Day 911

Wednesday.


1506.06867
A metallicity recipe for rocky planets
Dawson, Chiang, Lee

Planets with sizes between those of Earth and Neptune divide into two populations: purely rocky bodies whose atmospheres contribute negligibly to their sizes, and large gas-enveloped planets possessing voluminous and optically thick atmospheres.  Show that whether a plant forms rocky or gas-enveloped depends on the solid surface density of its parent disk.  Assembly times for rocky cores are sensitive to disk solid surface density.  Lower surface densities spawn smaller planetary embryos; to assemble a core of given mass, smaller embryos require more mergers between bodies farther apart and therefore exponentially longer formation times.  Gas accretion simulations yield a rule of thumb that a rocky core must be at least 2M_earth before it can acquire a volumetrically significant atmosphere from its parent nebula.  In disks of low solid surface density, cores of such mass appear only after the gas disk has dissipated, and so remain purely rocky.  Higher surface density disks breed massive cores more quickly, within the gas disk lifetime, and so produce gas-enveloped planets.  Test model predictions against observations, using planet radius as an observational proxy for gas-to-rock content and host star metallicity as a proxy for disk solid surface density. Theory can explain the observation that metal-rich stars host predominantly gags-enveloped planets.


1506.07135
Planck 2015 resuits. XVI.  Isotropy and statistics of the CMB
Planck Collaboration

Test the statistical isotropy and Gaussianity of the CMB anisotropies using observations made by the Planck satellite.  Results are based mainly on the full Planck mission for temperature, but also include some polarization measurements.  In particular, consider the CMB anisotropy maps derived from the multi-frequency Planck data by several component-separation methods.  For the temperature anisotropies, find excellent agreement between results based on these sky maps over both a very large fraction of the sky and a broad range of angular scales, establishing that potential foreground residuals do not affect the studies.  Tests of skewness, kurtosis, multi-normality, N-point functions, and Minkowski functionals indicate consistency with Gaussianity, while a power deficit at large angle scales is manifested in several ways, for example low map variance.  The results of a peak statistics analysis are consistent with the expectations of a Gaussian random field.  The "Cold Spot" is detected with several methods, including map kurtosis, peak statistics, and mean temperature profile.  Thoroughly probe the large-scale dipolar power asymmetry, detecting it with several independent tests, and address the subject of a posteriori correction.  Tests of directionality suggest the presence of angular clustering from large to small scales, but at a significance that is dependent on the details of the approach.  Perform the first examination of polarization data, finding the morphology of stacked peaks to be consistent with the expectations of statistically isotropic simulations.  Where they overlap, these results are consistent with the Planck 2013 analysis based on the nominal mission data and provide the most thorough view of the statistics of the CMB fluctuations to date.