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The Io Plasma Torus (IPT) is a doughnut-shaped structure of charged particles, composed mainly of sulfur and oxygen ions. The main source of the IPT is the moon Io, the most volcanically active object in the Solar System. Io is the innermost of the Galilean moons of Jupiter, the main source of the magnetospheric plasma and responsible for injecting nearly 1 ton/s of ions into Jupiter's magnetosphere. In this work ground-based observations of the [SII] 6731 Å emission lines are observed, obtained at the MacMath-Pierce Solar Telescope. The results shown here were obtained in late 1997 and occurred shortly after a period of important eruptions observed by the Galileo mission (1996-2003). Several outbursts were observed and periods of intense volcanic activity are important to correlate with periods of brightness enhancements observed at the IPT. The time of response between an eruption and enhancement at IPT is still not well understood.

We base our search for the right instrumentation for detecting biosignatures on Europa on the analogy suggested by the recent work on polar ecosystems in the Canadian Arctic at Ellesmere Island. In that location sulphur patches (analogous to the Europan patches) are accumulating on glacial ice lying over saline springs rich in sulphate and sulphide. Their work reinforces earlier analogies in Antarctic ecosystems that are appropriate models for possible habitats that will be explored by the European Space Agency JUpiter ICy Moons Explorer (JUICE) mission to the Jovian System. Its Jupiter Ganymede Orbiter (JGO) will include orbits around Europa and Ganymede. The Galileo orbital mission discovered surficial patches of non-ice elements on Europa that were widespread and, in some cases possibly endogenous. This suggests the possibility that the observed chemical elements in the exoatmosphere may be from the subsurface ocean. Spatial resolution calculations of Cassidy and co-workers are available, suggesting that the atmospheric S content can be mapped by a neutral mass spectrometer, now included among the selected JUICE instruments. In some cases, large S-fractionations are due to microbial reduction and disproportionation (although sometimes providing a test for ecosystem fingerprints, even though with Sim – Bosak – Ono we maintain that microbial sulphate reduction large sulphur isotope fractionation does not require disproportionation. We address the question of the possible role of oxygen in the Europan ocean. Instrument issues are discussed for measuring stable S-isotope fractionations up to the known limits in natural populations of δ34 ≈ −70‰. We state the hypothesis of a Europa anaerobic oceanic population of sulphate reducers and disproportionators that would have the effect of fractionating the sulphate that reaches the low-albedo surficial regions. This hypothesis is compatible with the time-honoured expectation of Kaplan and co-workers (going back to the 1960s) that the distribution range of 32S/34S in analysed extra-terrestrial material appears to be narrower than the isotopic ratio of H, C or N and may be the most reliable for estimating biological effects. In addition, we discuss the necessary instruments that can test our biogenic hypothesis. First of all we hasten to clarify that the last-generation miniaturized mass spectrometer we discuss in the present paper are capable of reaching the required accuracy of ‰ for the all-important measurements with JGO of the thin atmospheres of the icy satellites. To implement the measurements, we single out miniature laser ablation time-of-flight mass spectrometers that are ideal for the forthcoming JUICE probing of the exoatmospheres, ionospheres and, indirectly, surficial low-albedo regions. Ganymede's surface, besides having ancient dark terrains covering about one-third of the total surface, has bright terrains of more recent origin, possibly due to some internal processes, not excluding biological ones. The geochemical test could identify bioindicators on Europa and exclude them on its large neighbour by probing relatively recent bright terrains on Ganymede's Polar Regions.

Jupiter's moons, embedded in the magnetized, flowing plasma of Jupiter's magnetosphere, the plasma seas of the title, are fluids whose highly non-linear interactions imply complex behavior. In a plasma, magnetic fields couple widely separated regions; consequently plasma interactions are exceptionally sensitive to boundary conditions (often ill-specified). Perturbation fields arising from plasma currents greatly limit our ability to establish more than the dominant internal magnetic field of a moon. With a focus on Ganymede and a nod to Io, this paper discusses the complexity of plasma-moon interactions, explains how computer simulations have helped characterize the system and presents improved fits to Ganymede's internal field.

