206 research outputs found
Coorbital Satellites of Saturn: Congenital Formation
Saturn is the only known planet to have coorbital satellite systems. In the
present work we studied the process of mass accretion as a possible mechanism
for coorbital satellites formation. The system considered is composed of
Saturn, a proto-satellite and a cloud of planetesimals distributed in the
coorbital region around a triangular Lagrangian point. The adopted relative
mass for the proto-satellite was 10^-6 of Saturn's mass and for each
planetesimal of the cloud three cases of relative mass were considered, 10^-14,
10^-13 and 10^-12 masses of Saturn. In the simulations each cloud of
planetesimal was composed of 10^3, 5 x 10^3 or 10^4 planetesimals. The results
of the simulations show the formation of coorbital satellites with relative
masses of the same order of those found in the saturnian system (10^-13 -
10^-9). Most of them present horseshoe type orbits, but a significant part is
in tadpole orbit around L_4 or L_5. Therefore, the results indicate that this
is a plausible mechanism for the formation of coorbital satellites.Comment: 10 pages, 9 figures, 4 table
Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars
Models of terrestrial planet formation for our solar system have been
successful in producing planets with masses and orbits similar to those of
Venus and Earth. However, these models have generally failed to produce
Mars-sized objects around 1.5 AU. The body that is usually formed around Mars'
semimajor axis is, in general, much more massive than Mars. Only when Jupiter
and Saturn are assumed to have initially very eccentric orbits (e 0.1),
which seems fairly unlikely for the solar system, or alternately, if the
protoplanetary disk is truncated at 1.0 AU, simulations have been able to
produce Mars-like bodies in the correct location. In this paper, we examine an
alternative scenario for the formation of Mars in which a local depletion in
the density of the protosolar nebula results in a non-uniform formation of
planetary embryos and ultimately the formation of Mars-sized planets around 1.5
AU. We have carried out extensive numerical simulations of the formation of
terrestrial planets in such a disk for different scales of the local density
depletion, and for different orbital configurations of the giant planets. Our
simulations point to the possibility of the formation of Mars-sized bodies
around 1.5 AU, specifically when the scale of the disk local mass-depletion is
moderately high (50-75%) and Jupiter and Saturn are initially in their current
orbits. In these systems, Mars-analogs are formed from the protoplanetary
materials that originate in the regions of disk interior or exterior to the
local mass-depletion. Results also indicate that Earth-sized planets can form
around 1 AU with a substantial amount of water accreted via primitive
water-rich planetesimals and planetary embryos. We present the results of our
study and discuss their implications for the formation of terrestrial planets
in our solar system.Comment: Accepted for publication in The Astrophysical Journa
A Compound model for the origin of Earth's water
One of the most important subjects of debate in the formation of the solar
system is the origin of Earth's water. Comets have long been considered as the
most likely source of the delivery of water to Earth. However, elemental and
isotopic arguments suggest a very small contribution from these objects. Other
sources have also been proposed, among which, local adsorption of water vapor
onto dust grains in the primordial nebula and delivery through planetesimals
and planetary embryos have become more prominent. However, no sole source of
water provides a satisfactory explanation for Earth's water as a whole. In view
of that, using numerical simulations, we have developed a compound model
incorporating both the principal endogenous and exogenous theories, and
investigating their implications for terrestrial planet formation and
water-delivery. Comets are also considered in the final analysis, as it is
likely that at least some of Earth's water has cometary origin. We analyze our
results comparing two different water distribution models, and complement our
study using D/H ratio, finding possible relative contributions from each
source, focusing on planets formed in the habitable zone. We find that the
compound model play an important role by showing more advantage in the amount
and time of water-delivery in Earth-like planets.Comment: Accepted for publication in The Astrophysical Journa
Radiogenic power and geoneutrino luminosity of the Earth and other terrestrial bodies through time
We report the Earth's rate of radiogenic heat production and (anti)neutrino
luminosity from geologically relevant short-lived radionuclides (SLR) and
long-lived radionuclides (LLR) using decay constants from the geological
community, updated nuclear physics parameters, and calculations of the
spectra. We track the time evolution of the radiogenic power and luminosity of
the Earth over the last 4.57 billion years, assuming an absolute abundance for
the refractory elements in the silicate Earth and key volatile/refractory
element ratios (e.g., Fe/Al, K/U, and Rb/Sr) to set the abundance levels for
the moderately volatile elements. The relevant decays for the present-day heat
production in the Earth ( TW) are from K, Rb,
Sm, Th, U, and U. Given element concentrations
in kg-element/kg-rock and density in kg/m, a simplified equation to
calculate the present day heat production in a rock is: The
radiogenic heating rate of Earth-like material at Solar System formation was
some 10 to 10 times greater than present-day values, largely due to
decay of Al in the silicate fraction, which was the dominant radiogenic
heat source for the first Ma. Assuming instantaneous Earth formation,
the upper bound on radiogenic energy supplied by the most powerful short-lived
radionuclide Al ( = 0.7 Ma) is 5.510 J,
which is comparable (within a factor of a few) to the planet's gravitational
binding energy.Comment: 28 pages, 6 figures, 5 table
Oort cloud (exo)planets
Dynamical instabilities among giant planets are thought to be nearly
ubiquitous, and culminate in the ejection of one or more planets into
interstellar space. Here we perform N-body simulations of dynamical
instabilities while accounting for torques from the galactic tidal field. We
find that a fraction of planets that would otherwise have been ejected are
instead trapped on very wide orbits analogous to those of Oort cloud comets.
