Io Overview

1. Io

2. Io Overview • Innermost Galilean Moon • 4th largest moon in the solar system with a diameter of 2,263 miles • Most geologically active object in the solar system “Looking like a giant pizza covered with melted cheese and splotches of tomato and ripe olives, Io is the most volcanically active body in the solar system.” Solarsystem.nasa.gov

3. Io: Technical Information • Orbital period: 1.769 days, rotation is synchronous with orbit • Surface gravity is 1.80 m/s2 • Albedo: 0.62 • Surface temperature: 85K daytime, 140K nighttime (away from hotspots) • Atmospheric Pressure: <10-9 bar Encyclopedia of the solar system: Io the Volcanic Moon

4. Discovery of Io • Discovered on January 8, 1610 by Galileo. • Simon Marius claims he discovered the satellites of Jupiter before Galileo, but Galileo published first so he is credited. • Io was one of Jupiter’s lovers in mythology. http://planetarynames.wr.usgs.gov/Page/Planets#JovianSystem http://galileo.rice.edu/sci/marius.html

5. Discovery of IoEffects on Science • The discovery of moons in orbit around Jupiter became a key piece of evidence for the Copernican view of the universe. • A Danish astronomer, OlausRomer, used observations of the timing of ellipses of Jupiter’s moons to calculate the speed of light. Encyclopedia of the solar system: Io the Volcanic Moon

6. Voyager I • Just a few weeks before Voyager I passed by Io, several scientists made the prediction that Io would have volcanic activity. Voyager I found evidence of this activity as it passed. • Voyager I also measured much higher levels of sulfur in the magnetosphere which had not been detected by the earlier Pioneer 10 and 11 which passed Io in December 1973 and December 1974. Encyclopedia of the solar system: Io the Volcanic Moon

7. Voyager II • Voyager II did not pass as closely to Io as Voyager I. • In the 4 months since Voyager I, a change in volcanic activity was noted. • 7 of the 9 volcanoes imaged by Voyager I were shown to still be active. • Pele, an active volcano imaged by Voyager I was seen to be inactive at the time that Voyager II passed. http://voyager.jpl.nasa.gov/gallery/images/jupiter/io.gif

8. Tidal Heating • Laplace discovered a relationship between the orbits of Io, Europa, and Ganymede in 1805. This relationship is called Laplace Resonance. • The satellites’ orbits have a 4:2:1 ratio. Meaning for each time Io orbits Jupiter, Europa only orbits ½ way and Ganymede orbits only ¼ way. http://en.wikipedia.org/wiki/File:Galilean_moon_Laplace_resonance_animation.gif • This forces Io’s orbit into an oval shape: Io is closer to Jupiter during some parts of the orbit than others. • This, combined with the gravitational pull from Europa and Ganymede, causes Io to deform and relax multiple times during its orbit. • As it gets closer to Jupiter it deforms toward Jupiter and relaxes as it moves further away and the gravitation pull of its neighboring moons gets stronger. • This pattern causes Io’s interior to heat up in the same way that repetitive bending of a wire hanger would eventually cause the wire to heat up. Encyclopedia of the solar system: Io the Volcanic Moon http://nasa.gov/topics/solarsystem/features/io-volcanoes-displaced.html

9. Tidal Heating • Tidal heating is a much stronger heating mechanism than internal heating (by 200x) and is responsible for Io’s hyperactivity. • The interior temperature is due to an equilibrium between tidal heating and heat transfer from Io to the surrounding space. • The heat transfer on Io is driven by melt segregation. This is the process of molten rock flowing to the surface and burying older, solidified flows. This leads to a constantly renewed surface. http://www.nasa.gov/topics/solarsystem/features/io-volcanoes-displaced.html Encyclopedia of the solar system: Io the Volcanic Moon http://photojournal.jpl.nasa.gov/jpegMod/PIA02501_modest.jpg Williams, David A.; Howell, Robert R.; Active Volcanism: Effusive eruptions

