101,086 research outputs found
Evolution of planetary interiors
No full textThe Encyclopedia of the Solar System, third edition provides a framework for understanding the origin and evolution of the solar system, historical discoveries, and details about planetary bodies and how they interact—with an astounding breadth of content and breathtaking visual impact. The encyclopedia includes the latest explorations and observations, hundreds of color digital images and illustrations, and over 1,000 pages. It stands alone as the definitive work in this field, and will serve as a modern messenger of scientific discovery and provide a look into the future of our solar system.
New additions to the third edition will reflect the latest progress and growth in the field, including past and present space missions to the terrestrial planets, the outer solar systems and space telescopes used to detect extrasolar planets
Equilibrium Spacetime Correlations of the Toda Lattice on the Hydrodynamic Scale
No full textWe report on molecular dynamics simulations of spacetime correlations of the Toda lattice in thermal equilibrium. The correlations of stretch, momentum, and energy are computed numerically over a wide range of pressure and temperature. Our numerical results are compared with the predictions from linearized generalized hydrodynamics on the Euler scale. The system size is N = 3000, 4000 and time t = 600, at which ballistic scaling is well confirmed. With no adjustable parameters, the numerically obtained scaling functions agree with the theory within a precision of less than 3.5%
Geology, life and habitability
No full textThe examination of contemporary systems and the rock record has demonstrated that the biosphere and geosphere are intimately linked, presumably since life's origin. The geosphere provides trace and essential nutrients for life, sources of reduced compounds and electron acceptors, that is, the energy for life to occur, and habitats ranging from ‘simple’ surfaces to grow on to unique endolithic environments formed at least in part by the microorganisms themselves. The hydrosphere is perhaps more important than the lithosphere, because it provides the solvent necessary for biogeochemical reactions and life to occur. The major question about how life originated cannot be readily answered; however, the question of habitability is relatively easy. Using Earth as our role model, there are several candidate extrasolar bodies within our solar system, for example, Mars and Europa, that could support life
Overview
No full texta symmetry operator. This approach has been used not only to find solutions, but to gain some insight into the reason why in the Kerr background, components can be decoupled and then the decoupled equations subsequently solved by separation of variables. The underlying feature was found to be a Killing-Yano tensor [Y52], or equivalently a two-index Killing spinor [WP70]. This work then lead to the extension of these solutions to a much larger class of backgrounds (including all vacuum Petrov type-D spacetimes). The conditions that allow the use of scalar potentials in this way appear to be quite special to the 4D Lorentzian setting, and so it is not surprising that most authors use either the Newman-Penrose or twocomponent spinor formalisms, which are optimised for this case. Generalisations of Killings equations appear in the theory of separation of variables in a more general setting and so recasting the Debye potential formalism and symmetry operators so derived in a way not notat
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Planetary Heat Flow measurements and thermal disturbances caused by lander shadowing
No full textThe planetary heat flow is one of the fundamental quantities describing the thermal state of a planet. It influences the tectonic and volcanic processes we see at the surface and is closely connected to the planet’s geodynamic activity. It largely determines subsurface temperatures and provides one of the few constraints we have for thermal evolution models [1][2].
Upcoming lander missions will conduct in situ geophysical experiments and measure the planetary heat flow of Mars. The first such measurement is scheduled for ESA’s ExoMars
mission, which will deliver a geophysical instrument package to the martian surface. This will include the Heat Flow and Physical Properties Package (HP3) [3], a heat flowprobe which will access the martian subsurface to a depth of 5 m and perform measurements of the soils thermophysical parameters and temperatures as a function of depth.
Here we will investigate how soil shadowing by the lander structure influences the subsurface soil temperatures and derive requirements of how meaningful measurements of the subsurface thermal gradient can be performed. Particular attention will be paid to the differences between short and long term measurements and measurements underneath and outside the lander structure.
[1] Breuer, D., and Spohn, T. (2003), J. Geophys. Res., 108, 81.
[2] Hauck II, S.A., and Phillips, R.J. (2002), J. Geophys. Res., 107, 61.
[3] Spohn, T., et al. (2001), Planet. Space Sci., 49, 1415, 15711577.<br /
Comet 67P/Churyumov-Gerasimenko: Hardening of the subsurface layer
No full textFrom the operation of the MUPUS thermal probe Spohn et al. (2015) concluded that the material of the nucleus of 67P/Churyumov–Gerasimenko is likely to have a high strength, at least locally at the Philae landing site. In this work we consider the derived strength of the material in order to constrain its granulation. For this purpose we performed numerical simulations of the long-term sintering of ice–dust granular mixtures of different granulation, covered by a dust mantle. The dust mantle has a thickness of 0–16 cm, and a (pore size and temperature-dependent) thermal conductivity. According to our simulations a hardened layer at least a meter thick forms beneath the dust only when the grains are tens of microns in radius, or smaller
Counterfactuals and two kinds of ought
No full textI discuss Caspar Hare’s solution to a new variant of Parfit’s Non-Identity Problem. Hare’s solution rests on distinguishing two kinds of ought: The Ought of Omniscient Desire: what you oughtOD to do is what an omniscient, rational creature with appropriate interests would want you to do. The Ought of Most Reason: what you oughtMR to do is what there is most reason to do. I argue that the distinction does not dissolve the problem. Moreover, I show that Hare’s proposal to spell out his distinction in terms of an embedded counterfactual (if you had not done what you did, then, if you had done what you did, what would the consequence have been?) is flawed
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