Keldysh Institute of Applied Mathematics, Russiaemail: korab@iki.rssi.ruAbstract.An international effort dedicated to science exploration of Jupiter system plannedby ESA and NASA in the beginning of next decade includes in-depth science investigation ofEuropa. In parallel to EJSM (Europa-Jupiter System Mission) Russian Space Agency and theacademy of Science plan Laplace-Europa Lander mission, which will include the small telecom-munication and scienceorbiter and the surface element: Europa Lander. In-situ methods on thelander provide the only direct possibility to assess environmental conditions, and to performthe search for signatures of life. A critical advantage of such in situ analysis is the possibilityto enhance concentration and detection limits and to provide ground truth for orbital measure-ments. The science mission of the lander is biological, geophysical, chemical, and environmentalcharacterizations of the Europa surface. Remote investigations from the orbit around Europawould not be sufficient to address fully the astrobiology, geodesy, and geology goals. The scienceobjectives of the planned mission, the synergy between the Europa Lander and EJSM missionelements, and a brief description of the Laplace-Europa Lander mission are presented.Keywords.Europa; Jupiter; Galilean satellites; habitability; space research.

Four hundred years ago Galileo turned his telescope to the heavens and changed the way we view the cosmos forever. Among his discoveries in January of 1610 were four new ‘stars’, following Jupiter in the sky but changing their positions with respect to the giant planet every night. Galileo showed that these ‘Medicean stars’, as he named them, were moons orbiting Jupiter in the same manner that the Earth and planets revolve about the Sun in the Copernican theory of the solar system. Over the next three centuries these moons, now collectively named the Galilean satellites after their discoverer, remained tiny dots of light in astronomers' telescopes. In the latter portion of the twentieth century Galileo's new worlds became important targets of exploration by robotic spacecraft. This paper reviews the history of this exploration through the discoveries made by the Galileo mission from 1995 to 2003, setting the stage for on-going exploration in the new century.

In the spirit of the symposium and the theme of the session of this presentation, “Our solar system after Galileo, the grand vision,” I review briefly a relatively recently discovered phenomenon in the solar system – existence of atmospheres on certain moons, including Io, one of the four moons Galileo discovered four centuries ago. The origin of such atmospheres is discussed, and comparisons are made between various gassy moons.

As most of the natural satellites of the Solar System, the Galilean moons are since a long time assumed to be tidally locked in a spin-orbit synchronous resonance. Thanks to the mission Galileo, we now dispose of enough gravity data to perform 3-dimensional theories of the rotation of these satellites, in particular to model the departure from the exact synchronous rotation. We here present such theories depending on the interior model we consider, in highlighting some observable output data. Inverting them will give us information on the internal structure of these bodies.

Galileo's imagination was quick to comprehend the importance of the 4 starry objects he observed near Jupiter in January 1610, not only for himself as a scientist but for our common understanding of the place of the Earth and our species in the cosmos. Even he, however, could not have imagined what those four objects would actually look like once humans got their first good look. Some 369 years the fast traveling Voyager 1 and 2 spacecraft provided that first good look during 1979, followed by an even closer look from the Galileo Orbiter beginning in 1996 through 2001. The following mosaics represent some of the best of those views. They include views of impact craters young and ancient, icy terrains that have been intensely faulted, eroded or disrupted, mountains towering 10 or more kilometers high, and volcanic eruptions hotter than those on Earth. Each of the four Galilean satellites is geologically distinct, betraying very diverse global histories and evolutions. Images and other observations of these 4 objects revealed the importance of tidal heating and subsurface water oceans in planetary evolution, but mapping is very incomplete. New missions to explore these planetary bodies are being planned and the images and observations of the missions that went before will lay the groundwork for these new explorations as we begin the 5th Galilean century.

