Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Organic Molecules and the Coloration of Jupiter

Abstract: Jovian atmosphere simulation with energy from corona discharge, producing simple organic molecules

Rocky planet formation: quick and neat

Abstract: We reconsider the commonly held assumption that warm debris disks are tracers of terrestrial planet formation. The high occurrence rate inferred for Earth-mass planets around mature solar-type stars based on exoplanet surveys (roughly 20%) stands in stark contrast to the low incidence rate (less than 2-3%) of warm dusty debris around solar-type stars during the expected epoch of terrestrial planet assembly (roughly 10 Myr). If Earth-mass planets at AU distances are a common outcome of the planet formation process, this discrepancy suggests that rocky planet formation occurs more quickly and/or is much neater than traditionally believed, leaving behind little in the way of a dust signature. Alternatively, the incidence rate of terrestrial planets has been overestimated or some previously unrecognized physical mechanism removes warm dust efficiently from the terrestrial planet region. A promising removal mechanism is gas drag in a residual gaseous disk with a surface density of roughly or somewhat more than 0.001% of the minimum mass solar nebula.

Semiannual variation in the heterosphere: A reappraisal

Abstract: Past attempts to represent the semiannual density variation in the heterosphere as a consequence of temperature variation have run into difficulties in two height regions: below 200 and above 1000 km. The main argument in favor of the temperature variations was the dependence of their amplitude on the solar cycle; it can be shown, however, that this dependence is spurious, being caused by the variation of the density change dρ/dT with the temperature T. An analysis of the semiannual density variations at different height levels fails to show a dependence of the amplitude with the sunspot cycle. All difficulties are removed if we assume that the semiannual density variation is not a direct consequence of temperature variations.

Localized Magnetic-field Structures and Their Boundaries in the Near-Sun Solar Wind from Parker Solar Probe Measurements

Abstract: Author(s): Krasnoselskikh, V; Larosa, A; Agapitov, O; De Wit, TD; Moncuquet, M; Mozer, FS; Stevens, M; Bale, SD; Bonnell, J; Froment, C; Goetz, K; Goodrich, K; Harvey, P; Kasper, J; Macdowall, R; Malaspina, D; Pulupa, M; Raouafi, N; Revillet, C; Velli, M; Wygant, J | Abstract: One of the discoveries of the Parker Solar Probe during its first encounters with the Sun is ubiquitous presence of relatively small-scale structures standing out as sudden deflections of the magnetic field. They were named "switchbacks" since some of them show a full reversal of the radial component of the magnetic field and then return to "regular" conditions. We carried out an analysis of three typical switchback structures having different characteristics: I. Alfvenic structure, where the variations of the magnetic field components take place while conserving the magnitude of the magnetic field; II. Compressional structure, where the magnitude of the field varies together with changes of its components; and III. Structure manifesting full reversal of the magnetic field, presumably Alfven, which is an extremal example of a switchback. We analyzed the properties of the magnetic fields of these structures and of their boundaries. Observations and analyses lead to the conclusion that they represent localized twisted magnetic tubes moving with respect to surrounding plasma. An important feature is the existence of a relatively narrow boundary layer at the surface of the tube that accommodates flowing currents. These currents are closed on the surface of the structure and typically have comparable azimuthal and tube-axis-aligned components. They are supported by the presence of an effective electric field due to strong gradients of the density and ion plasma pressure. The ion beta is typically larger inside the structure than outside. The surface of the structure may also accommodate electromagnetic waves that assist particles in carrying currents.