"The Three Galileos" Conference in Padova

Gabriele Cremonese (1), Francesca Rampazzi (2)

(1) Osservatorio Astronomico di Padova, (2) Consorzio Padova Ricerche

In the days from January 7 to 10, some of the very dates in which Galileo discovered Jupiter's Medicean moons, Padova hosted the international conference "The Three Galileos: the Man, the Spacecraft, the Telescope" jointly promoted by The University and Astronomical Observatory of Padova, by NASA-JPL and by the German space agency DARA.

A solemn ceremony preceded the opening of the conference proper: while the notes of Gaudeamus igitur... arose in the suggestive atmosphere of the Aula Magna Galileo Galilei, honorary doctorates were presented to Franco Preparata (Brown University, USA, in Engineering) William J. O'Neil and Torrence V. Johnson (Jet Propulsion Laboratory, USA, both in Astronomy) by the University Rector Prof. Giovanni Marchesini. (Image of honorees)

The students surprised the honorees with joke gifts and laurel wreaths following our old tradition.

The conference was then opened by its chairman, Cesare Barbieri (Padova University, TNG), who presented the Rector of the University with two precious gifts: the first is a copy of a letter by Galileo, reproduced by kind permission of the Special Book Collection of the Univesity of Ann Arbor (Michigan), the second is a watercolour titled The Three Galileos by the contemporary american artist Greg Mort, and painted following a visit to our University.

The historical part on the man Galileo began with a talk by G.Coyne, Director of the Vatican Observatory and also a past honorary doctor in Astronomy from our University. Coyne pointed out how Galileo's notes were the first really new empirical data in over 2000 years, beginning the fascinating adventure of the interplay of theory and observations.

A subtle philosophical discussion was presented by E.Bellone, and finally C.Bellinati showed images of the houses of Galileo in Padova.

Several most awaited talks were devoted to the first results coming from the observations of the Galileo spacecraft and of the Probe. Other review talks expounded the present knowledge on the jovian system.

The Galileo mission indeed has already surpassed expectations by allowing to better understand the formation of Jupiter, of its atmosphere and of its interior; and there is still more to come, to the general benefit of our knowledge about the whole Solar System.

The data coming from the Galileo spacecraft, altough not completely reduced, provide already some very interesting views of the planet and of the satellites, starting with the measurements of the atmosphere of Jupiter given by the Probe.

The Probe made there a fiery descent on December 7, 1995. Many instruments, particularly the mass spectrometer and the nephelometer, measured the composition and the cloud structure of Jupiter to a pressure of 20 earth atmospheres which was reached at a depth of approximately 150 kilometers below the visible clouds. As a result of these measurements and complementary data from the Galileo Orbiter, significant new insight has been gained about the gas composition, clouds, meteorology, and the formation of the planet.

It has been found that relative to hydrogen, namely the main atmospheric gas, the abundances of sulfur and carbon (present mainly in form of methane and hydrogen sulfide) are two to three times greater than on the Sun. This was surprising since the compositon of Jupiter and the Sun was expected to be the same, as no evolution over time should have occurred on Jupiter because its great mass would prevent the escape of even the lightest of gases from its atmosphere. The above finding gives a clue to the importance of icy planetesimals (comets) in the observed characteristics of Jupiter. The ice can trap gases such as methane and hydrogen sulfide but not hydrogen, helium or neon.

The atmosphere was also found to contain a very small abundance of heavy organic molecules. Contrary to predictions, the Probe entry site was relatively clear, with only two very wispy clouds. Relatively massive cumulus-type clouds of water, ammonium hydrosulfide and ammonia were expected. Instead, there was no indication of a water cloud and the other two clouds were very thin and cirrus-like.

Sushil Atreya and Tobias Owen suggested that local meteorology in the form of a large downdraft in the Probe region is responsible for this behaviour, and that outside such regions Jupiter should exhibit the predicted cloud structure discussed above.

In the last few months the spacecraft started to provide the first sequence of images of the four Galilean satellites and very soon important and unexpected results appeared.

One of the most interesting findings comes from Europa, the second Galilean satellite, that shows a stunning surface structure not easily explainable by simply considering it as an icy body. Till two years ago Europa was believed an icy body covered by water ice and without an atmosphere, but HST, in 1993, showed that it has a very tenuous O2 atmosphere. Soon after M.Brown, and also observations taken at our Observatory in Asiago, revealed low abundances of sodium.

At the moment such data need a more detailed explanation and modelling, but Europa appears to be quite complex, with strong interactions with the magnetosphere of Jupiter and the plasma torus surrounding the planet at the Io's orbit. Very high resolution images from the Galileo spacecraft showed some regions of the surface very poor of large impact craters and with some strong evidence of a fast and important resurfacing.

