29 research outputs found
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&
Enthesiale Veraenderungen (Entheseal changes), In: Neue Erkenntnisse zur frühmittelalterlichen Separatgrablege von Niederstotzingen, Kreis Heidenheim (New results from the cemetery of Niederstotzingen)
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
Health-related quality of life from the perspective of children with severe specific language impairment
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