Galileo realized that the four moons he discovered, besides supporting the heliocentric system, could also serve as a clock in the sky for longitude determination. Navigation at sea by this method did not prove practical but G. Cassini used it to improve land mapping. O. Rømer discovered that the interval between eclipses of the moons by Jupiter increased or decreased according to whether the Earth moved away from or toward Jupiter. He attributed this to the finite speed of light which he in 1676 determined with an error of about 25%. Timings of the eclipses by Jupiter have served to compute accurate orbits of the moons, notably by means of R. A. Sampson's theory of 1921. Beginning in 1973, light curves of mutual eclipses and occultations between pairs of moons have been made regularly at six years intervals. From these observations very accurate radii and positions of the moons have been obtained.

Observational astronomy began in Padova four hunderd years ago, when Galileo Galilei pointed a newly invented instrument towards Jupiter. After only one week of observations he discovered four moons circling Jupiter. In the intervening four centuries, technical progress in instrumentation and novel observational approaches have revealed much about the connection between these Medicean moons with Jupiter, none more revealing than the auroral emissions. In this paper we review observations of ultraviolet aurora made by earth-orbitting spacecraft as well as those that flew by the Jovian system . Four hundred years ago today, observations of the night sky from this historic town revolutionized science. On this day, Galileo Galilee built his version of a toy invented by opticians, pointed it at the heavens and discovered four previously unknown moons orbiting Jupiter. This was truly a triumph of technology as these objects lied beyond the reach of the best observational tools available at the best observatories of the time. In an early demonstration of faster, better, cheaper, a scientific instrument that was shorter than a typical walking stick and took only weeks from the decision to develop to science results, established its superiority over naked-eye, castle-like observatories, that was the custom of the day. Since that auspicious day, creative minds have developed various telescopes and tools that have revealed many unexpected phenomena and surprising characteristics including those that are truly invisible to the human eye. Four centuries of advances in technology have allowed us to answer many of the original questions on these Medicean moons. Our instruments on remote mountain tops, on space platforms near Earth, as well as those that have orbited Jupiter and flew past the Jovian system have given us a closer look of these bright points of lights. We now have a fairly good understanding of the major physical attributes of these moons, know how different they are from our own and from each other and why. In this paper we will review observational progress made in our understanding of Jupiter and the Galilean moons and their magnetic connections as revealed through au- rora. Auroral emissions and their morphology contain information on atmospheric compo- sition, plasma interactions, magnetic field configuration, and magnetosphere-ionosphere coupling processes. Jupiter and its moons provide us with a rich wall-less laboratory envi- ronment that is accessible to probing by our spaceborne and ground-based observatories. This is a chronicle of the triumph of technology. In the past two decades, new instru- ments behind large telescope have obtained conclusive evidence of planets around distant

We present preliminary results for our study of mutual phenomena of the Galilean satellites performed at radio wavelengths with the Medicina and Noto antennas of the Istituto di Radioastronomia - INAF, and with the Effelsberg 100-m radio telescope of the Max-Planck-Institute for Radioastronomy, Bonn. Measurements of the radio flux density variation during the mutual occultations of Io by Europa and Ganymede were carried out during the PHEMU09 campaign at 22 GHz and 43 GHz. Flux density variations observed at radio wavelengths are consistent with the typical optical patterns measured when partial occultations occur.

Terrestrial planets in close orbits around magnetic white dwarf stars can be electron-cyclotron maser sources, by analogy to planetary radio emissions generated from the electrodynamic interaction between Jupiter and the Galilean moons. We present predictions of the radio flux densities from white-dwarf/terrestrial-planet systems and discuss a scenario for the formation of these systems.

Analysis of data from the Galileo spacecraft continues to provide significant advances in our understanding of the geology and composition of Jupiter’s icy Galilean satellites Callisto, Ganymede, and Europa.

New constants for Sampson-Lieske theory of the Galilean Satellites have been derived using 6360 individual photographic positions (1891–1990) and 438 pseudo astrometric positions from mutual occultations during 1973, 1979, 1985 and 1991. Using these new sets of constants, significant improvement is noticed in the O-C values of the sky plane coordinates of the mutual event data set and residuals in longitude for Io and Europa are found to improve. Problems concerning the inclusion of mutual event data in attempting evaluation of secular variations of the mean motions of the satellites are discussed.

