Small particles dominate Saturn’s Phoebe ring to surprisingly large distances
Nature 522, 7555 (2015). doi:10.1038/nature14476
Authors: Douglas P. Hamilton, Michael F. Skrutskie, Anne J. Verbiscer & Frank J. Masci
Saturn’s faint outermost ring, discovered in 2009 (ref. 1), is probably formed by particles ejected from the distant moon Phoebe. The ring was detected between distances of 128 and 207 Saturn radii (RS = 60,330 kilometres) from the planet, with a full vertical extent of 40RS, making it well over ten times larger than Saturn’s hitherto largest known ring, the E ring. The total radial extent of the Phoebe ring could not, however, be determined at that time, nor could particle sizes be significantly constrained. Here we report infrared imaging of the entire ring, which extends from 100RS out to a surprisingly distant 270RS. We model the orbital dynamics of ring particles launched from Phoebe, and construct theoretical power-law profiles of the particle size distribution. We find that very steep profiles fit the data best, and that elevated grain temperatures, arising because of the radiative inefficiency of the smallest grains, probably contribute to the steepness. By converting our constraint on particle sizes into a form that is independent of the uncertain size distribution, we determine that particles with radii greater than ten centimetres, whose orbits do not decay appreciably inward over 4.5 billion years, contribute at most about ten per cent to the cross-sectional area of the ring’s dusty component.
Astronomy: Megaflare seen on star surface
Nature 522, 7555 (2015). doi:10.1038/522131d
Astronomers have spotted an enormous surge of light and magnetic energy on a nearby star.A team led by Wouter Vlemmings at Chalmers University of Technology near Gothenburg, Sweden, pointed the ALMA radio telescope in northern Chile at the red giant Mira A, a star
We recently reported the discovery of an unpublished manuscript by Albert Einstein in which he attempted a 'steady-state' model of the universe, i.e., a cosmic model in which the expanding universe remains essentially unchanged due to a continuous formation of matter from empty space. The manuscript was apparently written in early 1931, many years before the steady-state models of Fred Hoyle, Hermann Bondi and Thomas Gold. We compare Einstein's steady-state cosmology with that of Hoyle, Bondi and Gold and consider the reasons Einstein abandoned his model. The relevance of steady-state models for today's cosmology is briefly reviewed.
Two of the most reliable changes in the sky are the daily rising of the sun in the east and setting of the sun in the west. But if you lived on a couple of Pluto's moons you wouldn't know when the day would begin, or even what direction the sun would rise. That's because, unlike Earth's moon, at least two of Pluto's small moons, Hydra and Nix, are tumbling chaotically through space. Why? Because they orbit inside a dynamically shifting gravitational field caused by the system's two central bodies, Pluto and Charon, that are whirling around each other. The moons are also football shaped, and this contributes to the chaotic rotation.
Resonant interactions and chaotic rotation of Pluto’s small moons
Nature 522, 7554 (2015). doi:10.1038/nature14469
Authors: M. R. Showalter & D. P. Hamilton
Four small moons—Styx, Nix, Kerberos and Hydra—follow near-circular, near-equatorial orbits around the central ‘binary planet’ comprising Pluto and its large moon, Charon. New observational details of the system have emerged following the discoveries of Kerberos and Styx. Here we report that Styx, Nix and Hydra
Astronomy: Pluto leads the way in planet formation
Nature 522, 7554 (2015). doi:10.1038/522040a
Authors: Scott J. Kenyon
Images from the Hubble Space Telescope cast new light on the orbits, shapes and sizes of Pluto's small satellites. The analysis comes just before a planned reconnaissance by the first spacecraft to visit them. See Article p.45
Hawaii prunes Mauna Kea telescope hub
Nature 522, 7554 (2015). http://www.nature.com/doifinder/10.1038/522015a
Author: Alexandra Witze
Cultural fight over sacred mountain accelerates observatory closures.