All these new discoveries brought R.Greeley to say that there is a high probability to find a very large ocean of liquid water beneath the first surface layers of the satellite. In such a way it is possible to explain the fresh structures on the surface without considering a real vulcanic activity, very difficult to understand for Europa and its interior.

One of the most important topics of the spacecraft's observations is Io, the first galilean satellite, because of the strong interations with the gravitational field of Jupiter, the jovian magnetosphere and the orbital resonance with the satellites Europa and Ganimede.

Io is one of most active body of the Solar System and soon the first images of the satellite taken by the Galileo showed an impressive plume coming from a strong vulcanic eruption on its surface. The images of the calderas showed interesting features in their structure and in the material distributed on the surface. Furthermore some scientists started to compare such images with those obtained from the Voyager missions more than 17 years ago.

A most relevant discovery on Io has been a faint magnetic field that could change dramatically our view of the satellite interior and the interactions with the plasma torus and jovian magnetosphere. The search for a source of such magnetic field is quite delicate, but not so difficult, as inside the satellite strong frictions occur due to the gravitational interaction with Jupiter and the Laplace resonance with Europa and Ganimede, that constrain its orbital eccentricity providing an huge level of internal energy. Such energy could allow the creation of a large mass of liquid metal in the innermost regions of the satellite working as a dinamo.

If it is not easy to find an explanation to the magnetic field of Io it is even more difficult to understand such a discovery on Ganimede. The magnetic measurements performed by the spacecraft during the first fly-by with Ganimede, the third galilean satellite, showed the presence of a very faint magnetic field. In this case there is no strong gravitational interaction, and the scientists are not able to understand what could be the source and how different the satellite interior could be from the predicted models.

Such discovery is not completely confirmed; the debate is open considering also the strange behaviour of the magnetic field lines around Ganimede. An alternative explanation could come from an unforseeable interaction with the jovian magnetosphere.

All these exciting results have been debated in lively interesting discussions at the Conference; but surely discussion will continue in the next months and maybe years when other data will be added and the first precise modelling will be applied. NASA is considering an extension of the Galileo mission to perform further measurements on Europa, that becomes now an important object for the exobiology community.

In the third part of the conference the technical characteristics of the TNG were described in detail.

F.Bortoletto (Astronomical Observatory of Padova) discussed its active optics system showing for the first time precise measurements on the movement control of the exapod of the secondary mirror, while R.Ragazzoni (Astronomical Observatory of Padova) had the first experimental data on a pyramid sensor to be used as wavefront sensor for adaptive optics.

S.di Serego (Astrophysical Observatory of Arcetri) described the general operation management and the advantages of service observing, remote observing and queue scheduling.

A round table panel on the Exploration of the Solar System, chaired by Prof. L. Woltjer, President of the IAU, has witnessed, among other arguments, the stimulating debate between J.Rahe (NASA) and R.Giacconi (ESO). The first stressing the importance of careful planning, the second pointing out how missions often precede planning.

D. Hunten speaking for himself, added a spicy touch of scientific interest surviving through the many selection steps of the mammouth-sized international organisations. Planning was also greatly stressed, at the European and national levels, by R.Bonnet (ESA) and S.Di Pippo (ASI).

M.Marov (Keldysh Institute of Applied Mathematics, Russian Academy of Science) expressed his deep concern for the future of space research in his Country after the loss of Mars 96 and the cancelling of Mars 98 (see his interview in this issue).

C.Barbieri expressed his concern for the future of many students, who are attracted by the beauties of the astronomical studies, but then find it almost impossibile to stay in the research field for lack of positions. This argument was further expanded by G.Setti on behalf of the National Council of the Astronomical Research (CRA), in the context of the peculiar present Italian situation, while J.Geiss presented the activities promoted in this field by the International Space Science Institute (ISSI) of Bern.

Among the social events a special mention must be given to the organ concert with music from Galileo's time offered in S.Antony's Cathedral by L.J.Deutsch (JPL, CalTech) who designed the inflight recovery of the Galileo mission using the spacecraf's low-gain antenna.

The conference closed with two momentous events: the presentation to the attendees of some rare fist original editions of works by Galileo, Copernico, T.Brahe, from the private collection of G.Beltrame, and the preview of the exhibition Voyage in the Cosmos, to be opened to the public later in January, but whose first section "From the man Galileo to the Galileo spacecraft" was already completed.

The relevance of the scientific talks and the large international attendance to this conference in its setting of great historical significance, are all positive signs for future collaboration.

On Saturday January 11, Pope John Paul II granted the conference attendees a private audience in the Vatican and expressed great interest for their scientific work urging them always to be conscious of the moral and human aspect of research.

The delegation was then given a very kind hospitality at the Vatican Observatory in Castelgandolfo with a buffet and a visit to the specola and the beautiful gardens of the papal villa under the precise guide of G.Coyne.

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