Photographic observations of the Galilean satellites of Jupiter have been made in Pulkovo with 26-inch refractor during two periods 1976–1981 and 1986–1993. The internal mean square errors of jovicentric coordinates and mutual distances is equal to 0.10 arcsec. The external errors are equal to 0.08 and 0.17 arcsec in AR and Decl. The systematic errors were analysed. The errors of the theory G-5 of J.E. Arlot do not exceed 0.1 arcsec.

For improved establishment of the dynamical reference frame and tying it to the stellar reference frame, a method to observe close approach (CA) events between satellite and satellite and/or satellite and star is proposed here. The accuracy of measurements of angular distance is 0”.02 – 0”.03 for a single data point. We apply this technique fairly successfully to the CA events of the Galilean satellites and a preliminary orbital longitude correction to the E2X3 constants of J4 is obtained from eight CA observations ranging from 1987 to 1989.

UVS results from Jupiter show the Io torus colder and brighter than the Voyager observations. Aurora near Jupiter’s poles emit 1-4 MR from altitudes of 300 – 400 km. Ganymede and Callisto have extended hydrogen exospheres. The near-UV reflectance of the Galilean satellites shows SO2, magnetospheric alteration, and O3. Remote sensing of Jupiter’s stratospheric haze determines that it thickens and darkens towards higher latitudes.

In order to determine precisely positions of the Galilean satellites of Jupiter, it is useful that shortly before and/or after photometric observations of a mutual event, normal CCD imaging observation is also performed for the two small-separation satellites. Experimental observations showed that the two observational types, on the whole, could derive mean (O-C) s with very good internal and external agreement (about 15–20 mas).

It was with a mixture of incredulity and excitement that I heard on the BBC radio morning news that the NASA Voyager 1 mission had observed active, explosive volcanism on Io, one of the four Galilean satellites orbiting Jupiter. This was March 1979 and at that time we had seen no evidence of recent volcanic activity anywhere else in the Solar System other than Earth. It should not have been a surprise. That Io, a Moon-sized planetary body, could be volcanically active had been predicted by a California-based team and their work was published a few days before Voyager returned the now-famous …

One of the premier areas of scientific return from Hubble Space Telescope (HST) observations of Solar System objects has been studies of the Galilean satellites of Jupiter. Because these objects are unresolvable in most ground-based observations, HST’s spatially resolved imaging and spectroscopy of their surfaces, atmospheres, and electrodynamic interactions with the Jovian magnetosphere have provided unique results. This talk will review highlights of the science results from HST observations of the Galilean satellites, including discovery of auroral emissions at the poles of Ganymede, the recent discovery of molecular sulfur in the Pele plume on Io, and the presence of SO2 in the surface of Callisto.

In this communication the main equations for the variables: radius vector, longitude, P and Q (variables built from Laplace's perihelium first integral) are given in closed form. These equations are used for deriving the equations of a second-order theory. At this order, the equations for P and Q, are separated and they are integrodifferential linear equations. The equations for the radius vector and for the longitudes, give, after integration, perturbations which are purely trigonometric. The solution shows the features observed in the motion of Jupiter's Galilean satellites. The results are discussed, and extended to include the space variables.

Ground-based and spacecraft observations of planets, satellites, and asteroids in the thermal infrared have provided a wealth of information on planetary temperatures, dimensions, and surface properties. Internal heat sources have been revealed for Jupiter, Saturn, and Neptune, and active volcanism on Io has been discovered and monitored. The thermophysical properties of Mars have been mapped for nearly all the surface by spacecraft, and ground-based observations have given similar information for the Galilean satellites of Jupiter. Infrared radiometry thus sheds important light on significant problems of dynamics, interiors, and surfaces of solar system bodies.

