Impact inducted surface heating by planetesimals on early Mars

We investigate the influence of impacts of large planetesimals and small planetary embryos on the early Martian surface on the hydrodynamic escape of an early steam atmosphere that is exposed to the high soft X-ray and EUV flux of the young Sun. Impact statistics in terms of number, masses, velocities, and angles of asteroid impacts onto the early Mars are determined via n-body integrations. Based on these statistics, smoothed particle hydrodynamics (SPH) simulations result in estimates of energy transfer into the planetary surface material and according surface heating. For the estimation of the atmospheric escape rates we applied a soft X-ray and EUV absorption model and a 1-D upper atmosphere hydrodynamic model to a magma ocean-related catastrophically outgassed steam atmosphere with surface pressure values of 52 bar H2O and 11 bar CO2. The estimated impact rates and energy deposition onto an early Martian surface can account for substantial heating. The energy influx and conversion rate into internal energy is most likely sufficient to keep a shallow magma ocean liquid for an extended period of time. Higher surface temperatures keep the outgassed steam atmosphere longer in vapor form and therefore enhance its escape to space within about 0.6 Myr after its formation.Comment: submitted to A&

How initial and boundary conditions affect protoplanetary migration in a turbulent sub-Keplerian accretion disc: 2D non viscous SPH simulations

Current theories on planetary formation establish that giant planet formation should be contextual to their quick migration towards the central star due to the protoplanets-disc interactions on a timescale of the order of $10^5$ years, for objects of nearly 10 terrestrial masses. Such a timescale should be smaller by an order of magnitude than that of gas accretion onto the protoplanet during the hierarchical growing-up of protoplanets by collisions with other minor objects. These arguments have recently been analysed using N-body and/or fluid-dynamics codes or a mixing of them. In this work, inviscid 2D simulations are performed, using the SPH method, to study the migration of one protoplanet, to evaluate the effectiveness of the accretion disc in the protoplanet dragging towards the central star, as a function of the mass of the planet itself, of disc tangential kinematics. To this purpose, the SPH scheme is considered suitable to study the roles of turbulence, kinematic and boundary conditions, due to its intrinsic advective turbulence, especially in 2D and in 3D codes. Simulations are performed both in disc sub-Keplerian and in Keplerian kinematic conditions as a parameter study of protoplanetary migration if moderate and consistent deviations from Keplerian Kinematics occur. Our results show migration times of a few orbital periods for Earth-like planets in sub-Keplerian conditions, while for Jupiter-like planets estimates give that about $10^4$ orbital periods are needed to half the orbital size. Timescales of planet migration are strongly dependent on the relative position of the planet with respect to the shock region near the centrifugal barrier of the disc flow.Comment: 12 pages, 18 figures, under review by MNRA

A comparative study of disc-planet interaction

We perform numerical simulations of a disc-planet system using various grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run for a simple setup where Jupiter and Neptune mass planets on a circular orbit open a gap in a protoplanetary disc during a few hundred orbital periods. We compare the surface density contours, potential vorticity and smoothed radial profiles at several times. The disc mass and gravitational torque time evolution are analyzed with high temporal resolution. There is overall consistency between the codes. The density profiles agree within about 5% for the Eulerian simulations while the SPH results predict the correct shape of the gap although have less resolution in the low density regions and weaker planetary wakes. The disc masses after 200 orbital periods agree within 10%. The spread is larger in the tidal torques acting on the planet which agree within a factor 2 at the end of the simulation. In the Neptune case the dispersion in the torques is greater than for Jupiter, possibly owing to the contribution from the not completely cleared region close to the planet.Comment: 32 pages, accepted for publication in MNRA

