12 research outputs found
Planetesimal formation at the gas pressure bump following a migrating planet I. Basic characteristics of the new formation model
To avoid known difficulties in planetesimal formation such as the drift or
fragmentation barriers, many scenarios have been proposed. However, in these
scenarios, planetesimals form in general only at some specific locations in
protoplanetary discs. On the other hand, it is generally assumed in planet
formation models and population synthesis models, that planetesimals are
broadly distributed in the protoplanetary disc. Here we propose a new scenario
in which planetesimals can form in broad areas of the discs. Planetesimals form
at the gas pressure bump formed by a first-generation planet (e.g. formed by
pebble accretion) and the formation region spreads inward in the disc as the
planet migrates. We use a simple 1D Lagrangian particle model to calculate the
radial distribution of pebbles in the gas disc perturbed by a migrating
embedded planet. We consider that planetesimals form by streaming instability
at the points where the pebble-to-gas density ratio on the mid-plane becomes
larger than unity. We also study the effect of some key parameters like the
ones of the gas disc model, the pebble mass flux, the migration speed of the
planet, and the strength of turbulence. We find that planetesimals form in wide
areas of the discs provided the flux of pebbles is typical and the turbulence
is not too strong. The planetesimal surface density depends on the pebble mass
flux and the migration speed of the planet. The total mass of the planetesimals
and the orbital position of the formation area depend strongly on the pebble
mass flux. We also find that the profile of the planetesimal surface density
and its slope can be estimated by very simple equations. We show that our new
scenario can explain the formation of planetesimals in broad areas. The simple
estimates we provide for the planetesimal surface density profile can be used
as initial conditions for population synthesis models.Comment: 12 pages, 9 figures, 1 table, accepted for publication in Astronomy &
Astrophysic
Possibility of Concentration of Non-volatile Species near the Surface of Comet 67P/Churyumov-Gerasimenko
The cometary materials are thought to be the reservoir of primitive materials
in the Solar System. The recent detection of glycine and CHNH by the
ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that
amino acids and their precursors may have been formed in an early evolutionary
phase of the Solar System. We investigate the evolution of cometary interior
considering the evaporation process of water followed by the concentration of
non-volatile species. We develop a Simplified Cometary Concentration Model
(SCCM) to simulate the evaporation and concentration processes on the cometary
surface.We use 67P/Churyumov-Gerasimenko as the benchmark of SCCM. We
investigate the depth of the layer where non-volatile species concentrate after
the numerous passages of perihelion after the formation of the Solar System. As
a result, the SCCM explains the observed production rates of water and
CHNH at 100 comet years. SCCM results suggest that the non-volatile
species would concentrate at depths between 0 and 100cm of comet surface within
10 comet years. Our results also suggest that the non-volatile species would
concentrate several meters beneath the surface before it hit the early Earth.
This specific mass of non-volatile species may provide unique chemical
condition to the volcanic hot spring pools.Comment: accepted to A&
Photophoresis in the circumjovian disk and its impact on the orbital configuration of the Galilean satellites
Jupiter has four large regular satellites called the Galilean satellites: Io, Europa, Ganymede, and Callisto. The inner three of the Galilean satellites orbit in a 4:2:1 mean motion resonance; therefore their orbital configuration may originate from the stopping of the migration of Io near the bump in the surface density distribution and following resonant trapping of Europa and Ganymede. The formation mechanism of the bump near the orbit of the innermost satellite, Io, is not yet understood, however. Here, we show that photophoresis in the circumjovian disk could be the cause of the bump using analytic calculations of steady-state accretion disks. We propose that photophoresis in the circumjovian disk could stop the inward migration of dust particles near the orbit of Io. The resulting dust-depleted inner region would have a higher ionization fraction, and thus admit increased magnetorotational-instability-driven accretion stress in comparison to the outer region. The increase of the accretion stress at the photophoretic dust barrier would form a bump in the surface density distribution, halting the migration of Io