10. Surface Characteristics • Io has a metallic core and a silicate mantle. • There is some sort of differentiated crust, but its composition is unknown. • Io has at least 166 active volcanic landforms interspersed among sulfurous frost deposits. • The many colors of the surface are due to sulfur deposits in many stages of cooling. • There are mountains of volcanic and tectonic origin. • Scarps cross the moon as well. • Some are parallel and appear to be tectonic in nature. • Others are jagged and seem to be the result of erosion. • There is not enough atmosphere or liquid on the surface of Io for traditional erosion. Sulfur and sulfur dioxide escaping from subterranean reservoirs has been suggested as the source of the erosive material. Encyclopedia of the solar system: Io the Volcanic Moon

11. Volcanoes On Io • Two volcanoes represent the different types of activity seen on Io: • Pele: eruption times on the scale of days or weeks, plume heights of approximately 300km, temperatures of 650 K and dark deposits • Prometheus: year long eruptions, plume heights 60-100km, ring deposits http://www.nasa.gov/topics/solarsystem/features/io-volcanoes-displaced.html Williams, David A.; Howell, Robert R.; Active volcanism: Effusive eruptions

12. Other Recognizable Features • Loki Patera is a huge lava lake that is very recognizable. It is sometimes the brightest hot spot on Io. • There have been recurring “brightenings” • observed in the area around Loki. • This phenomena has not been explained • but was observed by Galileo and • confirmed by ground based • observations. • In many images of Io, Loki • appears as a dark horseshoe. Encyclopedia of the solar system: Io the Volcanic Moon

13. Atmosphere • Io’s atmosphere has very low density which consists mainly of sulfur dioxide. • Sulfur dioxide is largely emitted by volcanic plumes. • Some is also evaporated from the sulfurous frost deposits. • Io’s low gravity permits this sulfur dioxide to escape and it dissociates into sulfur and oxygen neutrals. • These neutral particles become a part of the aurora and further afield, the plasma torus. • In the aurora, green is sodium atoms, red is oxygen and blue is sulfur. This is the only evidence thus far for the presence of sodium on Io. • The blue regions of the aurora could also be correlated to the flux tube between Io and Jupiter. The flux tube allows the exchange of charged particles between the two bodies. Encyclopedia of the solar system: Io the Volcanic Moon

14. Plasma Torus • Donut shaped trail of charged sulfur and oxygen particles that follows Io in its orbit. • Formed from the sulfurous emissions from the moons volcanic activity. • UV radiation from the sun bombards ions of the gases such as sulfur dioxide resulting in a cloud of ions and electrons. • These ions and electrons then move with Jupiter’s magnetic field in the same orbit as Io. • There is evidence that the plasma torus has large impacts on Jupiter’s magnetic field. • This effect could be correlated with levels of volcanic activity which may change the density and composition of the plasma torus periodically. Encyclopedia of the solar system: Io the Volcanic Moon http//:vega.lpl.arizona.edu/iotorus/

15. Questions that Remain • What is the composition of the crust? What type of magma is emitted from the volcanic landforms? Is sulfur dioxide the only volatile present in the magma? • What is the exact nature of the tidal heating? • Volcanic eruptions take place away from where scientific models would predict. • This could be due to faster than calculated rotation of Io, the ability of magma to travel far distances beneath the surface, or inadequacies in the tidal heating model which neglect a crucial unknown component. • Galileo only managed to study the side of Io facing away from Jupiter. What is the behavior of the Jupiter facing side? Are there active landforms that could provide more insight into the nature of Io’s interior? • What is the exact nature of the flux tube? What is the composition of the particles and where do they com from? Encyclopedia of the solar system: Io the Volcanic Moon http://nasa.gov/topics/solarsystem/features/io-volcanoes-displaced.html

16. Future Missions? • There are currently no missions planned to Io. • A mission to Jupiter named Juno is currently planned and this could provide information about the interaction between the two bodies but Juno will not carry technology useful for observing Io itself. • Planning of future missions is on hold, awaiting development of more radiation robust technology. Marchis, Franck; Spencer, John R.; Lopes, Rosaly M. C.; Outstanding Questions and future explorations

17. Comparison of Voyager and Galileo Images http://nssdc.gsfc.nasa.gov/image/planetary/jupiter/gal_io2_47972.jpg