Black hole spin: theory and observation

In the standard paradigm, astrophysical black holes can be described solely by their mass and angular momentum - commonly referred to as `spin' - resulting from the process of their birth and subsequent growth via accretion. Whilst the mass has a standard Newtonian interpretation, the spin does not, with the effect of non-zero spin leaving an indelible imprint on the space-time closest to the black hole. As a consequence of relativistic frame-dragging, particle orbits are affected both in terms of stability and precession, which impacts on the emission characteristics of accreting black holes both stellar mass in black hole binaries (BHBs) and supermassive in active galactic nuclei (AGN). Over the last 30 years, techniques have been developed that take into account these changes to estimate the spin which can then be used to understand the birth and growth of black holes and potentially the powering of powerful jets. In this chapter we provide a broad overview of both the theoretical effects of spin, the means by which it can be estimated and the results of ongoing campaigns.Comment: 55 pages, 5 figures. Published in: "Astrophysics of Black Holes - From fundamental aspects to latest developments", Ed. Cosimo Bambi, Springer: Astrophysics and Space Science Library. Additional corrections mad

The viscous gas ring as an astrophysical test problem for a viscous SPH-code

We present the general analytic solution of a viscous gas ring around a central mass. This solution is used to test a further development of the smoothed particle hydrodynamics (SPH) algorithm, which is capable of simulating problems with physical viscosity (here: with kinematic viscosity). We discuss some SPH simulation results and conclude some fundamental properties of the algorithm. 1 Introduction A large class of problems in theoretical astrophysics is related to the dynamics of compressible flows including many physical effects such as gravity, radiation, viscosity, electric charges and currents, or magnetic fields. These problems are attacked primarily through numerical simulations, and different numerical methods for various aspects of astrophysical gas dynamics have been developed in the past or are currently in the state of development. These algorithms have to be tested in order to verify their stability, accuracy, and robustness. An ideal test is, of course, a comparison ..

The viscous gas ring as an astrophysical test problem for a viscous SPH-code

We present the general analytic solution of a viscous gas ring around a central mass. This solution is used to test a further development of the smoothed particle hydrodynamics (SPH) algorithm, which is capable of simulating problems with physical viscosity (here: with kinematic viscosity). We discuss some SPH simulation results and conclude some fundamental properties of the algorithm. c # 1999 Elsevier Science B.V. All rights reserved. Keywords: Numerical hydrodynamics; Particle methods; SPH benchmark problem 1. Introduction A large class of problems in theoretical astrophysics is related to the dynamics of compressible #ows including many physical e#ects such as gravity, radiation, viscosity, electric charges and currents, or magnetic #elds. These problems are attacked primarily through numerical simulations, and di#erent numerical methods for various aspects of astrophysical gas dynamics have been developed in the past or are currently in the state of development. These algori..

Distributed Implementation of SPH for Simulations of Accretion Disks

two steps. These ODEs are subsequently integrated numerically using standard methods. First the field quantities f(r) are smoothed, i. e., they are replaced by the convolution f(r) \Gamma! Z f(r 0 ) W (jr \Gamma r 0 j; h) dV 0 (1) with a differentiable kernel W which is normalised to unity. The smoothing length h is a measure of the (compact) support of the kernel function, and it follows f(r) = Z f(r 0 ) W (jr \Gamma r 0 j; h) dV 0 +O(h 2 ) : (2) A common choice for the kernel is a cubic spline (see, e. g., Monagha

Parallel SPH on Cray T3E and NEC SX-4 using DTS

. In this paper we report on the results of a joint effort of astrophysicists and computer scientists to develop and implement a parallel program that enables us to solve large systems of hydrodynamic equations and covers a wide range of applications in astrophysics. We introduce the Distributed Threads System (DTS) as an environment for the development of portable parallel applications. The numerical method Smoothed Particle Hydrodynamics (SPH) is used to simulate the viscous spreading of an accretion disk around a massive compact object as an astrophysical test problem. The SPH code was parallelized using DTS and successfully ported to systems of different architecture. The use of a parallel SPH code on supercomputers enables us to treat astrophysical systems that were not accessible before. The achieved speedup proves the efficiency of DTS as a parallel programming environment. The physical results show the consistency and accuracy of the SPH method. 1 Introduction The numerical s..