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Recent space observations of cometary nuclei show evidence of internal (cryovolcanic) activity while retaining aspects of their primitive origins. Using discoveries made during the two most recent cometary encounters: EPOXI at 103P/Hartley 2 and Stardust-NExT at 9P/Tempel 1, we test a hypothesis for their physical evolution, which, if true, could provide a unified basis for understanding the relative ages of their surfaces and the causes of a wide range of cometary activity. We show: (i) that the categorization of 103P/Hartley 2 as hyperactive is not a reflection of the extent of activity over the surface of the nucleus for which we find a normal [H.sub.2]O production rate; (ii) that the heterogeneous spatial distribution of C[O.sub.2] and [H.sub.2]O in the inner comae of 9P/Tempel 1 and 103P/Hartley 2 is best explained by processes associated with cometary activity rather than the presence of primitive compositional heterogeneities in the nucleus; and (iii) that most of the quasi-circular depressions seen on the surface of 9P/Tempel are the result of outburst activity. The apparent absence of circular depressions and large scale layering on 103P/Hartley 2 present a challenge to the evolutionary hypothesis although the small size of its nucleus may ultimately provide an explanation. PACS Nos.: 96.25.Bd, 96.30.Cw Resume: Les observations recentes de coeurs de cometes mettent en Evidence une activity interne de cryovolcanisme, tout en retenant les aspects de leur origine. Tablant sur les decouvertes faites lors des deux dernieres rencontres de cometes: EPOXI avec 103P/Hartley 2 et Stardust-NExT avec 9P/Tempel 1, nous verifions une hypothese sur revolution physique de ces cometes qui, si elle se verifie, pourrait fournir une base uniforme pour comprendre Page relatif de leurs surfaces et les causes d'un large domaine d'activites cometaires. Nous insistons sur les points suivants : (i) que la classification de 103P/Hartley 2 comme hyperactive n'est pas une reflexion de l'etendue de l'activite a la surface du noyau, caracterisee par une production normale de [H.sub.2]O; (ii) que la distribution spatiale heterogene de C[O.sub.2] et de [H.sub.2]O, observee dans le coma interne de 9P/Tempel 1 et de 103P/Hartley 2, est mieux expliquee par des mecanismes associes & l'activite cometaire plutot qu'a la presence d'une composition heterogene primitive dans le noyau; et (iii) que la plus grande partie des depressions quasi-circulaires vues a la surface de 9P/Tempel 1 resulte d'expulsions violentes. L'absence apparente de depressions circulaires et la stratification a large echelle sur 103P/Hartley 2 presentent un defi a l'hypothese evolutive, merie si la petitesse de son noyau pourra eventuellement fournir une explication., Don Hunten and comets To my knowledge, Don Hunten authored only a few papers concerning comets [1-3] and they were really more about the atmosphere of Jupiter than about the [...]

Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not hte mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expenses of ancient mare basalts. The inside of the far side South Pole--Aitken basinc (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta., THE GALILEO SPACECRAFT ENCOUNTERED THE EARTH-moon system in December 1990 in the first of two flybys that are part of a sequence of planetary gravity assists that will deliver the [...]

THE SOLID STATE IMAGING (SSI) camera on Galileo returned 77 useful images from Venus documenting the dynamical state of the cloud tops during the week after the encounter on 10 [...]

High resolution images obtained by the Galileo spacecraft present new information about wedge-band formation on Europa. It can be seen that a zone of dark, wedge-shaped bands extends WSW to around 40 degrees S, 250 degrees W in a prominent belt, 2,000 km by 600 km. The centre of the zone is around 15 degrees S, 215 degrees W, southwest of the anti-Jupiter point. It seems likely that plate fracturing and movement in response to regional surface stresses permitted material to rise passively to the surface to create the dark bands.

High-resolution Galileo spacecraft images of Jupiter's moon Europa indicate the existence of mobile 'icebergs.' There is convincing evidence for the existence of liquid water at shallow depths below the surface, either now or at some point in the past. It appears that the mobile layer, either water or warm ice, is or was widespread, and not limited to the small area studied. The processes that have disrupted Europa's plains are almost certainly continuing at present.

Two Soviet, two Japanese, one European, and one American spacecraft are in interplanetary space on their way to a scientific encounter with Halley's comet. Before this 'swarm' (1) of spacecraft [...]