD included this somewhat unscientific, closing sentence.

Your included quote is incomplete. In the caption, it contains a link to a scientific paper that explains just exactly what is meant:

A major and surprising result is that ˜30 of Io's volcanic vents glow in the dark at the short wavelengths of SSI. These are probably due to thermal emission from surfaces hotter than 700 K (with most hotter than 1000 K), well above the temperature of pure sulfur volcanism.

Read the caption in light of RJN's PAGES OF interview and the last sentence makes perfect sense.

[Psnarf]

[Retired University of Arizona employees and/or alumni do not have access to the University Library resources. All I can read is the abstract.]
The full-size image is fascinating. There is not atmosphere, so the only forces on volcanic plumes are the ejection and gravity. Interesting patterns for fluid dynamics study.

(I once drank from a hand-operated water pump in Saratoga Springs, NY. There be sulphur down there! I imagine locals installed the pump because tongues won't freeze onto flagpoles in the summer. There is probably a local cable channel streamed from a hidden camera for their amusement. There may be parimutuel betting involved whether or not tourists can drink an entire cup without a spit-take.)

[neufer]

There is not atmosphere, so the only forces on volcanic plumes are the ejection and gravity.

[b][color=#0000FF]Auroral glows in Io's upper atmosphere. Different colors represent emission from different components of the atmosphere (green comes from emitting sodium, red from emitting oxygen, and blue from emitting volcanic gases like sulfur dioxide). Image taken while Io was in eclipse.[/color][/b]

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[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]

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<<Io has an extremely thin atmosphere consisting mainly of sulfur dioxide (SO₂), with minor constituents including sulfur monoxide (SO), sodium chloride (NaCl), and atomic sulfur and oxygen. The atmosphere has significant variations in density and temperature with time of day, latitude, volcanic activity, and surface frost abundance. The maximum atmospheric pressure on Io ranges from 0.3 to 3 nbar, spatially seen on Io's anti-Jupiter hemisphere and along the equator, and temporally in the early afternoon when the temperature of surface frost peaks. Localized peaks at volcanic plumes have also been seen, with pressures of 5 to 40 nbar. Io's atmospheric pressure is lowest on Io's night side, where the pressure dips to 0.0001 to 0.001 nbar. Io's atmospheric temperature ranges from the temperature of the surface at low altitudes, where sulfur dioxide is in vapor pressure equilibrium with frost on the surface, to 1800 K at higher altitudes where the thinner atmospheric density permits heating from plasma in the Io plasma torus and from Joule heating from the Io flux tube. The low pressure limits the atmosphere's effect on the surface, except for temporarily redistributing sulfur dioxide from frost-rich to frost-poor areas, and to expand the size of plume deposit rings when plume material re-enters the thicker dayside atmosphere. The thin Ionian atmosphere also means any future landing probes sent to investigate Io will not need to be encased in an aeroshell-style heatshield, but instead will require retrorockets for a soft landing.

Gas in Io's atmosphere is stripped by Jupiter's magnetosphere, escaping to either the neutral cloud that surrounds Io, or the Io plasma torus, a ring of ionized particles that shares Io's orbit but co-rotates with the magnetosphere of Jupiter. Approximately one ton of material is removed from the atmosphere every second through this process so that it must be constantly replenished. The most dramatic source of SO₂ are volcanic plumes, which pump 10 tons of sulfur dioxide per second into Io's atmosphere on average, though most of this condenses back onto the surface. Much of the sulfur dioxide in Io's atmosphere sustained by sunlight-driven sublimation of SO₂ frozen on the surface. The day-side atmosphere is largely confined to within 40° of the equator, where the surface is warmest and most active volcanic plumes reside. A sublimation-driven atmosphere is also consistent with observations that Io's atmosphere is densest over the anti-Jupiter hemisphere, where SO₂ frost is most abundant, and is densest when Io is closer to the Sun.>>

[Boomer12k]

Like a peeled Pineapple....


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