Velocity anti-correlation of diametrically opposed galaxy satellites in the low-redshift Universe
Nature 511, 7511 (2014). doi:10.1038/nature13481
Authors: Neil G. Ibata, Rodrigo A. Ibata, Benoit Famaey & Geraint F. Lewis
Recent work has shown that the Milky Way and the Andromeda galaxies both possess the unexpected property that their dwarf satellite galaxies are aligned in thin and kinematically coherent planar structures. It is interesting to evaluate the incidence of such planar structures in the larger galactic population, because the Local Group may not be a representative environment. Here we report measurements of the velocities of pairs of diametrically opposed satellite galaxies. In the local Universe (redshift z < 0.05), we find that satellite pairs out to a distance of 150 kiloparsecs from the galactic centre are preferentially anti-correlated in their velocities (99.994 per cent confidence level), and that the distribution of galaxies in the larger-scale environment (out to distances of about 2 megaparsecs) is strongly clumped along the axis joining the inner satellite pair (>7σ confidence). This may indicate that planes of co-rotating satellites, similar to those seen around the Andromeda galaxy, are ubiquitous, and their coherent motion suggests that they represent a substantial repository of angular momentum on scales of about 100 kiloparsecs.
Planetary science: Titan's sea is super salty
Nature 511, 7509 (2014). doi:10.1038/511266b
Saturn's largest moon, Titan, has a buried ocean that is saltier than many seas on Earth.Titan, with its thick atmosphere and bodies of surface liquid, is of great interest to scientists looking for life beyond Earth. A team led by Giuseppe Mitri, of the
A deep crust–mantle boundary in the asteroid 4 Vesta
Nature 511, 7509 (2014). doi:10.1038/nature13499
Authors: Harold Clenet, Martin Jutzi, Jean-Alix Barrat, Erik I. Asphaug, Willy Benz & Philippe Gillet
The asteroid 4 Vesta was recently found to have two large impact craters near its south pole, exposing subsurface material. Modelling suggested that surface material in the northern hemisphere of Vesta came from a depth of about 20 kilometres, whereas the exposed southern material comes from a depth of 60 to 100 kilometres. Large amounts of olivine from the mantle were not seen, suggesting that the outer 100 kilometres or so is mainly igneous crust. Here we analyse the data on Vesta and conclude that the crust–mantle boundary (or Moho) is deeper than 80 kilometres.