Binary star to spill celestial secrets
Nature 512, 7512 (2014). http://www.nature.com/doifinder/10.1038/512013a
Author: Alexandra Witze
Close approach and violent interaction of stars in η Carinae system will provide rare insight into stellar enigma.
Astronomers using NASA's Hubble Space Telescope have unexpectedly discovered the most distant cosmic magnifying glass yet, produced by a monster elliptical galaxy. The galaxy, seen here as it looked 9.6 billion years ago, is so massive that its gravity bends, magnifies, and distorts light from objects behind it, a phenomenon called gravitational lensing. In the Hubble image, the galaxy is the red object in the enlarged view at left.
The tidal–rotational shape of the Moon and evidence for polar wander
Nature 512, 7513 (2014). doi:10.1038/nature13639
Authors: Ian Garrick-Bethell, Viranga Perera, Francis Nimmo & Maria T. Zuber
The origin of the Moon’s large-scale topography is important for understanding lunar geology, lunar orbital evolution and the Moon’s orientation in the sky. Previous hypotheses for its origin have included late accretion events, large impacts, tidal effects and convection processes. However, testing these hypotheses and quantifying the Moon’s topography is complicated by the large basins that have formed since the crust crystallized. Here we estimate the large-scale lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the spherical harmonic degree-2 topography is consistent with a crust-building process controlled by early tidal heating throughout the Moon. The remainder of the degree-2 topography is consistent with a frozen tidal–rotational bulge that formed later, at a semi-major axis of about 32 Earth radii. The probability of the degree-2 shape having both tidal-heating and frozen shape characteristics by chance is less than 1%. We also infer that internal density contrasts eventually reoriented the Moon’s polar axis by 36 ± 4°, to the configuration we observe today. Together, these results link the geology of the near and far sides, and resolve long-standing questions about the Moon’s large-scale shape, gravity and history of polar wander.
Misaligned protoplanetary disks in a young binary star system
Nature 511, 7511 (2014). doi:10.1038/nature13521
Authors: Eric L. N. Jensen & Rachel Akeson
Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star’s equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet’s orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process.
Following the extensive in-orbit commissioning review and after encountering the unexpected challenges highlighted previously on the blog, Gaia is now ready to begin its science mission.
Read the announcement published today on the ESA Portal: Gaia: 'Go' for science
And for a full quantitative analysis of Gaia’s expected science performance based on the results of commissioning, see: Commissioning review: Gaia ready to start routine operations