Imaging of the Jupiter system with the Solid State Imaging (SSI) camera is discussed. The results of the experiment involve three main parts: imaging of phenomena in Jupiter’s atmosphere, imaging of the Galilean satellite surfaces, and imaging of the smaller satellites and ring system.

The Galileo Near Infrared Mapping Spectrometer (NIMS) is currently obtaining spectral maps of Jupiter’s moons to determine the composition and spatial distribution of minerals on the satellite surfaces. Sulfur dioxide, as a frost or ice, covers much of Io’s surface, except in hot volcanic areas. A weak spectral feature at 3.15 μm suggests the presence of an OH containing surface compound (hydroxide, hydrate, or water) and a broad absorption above 1 μm is reasonably attributed to iron-containing minerals, such as feldspars and pyrite. Water is the dominant molecule covering Europa’s surface, occurring as ice but also as a hydrate. The trailing side shows high concentrations of these hydrous minerals, whose identifications are not yet established. Ganymede’s surface exhibits water absorption bands, largely due to ice but hydrates are also present. A dark component is present, but with a smaller proportion compared to Callisto. Some of the non-ice features seen on Ganymede are similar to those found in Callisto’s spectra (see below). Among the icy Galilean satellites, Callisto shows the least amount of water ice, covering about 10% of the surface in patchy concentrations. Most of the surface is covered with unidentified (as yet) dark minerals. The exposed ice is often associated with impact craters, implying that the darker material exists as a blanket over more pure ice. Non-ice spectral features at 3.88, 4.03, 4.25, and 4.57 μm are present in Callisto’s spectra (and some of these appear in Ganymede’s spectra), each with different spatial distributions. Laboratory spectra suggest that the 4.25-μm feature is due to carbon dioxide which is trapped in the surface grains. The band at 4.03 μm may be due to sulfur dioxide, which probably originated from Io. Molecules containing CN, SH, SiH, and perhaps deuterated constituents are candidates for the other features, some of which could be derived from shock-heated and modified material from impacts, perhaps of carbonaceous composition. There is evidence for the presence of hydrated minerals on Callisto, based on water band shifts and shapes.

The Galileo orbiter and its Solid State Imaging system have increased the photographic coverage and resolution of Europa, revealing a complex surface that has been modified by tectonic deformation, impact craters on a wide range of scales, and possible cryovolcanic activity. The morphology of many of the features suggests that the depth to either liquid water or mobile-ductile ice was relatively shallow (< few kilometers) at the time of their formation. Characteristics of the mottled terrain and impact ejecta deposits suggest the presence of a shallow (˜km) subsurface zone beneath the bright icy crust. The Galileo Europa Mission, approved to continue orbital operations through 1999, will include at least nine close flybys of Europa, enabling global and regional mapping, along with high-resolution imaging of selected areas.

A conference having the title The Three Galileos: the Man, the Spacecraft, the Telescope, was held at the University of Padova from 7-10 January 1997. The conference was jointly organized by the U.S. space agency NASA, JPL, the German space agency DARA, the University and Astronomical Observatory of Padova, and the Telescopio Nazionale Galileo, with the added support of the International Astronomical Union. The scientific committee was composed of: C. Barbieri (Chairman, University of Padova), S. Atreya (University of Michigan), E. Bellone (University of Padova), M. Belton (NOAO), P. Benvenuti (ESA), F. Bertola (University of Padova), M. Calvani (Astronomical Observatory of Padova), G. Cariolaro (University of Padova), W. Ip (Max-Planck-Institute for Aeronomy), T. Johnson (JPL), T. Owen (University of Hawaii), J. Rahe (NASA), and R. West (ESO). The purpose was to discuss the discovery of the Medicean Moons by Galileo Galilei in Padova from 7-15 January 1610, the results of the Galileo spacecraft during the cruise phase and while orbiting the Jovian system, and the construction of the 3.5-m active-optics Italian telescope Galileo (TNG) in the Canary Islands.

The Infrared Space Observatory (ISO) is a cryogenically-cooled satellite giving the astronomical community, for the first time, the capability of making detailed observations at infrared wavelengths (2.5-240 ˜m) with a sophisticated and sensitive set of observatory-class instruments for a period in excess of two years.

The proposal for ISO was made to ESA in 1979 and it was selected in 1983 to be the next new start. The instruments were chosen in 1985 and ISO’s main industrial development started in 1988. Launch took place in November 1995 and the helium coolant is expected to last until April 1998. The calibration and data analysis will be improved during the post-operations phase, which is funded to the end of 2001.

Over one year and a half after its first light in orbit, the ISOCAM camera on board the Infrared Space Observatory is bringing back very exciting results. Its spectacular infrared viewing of the Universe sheds new light on the nature of the interstellar dust, on the birth of young stars embedded in dark clouds as well as on bursts of star formation in external galaxies.

The Short-Wavelength Spectrometer(SWS) is one of the four instruments on-board of ESA’s Infrared Space Observatory(ISO), launched on 15 Nov. 1995. It covers the wave-length range of 2.38-45.2μm with a spectral resolution ranging from 1000-2000. An overview is given of the in-orbit performance and a summary of the main scientific results and discoveries obtained in the first 18 months of operation of the ISO-SWS.