The fraction of ejected planets that are trapped ranges from 1-10%, depending
on the initial planetary mass distribution. The local galactic density has a
modest effect on the trapping efficiency and the orbital radii of trapped
planets. The majority of Oort cloud planets survive for Gyr timescales. Taking
into account the demographics of exoplanets, we estimate that one in every
200-3000 stars could host an Oort cloud planet. This value is likely an
overestimate, as we do not account for instabilities that take place at early
enough times to be affected by their host stars' birth cluster, or planet
stripping from passing stars. If the Solar System's dynamical instability
happened after birth cluster dissolution, there is a ~7% chance that an ice
giant was captured in the Sun's Oort cloud.Comment: MNRAS Letters, in press. Blog post about paper at
https://planetplanet.net/2023/06/21/oort-cloud-exoplanets
Born extra-eccentric: A broad spectrum of primordial configurations of the gas giants that match their present-day orbits
In a recent paper we proposed that the giant planets' primordial orbits may
have been eccentric (~0.05), and used a suite of dynamical simulations to show
outcomes of the giant planet instability that are consistent with their
present-day orbits. In this follow-up investigation, we present more
comprehensive simulations incorporating superior particle resolution, longer
integration times, and eliminating our prior means of artificially forcing
instabilities to occur at specified times by shifting a planets' position in
its orbit. While we find that the residual phase of planetary migration only
minimally alters the the planets' ultimate eccentricities, our work uncovers
several intriguing outcomes in realizations where Jupiter and Saturn are born
with extremely large eccentricities (~0.10 and ~0.25, respectively). In
successful simulations, the planets' orbits damp through interactions with the
planetesimal disk prior to the instability, thus loosely replicating the
initial conditions considered in our previous work. Our results therefore
suggest an even wider range of plausible evolutionary pathways are capable of
replicating Jupiter and Saturn's modern orbital architecture.Comment: 12 pages, 3 figures, 2 tables, accepted for publication in Icaru
Formation of Super-Earths
Super-Earths are the most abundant planets known to date and are
characterized by having sizes between that of Earth and Neptune, typical
orbital periods of less than 100 days and gaseous envelopes that are often
massive enough to significantly contribute to the planet's overall radius.
Furthermore, super-Earths regularly appear in tightly-packed multiple-planet
systems, but resonant configurations in such systems are rare. This chapters
summarizes current super-Earth formation theories. It starts from the formation
of rocky cores and subsequent accretion of gaseous envelopes. We follow the
thermal evolution of newly formed super-Earths and discuss their atmospheric
mass loss due to disk dispersal, photoevaporation, core-cooling and collisions.
We conclude with a comparison of observations and theoretical predictions,
highlighting that even super-Earths that appear as barren rocky cores today
likely formed with primordial hydrogen and helium envelopes and discuss some
paths forward for the future.Comment: Invited review accepted for publication in the 'Handbook of
Exoplanets,' Planet Formation section, Springer Reference Works, Juan Antonio
Belmonte and Hans Deeg, Ed
- …