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[edit] Mercury

[edit] Venus

[edit] Earth

[edit] Mars

[edit] Jupiter

Jupiter currently has 63 discovered satellites, but the 4 Galilean Moons (Io, Callisto, Europa, and Ganymede) are the largest.

[edit] Io

[edit] Discovery/History

Wikimedia Commons True Color Image

Io has had a long history since its discovery in 1610 by Galileo Galilei. Telescope technology limited observations of Io until the late 1800s when large scale features were able to be resolved on its surface^[1]. Observations show that Io has areas of red, brown, orange, and yellow which were later attributed to the abundance of sulfur and sodium on the surface and the unusually high amount of volcanic activity. Io is the most volcanically active body in the solar system. Its activity is due to a great deal of tidal heating from Jupiter and a resonant orbit with Jupiter’s other moons.

[edit] Origin of Internal Energy

Io has a similar density to our moon, but is made mostly of sulfur compounds^[2]. Io experiences a large amount of tidal heating because it orbits Jupiter at a relatively close distance of 422,000km and gravitational interactions with other Galilean moons. Jupiter’s large gravitational field and Io’s interactions with other satellites have resulted in an orbital resonance between Io, Europa, and Ganymede which means their orbital periods are integer multiples of each other^[3].

Wikimedia Commons Io Eruption Plume Image

For each orbit of Ganymede, Europa orbits twice and Io orbits four times, this forces Io to have a more eccentric orbit. The eccentric orbit means that Io's orbital distance continuously varies, which causes expansion and contraction of its tidal bulge. This frictional energy is dissipated in the form of heat. Io’s internal heat melts the sulfur-rich core into liquid magma, which is contained in large subsurface chambers^[4]. This process raises the internal pressure of Io and causes volcanic activity. It is believed that Io has a thin rigid lithosphere and a constant flowing liquid mantle due to its constant internal heating. It is estimated that the power dissipation from tidal interaction is two orders of magnitude greater than radioactive decay. For this reason, Io has a maximum observed temperature of ~1800K- the second highest in the solar system^[4]. Another manifestation of the large power dissipation is a large heat flow, 30 times larger than found in Earth’s volcanoes.

[edit] Volcanic Features

It is not surprising that Io’s surface is dominated by volcanic features. The surface is littered with pit craters, calderas (volcanic craters), lava flows, shield volcanoes, ash plains, sulfur (S) deposits and other features.

Wikipedia Image of Active lava flows in the Tvashtar Paterae region. Images taken by Galileo in 1999 and 2000

There are over 500 volcanoes on the surface of Io. There are also over 200 calderas, some of which stretch up to 200km across; these calderas are surrounded by different patterns such as bright rings from condensing sulfur ejecta^[3]. Volcanic eruptions cause these plumes of ejecta, which can be sprayed up to a height of 300km and 1000km in diameter^[2]. The formation of the ejecta plumes is determined by the type of eruption and the characteristics of the material ejected (i.e. molecular composition or phase of matter). Large lava flows are common on the surface due to large volcanic plume velocities of ~1km/s. Lava flows create intervent planes which are areas between volcanoes where lava flows are frequently resurfacing, keeping them flat^[5]. Unlike the Earth, there has been no evidence shown that Io has plate tectonics; there are also anomalous isolated mountains in the polar regions^[3].

[edit] Plasma Torus

Recently, it has been discovered that Io has a plasma torus. The plasma torus is created by the volcanoes that eject sodium and sulfur gas and plasma into Io’s atmosphere. Since Io is not very massive it is not able to hold a substantial atmosphere, leaving behind a “tail” which follows Io’s orbit around Jupiter. Jupiter’s magnetic field strips off more than 1000kg of Io's material per second^[6]. The plasma torus is held in place by Jupiter’s large magnetic field, which causes the charged particles (protons and electrons) in the field to orbit a center of rotation, which causes these particles to stay in a relatively small area. Some of these ions are drawn towards Jupiter’s atmosphere by its magnetic field lines, when these ions interact with Jupiter’s atmosphere, auroras are created. The excess stripped ions in the torus double the size of Jupiter’s magnetosphere compared with theoretical calculations^[6]. Spectral observations show that Io’s torus and ionosphere are depleted by processes that produce a large nebula expanding out to ~500 Jupiter radii^[7]. One of the latest methods of studying the plasma torus is with high resolution (R~120000) spectra of neutral oxygen emissions (630nm) as well as other emissions with the Wisconsin H-Alpha Mapper (WHAM) instrument in Madison, Wisconsin. These observations have shown that emissions show significant long and short-term variations of oxygen emissions. Since intensity variations exist along with a long-term intensity average, it has been concluded that the emissions cause an interaction between Io’s torus and its atmosphere^[8]. The reason for studying emissions is to measure the composition as well as velocity structures. This spectra is being taken with a dual Fabry-Perot etalon system to filter out the multiple orders that are produced by etalons^[9].

[edit] Io's Surface and Subsurface

Wikimedia Commons Io Interior Image

Research is also being directed towards Io’s surface and subsurface processes. Scientists are currently trying to map the anti-Jovian hemisphere as well as analyze volcanic, tectonic, and other processes affecting the region^[10]. Observations show that Io’s entire surface is constantly changing because of subsurface processes, but most eruptions are found to be confined to isolated areas. Volcanic events only take place on about 17% of the surface which points back to the large lava flows that can extend up to 1000km^[10]. Similar to Earth’s geysers, Io’s fissures release gases and liquids like sulfur vapor up to 225km and can last for days. Io’s surface has been found to be very active and volatile; it has been observed that changes in volcanic spray were detected in a 5.5 hour period. A New Frontiers class mission named Argus is a planned mission to send a spacecraft to Io that would orbit the moon 40 times at about 100km altitude. The goal of the mission is to attempt to answer basic questions about the possible habitation of planetary bodies like Europa and Enceladus, which are both under the influence of significant tidal heating^[11].

[edit] Saturn

[edit] Uranus

[edit] Neptune

[edit] References