Galilean satellites

The four largest satellites of Jupiter, lo, Europa, Ganymede and Callisto can be seen using a binocular. In 1609, Galilei was the first to observe them through a telescope. Because of their orbital motions, they appear in the equatorial plane east and west of Jupiter. Some important physical parameters of the Galilean Satellites are given in Table 4.1. 

In Europe, there is a study (HADES) for a satellite mission to Europa (orbiter, lander, cryobot) (Bottcher et at., 2009 [39]). 

It was a big surprise when on lo active volcanism was detected on its surface (see Eig. 4.1). On Earth, the heat source that produces volcanic activity comes from its interior where radioactive materials decay and release energy and also from heat left over from its formation, accretion heat. This however cannot explain the volcanism on lo. The satellite is too small and should have cooled out. The only mechanism to maintain active volcanism on lo is tidal heating (see also Moore, 2003 [236]). The semi major axis of the orbit of lo is 421800 km so it is close to Jupiter and exposed to strong tidal forces. One revolution around Jupiter takes only 1 d 18 h 27 min. The albedo of lo is 0.61 which is a relatively high value. Other parameters 

Hanslmeier, Water in the Universe, Astrophysics and Space Science Library 368, DOI 10.1007/978-90-481-9984-6 4, Springer Science+Business Media B.V. 2011 

Satellite Diameter km Mass kg Density g/cm Semi-major axis km 

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The committee surveyed the inventory of environments in the solar system and asked which non-Earth ones might be suited to fife of the terran type. Such locales are few, unless there are laws not now understood that could govern the early stages of the self-organization of biochemical structures and processes that could lead inevitably to evolving life forms.15 Subsurface Mars and the putative sub-ice oceans of the Galilean satellites are the only locales in the solar system (other than Earth itself) that are clearly compatible with terran biochemistry. 

Figure 1 Spectral geometric albedo (1.0 = white disk of same radius) of the Galilean satellites. Hemispheric average values from telescopic observations (after Clark and McCord, 1980a).

The Galilean satellites of Jupiter, discovered in 1610 by Galileo, are the most easily observed outer planet satellites because of their size and relative proximity to the Earth. Eigure 1 shows the hemispheric-scale telescopic spectra of the satellites (Clark and McCord, 1980a). Immediately... 

Figure 6 Examples of Galileo NIMS speetra from iee-rich (thin lines) and ice-poor (thick lines) regions from the three icy Galilean satellites. The ice-poor regions are interpreted as containing mixtures of water ice with darker hydrated minerals (Callisto and Ganymede) and heavily hydrated salts (Europa and Ganymede) (after McCord et al, 1999) (reproduced by permission of American Geophysical Union from J. Geophys. Res. Planets 1999, 104, 11827-11851).

Finally, ammonia and methane have both been proposed as minor constituents of the Galilean satellites in hydrated or clathrated form, possibly lowering the melting point in their interiors and promoting ice (or cryo-) volcanism (Hogenboom etal., 1997 Kargel, 1992 Lewis, 1973). However, as of the early 2000s, there has been no identification of these materials on the satellite surfaces. 

This survey of the current state of knowledge of satellite geochemistry also uncovers the many areas where there are unsolved problems and major issues still to be addressed by future observations and theoretical work. On the observational side, most of the chemical information we now have for objects beyond the Galilean satellites comes from bulk density and global telescopic spectral data. The Cassini/Huygens mission, which arrives at Saturn in July of 2004, will allow more detailed study of all the satellites of this major system. In particular. Titan is now known primarily through detailed study of its upper atmosphere from Voyager and Earth-based... 

Nelson R. M., Lane A. L., Matson D. L., Veeder G. J., Buratti B. J., and Tedesco E. F. (1987) Spectral geometric Albedos of the Galilean satellites from 0.24 to 0.34 micrometers— observations with the international ultraviolet explorer. Icarus 72, 358-380. 

Neubauer F. M. (1998) The sub-Alfvenic interaction of the Galilean satellites with the Jovian magnetosphere. J. Geophys. Res. Planets 103, 19843-19866. 

Pilcher C. B., Ridgway S. T., and McCord T. B. (1972) Galilean satellites—identification of water frost. Science 178, 1087-1089. 

Pollack J. B. and Reynolds R. T. (1974) Implications of Jupiter s early contraction history for composition of Galilean satellites. Icarus 21, 248-253. 

Spencer J. R., Calvin W. M., and Person M. J. (1995) Charge-coupled-device spectra of the Galilean satellites—molecular-oxygen on Ganymede. J. Geophys. Res. Planets 100, 19049-19056. 

Io is the innermost of the four Galilean satellites and the most dense of the Jovian moons. Its density is estimated at 3.5 g/cm3. In some ways, its size, structure, and chemical composition are similar to those of our Earth s Moon. As the illustration shows, Io probably has the largest core for its size of any of the four moons. Io s surface is unusually smooth, essentially lacking in any impact craters. This evidence suggests that the moon s surface is fairly new, probably no more than about a million years old. 

Greenberg, R. (19..) Galilean satellites Evolutionary paths in deep resonance. Icarus 70, 334-347. 

Gravitational N-body dynamical systems usually have only the current positions and velocities of the bodies as the observational evidence of their past history. The traces of their past behavior exist only as conceptual, theoretically computed orbits. However, the Laplace orbital resonance among the galilean satellites actually leaves a visible record of its behavior in a surprising and seemingly unlikely form Linear traces in distinctive geometric patterns clearly visible on the surface of the satellite Europa are a direct recording of the effect of the orbital resonance. 

Figure 1. A Voyager image of a far southern region on Europa, showing many distinctive cycloidal ridges, which mark the paths of cracks in Europa s crust. These linear trajectories are the result of the Laplace orbital resonance among the Galilean satellites. Three of the Cycloids have IAU assigned names, as shown. Cycloids are chains of arcs, each typically 100 km long, often with a dozen or so arcs in each chain.

Another interesting feature of Europa s light scattering near opposition is the double-minima shape of the negative polarization branch (see Figure 13). This effect recently was seen in telescopic observations of Galilean satellites and some bright asteroids [29,30,36]. 

The four largest satellites of Jupiter - Ganymede, Callisto, lo, and Europa - are known as the Galilean satellites after their discovery by Galileo in 1610. Ganymede is the largest natural satellite in the solar system and is in tact larger than Mercury it is followed by Titan (Saturn), Callisto (Jupiter), lo (Jupiter), the moon (earth), Europa (Jupiter), and Triton (Neptune). 

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