While all channels of the instrument (Lemke et al. 1996) are fully operational in the 21st month of the mission, some have turned out to be particularly productive: (1) far infrared mapping in the 200 /im range and (2) spectrophotometry in the middle infrared. The detection sensitivity of these modes is close to the preflight expectation. The photometric calibration of the instrument is a demanding task. Transient and memory effects of the low background detectors, responsivity drifts and spikes caused by the cosmic radiation as well as nonlinearities due to the preamps and the complex optical subsystems require corrections. Fortunately almost all of these effects are reproducable and correction algorithms are under development. While spectrophotometric (Klaas et al. 1997) and staring observations are already calibrated to better than ±20..30% in the pipeline data products, similar values will be achieved for all observing modes in the near future.

It is a pleasure for me to present, on behalf of the international consortium of scientist and engineers who built the instrument, some interim results from the Long-Wavelength Spectrometer (LWS). I shall briefly review the scientific capabilities of the instrument before describing some of the highlights of its scientific programme.

Surveys with ISO (Kessler et al 1996), in particular with the CAM (Cesarsky et al 1996) and PHOT (Lemke et al 1996) instruments, will greatly extend our understanding of extra-galactic populations and their cosmological evolution. The main advantages that ISO surveys have over e.g IRAS are increased sensitivity/depth and wavelength coverage. Within the Guaranteed and Open Time programmes there are many field surveys which will efficiently map the limits in these parameters. In this talk I will briefly overview those surveys before concentrating in more detail on one survey in particular, the ISO survey of the Hubble Deep Field (HDF), to illustrate the kind of results that can be expected.

When and how did galaxies form? In order to understand this important problem in astrophysics, many observational studies have been conducted so far. Deep survey observations in the optical are powerful for detecting very faint sources in the high-z universe The observed surface density of such high-z star forming galaxies may, however, be smaller than the value expected from the local density of luminous galaxies (e.g., Lanzetta et al. 1996; Steidel et al. 1996) and it is possible that we are missing classes of objects with substantial reddening and have not yet sampled fully the high-z counterparts of typical nearby galaxies. Since the nearby, well evolved galaxies consist of old low-mass stars, it is important to find galaxies with numerous low-mass stars. These stars emit their energy from the optical to near infrared (NIR) mostly, implying that they are more luminous in the NIR and MIR (mid-infrared) than in the optical if they were present at high redshifts.

The evolution of galaxy clusters from their formation due to the merging of sub structures, the bulk of star formation and subsequent chemical enrichment of the intra-cluster medium, is expected to be quite recent (z<l-2) in the hierarchical clustering scenario (White & Frenk 1991).

All the ISO instruments are contributing to the study of activity in galaxies of essentially all types. Although AGN's as such are pointlike, the beautiful CAM image of CenA shown by Catherine Cesarsky has given us the clearest view so far of its visually obscured nucleus and surrounding spiral disc embedded in an elliptical galaxy. The CAM CVF is also providing spectral images of the PAH features and important diagnostic ionic lines (e.g [NeII] and [NeIII]) in the circumnuclar regions of AGN and merging starburst systems (Vigroux et al., 1996). PHT is providing detailed spectral energy distributions over the complete 2.5-240µm range and PHTS is proving invaluable for assembling a catalogue of low resolution (R ⋍ 90) galaxy spectra covering the 6-12µm PAH features. SWS and LWS are generating higher resolution (R ⋍ 2000-200) spectra over the range 2.5-200µm such as that shown in Fig. 1. of the Circinus galaxy which exhibits both AGN and starburst activity and well illustrates the wide range of diagnostic features, many seen for the first time, accessible to ISO studies of galaxies. It shows the overall continuum with a peak around 100µm; PAH features and Si absorption which dominate the spectrum around 10µm; H recombination lines; H2 pure rotational emission lines; low ionization potential ionic lines excited by starburst activity and high excitation lines (up to ⋍ 300eV) excited by the visually obscured AGN.

Based on results from the first half of its mission, ISO (Kessler et al. 1996) is contributing to our understanding of normal galaxies by offering effective gauges of the physical conditions within the interstellar medium (ISM) of galaxies. ISO data permit a more precise and detailed characterization of the radiation, dust and gas deep within many more galaxies than had been previously possible. This in turn yields new insight into the regulation mechanisms of star formation and galaxy evolution. Apart from these ISM diagnostics, ISO also contributes a vastly improved empirical description of galaxies at all infrared wavelengths, which will be critical in guiding the search for the origins and early life of galaxies.

With all its instruments, ISO is sensitive to temperatures in the range ~ 30 – 2000 K. This range is particularly adapted to studies of dense interstellar matter (gas and dust) in cold clouds, and to material associated with very early stages of stellar evolution: circumstellar matter around low-mass stars (disks, envelopes), outflows generated by them and interactions with the surrounding medium.

Circumstellar matter is found almost exclusively around young stars that have not yet reached the main sequence and around old stars that have left this sequence. Some main sequence stars still carry the remnants of a disk of dustlike material as a remnant of their time of formation.

Among the important contributions of ISO to the physics of the interstellar medium, this paper concentrates only on the emission from the solid phase (the interstellar grains) and the small atom clusters which are the bridge between the grains and the small molecules with less than about 10 atoms.

Among the important contributions of ISO to the physics of the interstellar medium, this paper concentrates only on the emission from the solid phase (the interstellar grains) and the small atom clusters which are the bridge between the grains and the small molecules with less than about 10 atoms.