Day 588

Thursday.

1402.2650
The scientific case for a mission to the ice giant planets with twin spacecraft to unveil the history of our Solar System
Turrini et al

Exploration of ice giant planets Uranus and Neptune---"a timely milestone, fully appropriate for an L class mission" (Cosmic Vision 2015-2025).  Explore both planets and satellites in the framework of a single L-class mission.  Goals: comparatively studying these two similar yet extremely different systems, sheds new light on the ancient past of the SS and on the processes that shaped its formation and evolution.  This would reveal whether the SS and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation.  Also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy.  Also allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and the behavior of the solar wind and the interplanetary B-field.

1402.2655
An HST/COS survey of the low-redshift IGM. I. Survey, methodology, & overall results
Danforth et al

Spectra of 75 bright AGNs at z<0.85, get 4369 individual absorption lines.  The column-density distribution of HI systems is seen to evolve both in amplitude and slope at z<0.47.  Observe 985 metal lines in 354 systems, and find that the fraction of absorbers detected in metals is strongly dependent on HI column density.  OVI absorbers appear to evolve in the same sense as the Lya forest.  A velocity-space 2-pt correlation function shows substantial clustering of HI absorbers on scales of Delta nu=50-300 km/s with no significant clustering at larger Delta nu.  Most of the clustering signal comes from the stronger (N_HI>1e13.5 cm^-2) absorbers particularly those with metal absorption.  The full catalog of absorption lines and fully-reduced spectra is available via MAST as a high-level science product at archive.stsci.edu/prepds/igm/.

1402.2670
Robust weak-lensing mass calibration of Planck galaxy clusters
von der Linden, Mantz, Allen, Applegate, et al

Tension between Planck SZ cluster sounds and CMB temperature anisotropies: compare Planck cluster mass estimates with robust, WL mass measurements from Weighting the Giants (WtG) project.  For the 22 clusters in common, find overall mass ratio of <M_Planck/M_WtG>=0.688pm0.072.  Extending those not used in Planck cosmology analysis yields similar values, for the 38 clusters in common.  Identifying the WL masses as process for the true cluster mass (on average), these ratios are ~1.6 sigma lower than the default mass bias of 0.8 assumed in the Planck cluster analysis.  Adopting the WtG WL-based mass calibration would substantially reduce the tension found between the Planck cluster count cosmology results and those from CMB temperature anisotropies. Also find modest evidence (95% CL) for a mass dependence of the calibration ratio and discuss its potential origin in light of systematic uncertainties in the temperature calibration of the X-ray measurements used to calibrate the Planck cluster masses.  Results exemplify the critical role that robust absolute mass calibration plays in cluster cosmology, and the invaluable role of accurate WL mass measurements.