Several aspects of space glaciology are considered in the paper. Estimates of the water content of the Earth, Mars, and the Galilean moons of Jupiter are corrected. A considerable proportion of the total amount of water in the solar system is localized near Jupiter; part of this water is contained as ice in glaciations, glacial caps, and ice crust on the planets. Ice is one of the main components of the surface of some planets. The major amount of ice on Mars is contained in a permafrost layer of mean thickness about 3 km. The model of an ice crust floating on a water mantle is considered for Jupiter’s moon Europa. It is shown that for definite values of certain parameters this crust may be subject to destruction due to the instability of its proper oscillations, which explains the numerous systems of fractures and cracks observed on Europa’s surface. The stress-strain state of such an ice crust is calculated within the framework of a non-linear thermo-elasticity model. The role of short-period temperature variations at Europa’s surface is estimated and the peculiarities of relief observed on this planet are analysed.

Observations of the minute disks of Uranus and Neptune from the surface of the earth present a major challenge to any observatory site and require the most advanced techniques in optical imaging instrumentation. Less than 4 arcsec across, the disk of Uranus would fit within the Great Red Spot of Jupiter in the focal plane of a terrestrial telescope; the smaller disk of Neptune, less than 2.5 arcsec in diameter, is scarcely more than half again that of Ganymede, the largest of the Galilean satellites. At present, both planets are situated at far southerly declinations, making them even more difficult objects for Northern Hemisphere observatories.

The capture of satellites is considered to be a slow process, in which particles approaching the planet lose their energy gradually and fall down into the stable orbits around it. Therefore, in order to investigate the capture problem, it seems to be necessary to clarify the behaviors of orbits near the planet. Recently Hayashi et al. (1977) and Heppenheimer and Porco (1977) found that in the restricted three body problem, particles incident through Lagrange points L1 and L2 revolve always directly around Jupiter as long as the potential windows at L1 and L2 are small. This suggests the impossibility of the capture of retrograde satellites when the potential windows are small.

Most of the natural satellites of the planets of the solar system may be put into one of three main groups, according as to which of three main influences dominate the perturbation of their motion from Keplerian motion about the primary planet. The first of these is the attraction of the Sun, which governs the perturbations of the Moon's motion about the Earth, and those of the outer satellites of Jupiter (satellites VI to XIII), and Saturn's satellite Phoebe. The second is the departure of the gravitational field of the planet from that of a spherically symmetric body (the “figure terms”), and this governs the perturbations of the two satellites of Mars, Jupiter's satellite Amalthea (V), Neptune's satellite Triton, is probably the most important influence on Uranus' satellites, and is important, though not dominant, for the inner satellites of Saturn. The third influence is the mutual attraction of the satellites themselves. An order of magnitude argument suggests that periodic perturbations from this cause could scarcely be expected to be measureable from Earth, were it not that the frequent appearance of small-integer near-commensurabilities of pairs of orbital periods, and the consequent argumentation of the associated perturbations by a variety of types of resonance effects, in the systems of Jupiter and Saturn, causes mutual perturbations to dominate the orbital theories of three of the four great satellites of Jupiter, and six of the nine satellites of Saturn, and enables the masses of most of the satellites involved to be determined with otherwise unexpected relative precision (in some favourable cases, of the order of one per-cent) from Earth based data. Let us now consider the satellite systems of each of the outer planets in a little more detail.

It is well known that the satellite systems of the major planets Jupiter, Saturn and Uranus share many of the same regular features that can be seen in the planetary system of the Sun. The inner satellite orbits are nearly circular and lie in the plane defined by the axis of rotation of the central body. Again the distances Rn of the regular satellites, numbered inwards to the centre n = 0, 1, 2, …, form a nearly geometric sequenceRn/Rn + 1 ≌ constant,similar to the Titius-Bode law of planetary distances. These facts suggest that the same cosmogonic process must have been responsible for the origin of both types of systems.

Some of the Galilean satellites show evidence of two distinct surface types, a high albedo frost and a dark, presumably silicate material. We are beginning a program to map the spatial distribution of these components with a Michel son spatial interferometer. This will be done both in and next to the 2.0µm frost absorption band. While the mapping program is just beginning, this investigation has already yielded new information on the wavelength dependence of seeing in the infrared.