Observed glacier and volatile distribution on Pluto from atmosphere–topography processes
Nature 540, 7631 (2016). doi:10.1038/nature19337
Authors: Tanguy Bertrand & François Forget
Pluto has a variety of surface frosts and landforms as well as a complex atmosphere. There is ongoing geological activity related to the massive Sputnik Planitia glacier, mostly made of nitrogen (N2) ice mixed with solid carbon monoxide and methane, covering the 4-kilometre-deep, 1,000-kilometre-wide basin of Sputnik Planitia near the anti-Charon point. The glacier has been suggested to arise from a source region connected to the deep interior, or from a sink collecting the volatiles released planetwide. Thin deposits of N2 frost, however, were also detected at mid-northern latitudes and methane ice was observed to cover most of Pluto except for the darker, frost-free equatorial regions. Here we report numerical simulations of the evolution of N2, methane and carbon monoxide on Pluto over thousands of years. The model predicts N2 ice accumulation in the deepest low-latitude basin and the threefold increase in atmospheric pressure that has been observed to occur since 1988. This points to atmospheric–topographic processes as the origin of Sputnik Planitia’s N2 glacier. The same simulations also reproduce the observed quantities of volatiles in the atmosphere and show frosts of methane, and sometimes N2, that seasonally cover the mid- and high latitudes, explaining the bright northern polar cap reported in the 1990s and the observed ice distribution in 2015. The model also predicts that most of these seasonal frosts should disappear in the next decade.
Astronomy: A black hole changes its feeding habits
Nature 540, 7631 (2016). doi:10.1038/nature20480
Authors: Stephanie LaMassa
In the 1980s, the gas surrounding a black hole in a nearby galaxy began to emit much more radiation than before. This change has unexpectedly reversed in the past five years, questioning our understanding of these extreme phenomena.
Planetary science: Pluto's telltale heart
Nature 540, 7631 (2016). doi:10.1038/540042a
Authors: Amy C. Barr
Studies of a large frost-filled basin on Pluto show that this feature altered the dwarf planet's spin axis, driving tectonic activity on its surface, and hint at the presence of a subsurface ocean. See Letters p.86, p.90, p.94 & p.97
Corrigendum: Slowly fading super-luminous supernovae that are not pair-instability explosions
Nature 539, 7630 (2016). doi:10.1038/nature19850
Authors: M. Nicholl, S. J. Smartt, A. Jerkstrand, C. Inserra, M. McCrum, R. Kotak, M. Fraser, D. Wright, T.-W. Chen, K. Smith, D. R. Young, S. A. Sim, S. Valenti, D. A. Howell, F. Bresolin, R. P. Kudritzki, J. L. Tonry, M. E. Huber, A. Rest, A. Pastorello, L. Tomasella, E. Cappellaro, S. Benetti, S. Mattila, E. Kankare, T. Kangas, G. Leloudas, J. Sollerman, F. Taddia, E. Berger, R. Chornock, G. Narayan, C. W. Stubbs, R. J. Foley, R. Lunnan, A. Soderberg, N. Sanders, D. Milisavljevic, R. Margutti, R. P. Kirshner, N. Elias-Rosa, A. Morales-Garoffolo, S. Taubenberger, M. T. Botticella, S. Gezari, Y. Urata, S. Rodney, A. G. Riess, D. Scolnic, W. M. Wood-Vasey, W. S. Burgett, K. Chambers, H. A. Flewelling, E. A. Magnier, N. Kaiser, N. Metcalfe, J. Morgan, P. A. Price, W. Sweeney & C. Waters
Nature502, 346–349 (2013); doi:10.1038/nature12569In this Letter, we have identified an important error affecting Fig. 4 and Extended Data Fig. 6, as well as the values of some parameters derived from our model fits. We stress that
Magnetic reversals from planetary dynamo waves
Nature 539, 7630 (2016). doi:10.1038/nature19842
Authors: Andrey Sheyko, Christopher C. Finlay & Andrew Jackson
A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth’s magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes place in Earth’s core, but the precise mechanism is debated. The majority of numerical geodynamo simulations that exhibit reversals operate in a regime in which the viscosity of the fluid remains important, and in which the dynamo mechanism primarily involves stretching and twisting of field lines by columnar convection. Here we present an example of another class of reversing-geodynamo model, which operates in a regime of comparatively low viscosity and high magnetic diffusivity. This class does not fit into the paradigm of reversal regimes that are dictated by the value of the local Rossby number (the ratio of advection to Coriolis force). Instead, stretching of the magnetic field by a strong shear in the east–west flow near the imaginary cylinder just touching the inner core and parallel to the axis of rotation is crucial to the reversal mechanism in our models, which involves a process akin to kinematic dynamo waves. Because our results are relevant in a regime of low viscosity and high magnetic diffusivity, and with geophysically appropriate boundary conditions, this form of dynamo wave may also be involved in geomagnetic reversals.
History: Women who read the stars
Nature 539, 7630 (2016). doi:10.1038/539491a
Author: Sue Nelson
Sue Nelson delights in Dava Sobel's account of a rare band of human computers.
Astrophysics: Homing in on a fast radio burst
Nature 539, 7630 (2016). doi:10.1038/539470b
The origins of powerful, millisecond-long radio pulses from space called fast radio bursts (FRBs) remain a mystery. But researchers studying the brightest FRB seen so far have zeroed in on its location more accurately than ever before.Vikram Ravi at the California Institute of Technology