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.

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.

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.

The ability to differentiate abiotic organic material from material of a biological origin is a critical task for astrobiology. Mass spectrometry and spectroscopy provide key tools for advancing this task and are two techniques that provide useful and highly complementary compositional information independent of a specific biochemical pathway. Here we address some of the utility and limitations of applying these techniques to both orbital and in situ exploration of icy moons of the outer solar system.

Galileo spacecraft data suggest that a global ocean exists beneath the frozen ice surface Jupiter's moon Europa. Since the early 1970s, planetary scientists have used theoretical and observational arguments to deliberate the existence of an ocean within Europa and other large icy satellites. Galileo magnetometry data indicates an induced magnetic field at Europa, implying a salt water ocean. A paucity of large craters argues for a surface on average only ~40-90 Myr old. Two multi-ring structures suggest that impacts punched through an ice shell ~20 km thick. Europa's ocean and surface are inherently linked through tidal deformation of the floating ice shell, and tidal flexing and nonsynchronous rotation generate stresses that fracture and deform the surface to create ridges and bands. Dark spots, domes, and chaos terrain are probably related to tidally driven ice convection along with partial melting within the ice shell. Europa's geological activity and probable mantle contact permit the chemical ingredients necessary for life to be present within the satellite's ocean. Astonishing geology and high astrobiological potential make Europa a top priority for future spacecraft exploration, with a primary goal of assessing its habitability.

The mutual phenomena between Jupiter and Saturn's satellites occur every half orbital period of these planets, when the Earth and the Sun cross their equatorial plane. At Physics and Astronomy Department of Catania University the events between Jupiter's satellites have been observed during the 1973, 1979, 1985/86, 1991, 1997 and 2009 campaigns and the ones between Saturn's satellites during the 1980/81 and 1995 campaigns. An overview of the main results obtained since 1973 is presented.

Galileo's talents in perspective and chiaroscuro drawing led to his images of the Moon being accepted relatively quickly as the naturalistic portrayal of a truly physical place. In contrast to his resolved views of the Moon, Galileo saw the satellites of Jupiter as only points of light (as with stars). He thus used star symbols in Sidereus Nuncius (1610) for the moons, in constrast to an open disk for Jupiter. In this paper, I describe methods used in subsequent decades to portray objects that could not be seen in any detail but whose very existence challenged the scholastic approach to science. Within fifty years, the existence of the moons was such an accepted component of astronomy that they were depicted in the highly decorative “textbook” Atlas Coelestis seu Harmonia Macrocosmica by Andreas Cellarius (1660). Other symbolic methods, ranging from the routine to the dramatic, were used in subsequent centuries to portray the moons. Actual photographs using ground-based telescopes were not possible until the 20th century, just years before cameras on spaceflight missions captured the true details of the Medicean Stars.

Juno is the next NASA New Frontiers mission which will launch in August 2011. The mission is a solar powered spacecraft scheduled to arrive at Jupiter in 2016 and be placed into polar orbit around Jupiter. The goal of the Juno mission is to explore the origin and evolution of the planet Jupiter. Juno's science themes include (1) origin, (2) interior structure, (3) atmospheric composition and dynamics, and (4) polar magnetosphere and aurora. A total of nine instruments on-board provide specific measurements designed to investigate Juno's science themes. The primary objective of investigating the origin of Jupiter includes 1) determine Jupiter's internal mass distribution by measuring gravity with Doppler tracking, 2) determine the nature of its internal dynamo by measuring its magnetic fields with a magnetometer, and 3) determine the deep composition (in particular the global water abundance) and dynamics of the sub-cloud atmosphere around Jupiter, by measuring its thermal microwave emission.

An international effort dedicated to science exploration of Jupiter system planned by ESA and NASA in the beginning of next decade includes in-depth science investigation of Europa. In parallel to EJSM (Europa-Jupiter System Mission) Russian Space Agency and the academy of Science plan Laplace-Europa Lander mission, which will include the small telecommunication and science orbiter and the surface element: Europa Lander. In-situ methods on the lander provide the only direct possibility to assess environmental conditions, and to perform the search for signatures of life. A critical advantage of such in situ analysis is the possibility to enhance concentration and detection limits and to provide ground truth for orbital measurements. The science mission of the lander is biological, geophysical, chemical, and environmental characterizations of the Europa surface. Remote investigations from the orbit around Europa would not be sufficient to address fully the astrobiology, geodesy, and geology goals. The science objectives of the planned mission, the synergy between the Europa Lander and EJSM mission elements, and a brief description of the Laplace-Europa Lander mission are presented.

Among the most persistent popular misperceptions of Galileo is the image of an irreligious scientist who opposed the Catholic Church and was therefore convicted of heresy–was even excommunicated, according to some accounts, and denied Christian burial. In fact, Galileo considered himself a good Catholic. He accepted the Bible as the true word of God on matters pertaining to salvation, but insisted Scripture did not teach astronomy. Emboldened by his discovery of the Medicean Moons, he took a stand on Biblical exegesis that has since become the official Church position.

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.