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Abstract—We present results of visible wavelengths spectroscopic measurements (0.45 to 0.72 microns) of two binary asteroids, obtained with the 1‐m telescope at the Wise Observatory on January 2008. The asteroids 90 Antiope and 1509 Esclangona were observed to search for spectroscopic variations correlated with their rotation while presenting different regions of their surface to the viewer. Simultaneous photometric observations were performed with the Wise Observatory's 0.46 m telescope, to investigate the rotational phase behavior and possible eclipse events.

The total amount of melt produced in Mars during its evolution is estimated by means of a parameterized, one-dimensional, analytic mantle convection model that assumes a stagnant lid and whole mantle convection. The fertility of the mantle—defined as the potential to create basalt—and its variation with time are taken into account. The model is composed of core, mantle, and lithosphere, with two boundary layers separating them. The contributions to volcanism by pressure release melting (PRM), and by plumes from the core–mantle boundary layer, are compared and discussed. We show that such models tend to produce considerable melting during the early evolution of the planet, and that the amount of melting depends strongly on the abundances of radioactive elements. Although the model's assumptions may not be valid for the early evolution of the planet, the model is relevant to the later history, which is insensitive to initial conditions. We find that PRM volcanism should have ceased between 1 and 2.5 Byr ago and any recent volcanic activity must have originated in plumes.

The initial structure of a comet nucleus is most probably a homogeneous, porous, fine-grained mixture of dust and ices, predominantly water. The water ice is presumably amorphous and includes considerable fractions of occluded gases. This structure undergoes significant changes during the early evolution of the nucleus at large heliocentric distances, due to internal radiogenic heating. Structural changes occur mainly as a result of gas flow through the porous medium: the gas pressure that builds up in the interior is capable of breaking the fragile structure and altering the pore sizes and porosity. These effects are modeled and followed numerically, testing a large number of parameters.

We describe a Monte Carlo model that simulates dust migration in a porous cometary nucleus. We present computations for media in which the pore-size distributions are either random or normal; additional computations indicate that media with power-law size distributions behave very similarly to random distributions. We show how the average time to cross the medium varies as a function of porosity and how the structure of the medium varies with time. Implications for the structure of the cometary nucleus are discussed.

Radioactive heating is the main energy source of comets residing in the distant parts of the Solar System. It should determine whether liquid water could have existed in comets and whether comets, presumably formed of amorphous ice, could have retained the ice, at least partly, in this pristine form. Thermal evolution calculations of relatively large (over 10 km in radius), porous comet nuclei are performed for many different initial parameter combinations. The radioisotopes considered are ⁴⁰K, ²³²Th, ²³⁵U, and ²³⁸U, in meteoritic abundances, as well as ²⁶Al, in various initial abundances. We allow for heat conduction through the ice-dust matrix, as well as advection by flowing gases. Crystallization of the amorphous ice accompanied by release of occluded gases, and sublimation/condensation from/ onto the pore walls are taken into account. We find that porous comet nuclei may emerge from the long-term evolution in three different configurations, depending on the thermal conductivity, porous structure, radius, etc.: (a) preserving their pristine structure throughout; (b) almost completely crystallized (except for a relatively thin outer layer), and (c) having a crystallized core, a layer of frozen gas (originally occluded in the amorphous ice) and an outer layer of unaltered pristine material. Liquid cores may be obtained only if the porosity is negligible. The extent of such cores and the length of time during which they remain liquid are again determined by initial conditions, as well as by physical properties of the ice. If, in addition to the very low porosity, the conductivity were extremely low, it should be possible to have both an extended liquid core, for a considerable period of time, and an outer layer of significant thickness that has retained its original pristine structure. Copyright 1995, 1999 Academic Press

The evolution of a 1.25M⊙ carbon and oxygen (equal fractions by mass) homogeneous star is followed by means of a computer code capable of dealing with dynamic evolutionary phases.

An evolutionary scenario for classical novae is proposed, which is intended to solve the discrepancies that exist between theory and observations:the space densities of classical novae deduced from surveys in the solar neighbourhood are lower by about two orders of magnitude than those predicted theoretically, and the mass transfer rates in nova binaries, as estimated from observed luminosities in quiescence, are higher than those allowed by the thermonuclear runaway model for nova outbursts. These discrepancies disappear if mass transfer (at a high rate) takes place for only a few hundred years before and a few hundred years after an eruption, but declines afterwards and remains off for most of the time between outbursts. We show that such a behavior is to be expected if one takes into account the variation of binary separation, due to mass ejection on the one hand and angular momentum losses on the other hand.

A theoretical model of aerodynamic heating of a meteoric particle upon entry into a parent body atmosphere is presented. The model includes the effects of melting, vaporization, and heat conduction into the particle interior. Properties of chondrule rims are interpreted in the context of the model. We conclude that the formation of true melt rims by atmospheric entry requires that a low-melting-temperature component be fractionated in the outer part of the chondrule prior to rim formation, and that the range of thermal alteration effects observed in UOC chondrites reflects the variety of encounter conditions and chondrite types. Further tests of the model are suggested.

A classical nova model was evolved through a complete cycle, i.e. accretion leading to cutburst, mass loss and again accretion, ending in another outburst, by means of an implicit Lagrangian hydrodynamic code, which included diffusion (concentration, pressure and thermal terms), as well as an extensive nuclear reactions network between 28 isotopes of C, N, O, F, Ne, Na, Mg and Al. The initial model was a 1.25 M? C-O white dwarf (WD) and the accretion rate assumed was 10-11 M?/yr. For more details of this calculation, see Prialnik (1986).

Numerical simulations of the evolving activity of comet Hale-Bopp are presented, assuming a porous, spherical nucleus, 20 km in radius, made of dust and gas-laden amorphous ice. The main effects included are: crystallization of amorphous ice and release of occluded gas, condensation, sublimation and flow of gases through the pores, changing pore sizes, and flow of dust grains. The model parameters, such as initial pore size and porosity, emissivity, dust grain size, are varied in order to match the observed activity. In all cases, a sharp rise in the activity of the nucleus occurs at a large heliocentric distance pre-perihelion, marked by a few orders of magnitude increase in the CO and the CO2fluxes and in the rate of dust emission. This is due to the onset of crystallization, advancing down to a few meters below the surface, accompanied by release of the trapped gases. A period of sustained, but variable, activity ensues. The emission of water molecules is found to surpass that of CO at a heliocentric distance of 3 AU. Thereafter the activity is largely determined by the behaviour of the dust. If a dust mantle is allowed to build up, the water production rate does not increase dramatically towards perihelion; if most of the dust is ejected, the surface activity increases rapidly, producing a very bright comet.