58 research outputs found
Structure and Evolution of Internally Heated Hot Jupiters
Hot Jupiters receive strong stellar irradiation, producing equilibrium
temperatures of . Incoming irradiation directly
heats just their thin outer layer, down to pressures of $\sim 0.1 \
\mathrm{bars}1 - 10 \ \mathrm{bars}\gtrsim 10\%100 \ \mathrm{bars}1\%1.4 R_{\rm Jup}10^4 \ \mathrm{bars}\approx 99\%$ of the planet's mass -- suppresses planetary cooling
as effectively as heating at the center. In summary, we find that relatively
shallow heating is required to explain the radii of most hot Jupiters, provided
that this heat is applied early and persists throughout their evolution.Comment: Accepted at ApJ, 14 pages, 10 figure
On the Formation of Planetesimals via Secular Gravitational Instabilities with Turbulent Stirring
We study the gravitational instability (GI) of small solids in a gas disk as
a mechanism to form planetesimals. Dissipation from gas drag introduces secular
GI, which proceeds even when standard GI criteria for a critical density or
Toomre's predict stability. We include the stabilizing effects of turbulent
diffusion, which suppresses small scale GI. The radially wide rings that do
collapse contain up to Earth masses of solids. Subsequent
fragmentation of the ring (not modeled here) would produce a clan of chemically
homogenous planetesimals. Particle radial drift time scales (and, to a lesser
extent, disk lifetimes and sizes) restrict the viability of secular GI to disks
with weak turbulent diffusion, characterized by . Thus
midplane dead zones are a preferred environment. Large solids with radii
cm collapse most rapidly because they partially decouple from the
gas disk. Smaller solids, even below mm-sizes could collapse if
particle-driven turbulence is weakened by either localized pressure maxima or
super-Solar metallicity. Comparison with simulations that include particle
clumping by the streaming instability shows that our linear model underpredicts
rapid, small scale gravitational collapse. Thus the inclusion of more detailed
gas dynamics promotes the formation of planetesimals. We discuss relevant
constraints from Solar System and accretion disk observations.Comment: Accepted for publication in the Astrophysical Journal; 20 pages, 10
figure
Evidence for universality in the initial planetesimal mass function
Planetesimals may form from the gravitational collapse of dense particle
clumps initiated by the streaming instability. We use simulations of
aerodynamically coupled gas-particle mixtures to investigate whether the
properties of planetesimals formed in this way depend upon the sizes of the
particles that participate in the instability. Based on three high resolution
simulations that span a range of dimensionless stopping time no statistically significant differences in the initial
planetesimal mass function are found. The mass functions are fit by a
power-law, , with and
errors of . Comparing the particle density fields prior
to collapse, we find that the high wavenumber power spectra are similarly
indistinguishable, though the large-scale geometry of structures induced via
the streaming instability is significantly different between all three cases.
We interpret the results as evidence for a near-universal slope to the mass
function, arising from the small-scale structure of streaming-induced
turbulence.Comment: 7 pages, 4 figures, accepted to ApJ Letters after minor
modifications, including two new figures and some new text that better
clarify our result
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