A proposed search of the solar neighborhood for substellar objects

The Infrared Astronomical Satellite (IRAS) program will produce an extremely sensitive all-sky survey over the wavelength region 8 to 120 μm when the mission is flown in 1982. These data will provide a novel opportunity to detect planetary-sized objects having masses <0.08M_⊙ or near our solar system. The improved detection limit of the IRAS will greatly increase the volume of space searched for such objects as compared with previous optical and infrared studies.     

Protoplanetary core formation by rain-out of minerals

Models of giant gaseous protoplanets calculated by DeCampli and Cameron (1979) indicate that iron and probably other minerals in the interior of a planet would be in the liquid state during part of the protoplanet evolution. Liquid drops in a protoplanet would grow by coalescence much as cloud drops in the Earth's atmosphere grow to rain drops. We have modeled this process by using the stochastic collection equation (Slattery, 1978) for various initial conditions. In all of the cases considered, the growth time (to centimeter-sized droplets) is much shorter than the time, as estimated by detailed evolutionary calculations, that the drops are in the liquid state. Brownian collection is effective in quickly coalescing tiny liquid droplets to an average radius of about 0.005 cm with very few drops remaining with radii less than 0.001 cm. For radii larger than 0.005 cm gravitational collection is dominant. Since the particles are rapidly swept from interstellar grain sizes to much larger sizes, the opacity in the cloud layer is expected to drop sharply following melting of the grains.     

O VI (λ = 1032 Å) profiles in and above an active region prominence,compared to quiet Sun center and limb profiles

O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s^–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s^–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 10⁶ K, and a non-thermal velocity (NTV) of 49 km s^–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines.     

Study of Mars dynamics from lander tracking data analysis

After the touchdown of the two Viking landers on Mars, radio tracking measurements have been performed between them and Earth-based stations. With use of the first 9 months of data, we have improved the rotation rate and the mean orientation of the spin axis of Mars, referred to its mean orbit. For the first time, some nutations terms have also been estimated. Nevertheless the precise determination of the spin axis motion will require additional data collected during the extended mission. Our solution includes also the lander locations and the relativistic parameter .Paper presented at the European Workshop on Planetary Sciences, Organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.     

The surface of Io: Geologic units,morphology, and tectonics

A prelimanary geologic map, representing 26.5% of the surface of Io, has been compiled using best-resolution (0.5 to 5 km/line pair) Voyager 1 images and (as a base) a preliminary pictorial map of Io. Nine volcanic units are identified, including materials of mountains (1.9% of total area), plains (49.6%), flows (31.1%), cones (0.1%), and crater vents (4.0%), in addition to seven types of structural features. Photogeologic evidence indicates a dominantly silicate composition for the mountain material, which supports heights of at least 9 ± 1 km. Sulfur flows of diverse viscosity and sulfur-silicate mixtures are thought to compose the pervasive plains. Pit crater and shield crater vent wall scarps reach heights of 2 km and layered plains boundary scarps have estimated heights of 150 to 1700 m; such scarps indicate a material with considerable strenght. A cumulative, volcanic crater size-frequency distribution plot has been prepared using 170 mapped Ionian vents with diameters > 14 km; the shape and slope of the curve are like those for impact craters on other bodies in the solar system, attesting to a similar nonrandom distribution to crater diameters and a surplus of small craters. Io's equatorial zone has six times the number of vents per unit area as the south polar zone. No craters of unequivocal impact origin have been identified on Io to date. A total of 151 lineaments and grabens are recognized with four dominant azimuthal trends forming two nearly orthogonal sets spaces 110° apart (N 85° E, N 25° W and N 45° E, N 55°W). The mapped area lies within the longitudinal zone (250 to 323°) of least-abundant SO₂ frost, indicating that other sulfurous components dominate the upper surface layers in this area.     

The temperature of interstellar iron grains

In order for catalytic reactions to occur in interstellar dust clouds, it is necessary for the temperature of the grains to be about an order of magnitude hotter than usually calculated for grains of dielectric materials. However, transition metal (e.g., iron) grains should be fairly abundant, and because they absorb strongly in the visible and ultraviolet regions of the interstellar radiation field, they have equilibrium temperatures 133 K. This was determined by a new method which utilizes Semi-Empirical free electron theory parameters in the infrared, coupled with a reiteration scheme which takes into consideration the change of conductivity of the iron with temperature.     

Secular brightness increases of Titan,Uranus, and Neptune, 1972–1976

The brightnesses of Titan, Uranus, and Neptune in b (4718 ÅA) and y (5508 ÅA) have increased linearly since 1972 at rates ranging from 0.005 to 0.025 mag yr^?1. The observations were made differentially on a number of nights each season with respect to a network of comparison stars whose relative magnitudes were determined by independent measurements. Solar phase coefficients were derived for each object, and all observations have been normalized to zero solar phase angle and mean heliocentric distances. No explanation for the changes has been found, but a possible influence of solar activity upon planetary albedo is suggested by the fact that all of the objects observed have brightened during the declining half of the solar cycle.     

Green's theorem and Green's functions for the steady-state cosmic-ray equation of transport

Green's Theorem is developed for the spherically-symmetric steady-state cosmic-ray equation of transport in interplanetary space. By means of it the momentum distribution functionF _o(r,p), (r=heliocentric distance,p=momentum) can be determined in a regionr _arr_bwhen a source is specified throughout the region and the momentum spectrum is specified on the boundaries atr _a andr _b . Evaluation requires a knowledge of the Green's function which corresponds to the solution for monoenergetic particles released at heliocentric radiusr _o , Examples of Green's functions are given for the caser _a =0,r _b = and derived for the cases of finiter _a andr _b . The diffusion coefficient is assumed of the form = _o(p)r ^b . The treatment systematizes the development of all analytic solutions for steady-state solar and galactic cosmic-ray propagation and previous solutions form a subset of the present solutions.     

Comparison between some Hα and X-ray flares

In the present paper, H-evolutive curves of chromospheric events are compared with flux evolutive curves of X-ray events observed at the same time in different spectral regions. A correspondence between the emissions E(I _H/I _chr)'s at higher and higher H-intensity levels, and the X-ray fluxes F()'s in harder and harder -ranges is shown. Further, the present observations seem to indicate the existence of a single triggering mechanism during the flash-phase of a flare. It is also shown that these results may be in agreement with Brown's model for chromospheric flares.