New Formation Models for the Kepler-36 System Bodenheimer, Peter; Stevenson, David J.; Lissauer, Jack J. ...
Astrophysical journal/The Astrophysical journal,
12/2018, Letnik:
868, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Formation of the planets in the Kepler-36 system is modeled by detailed numerical simulations according to the core-nucleated accretion scenario. The standard model is updated to include the ...dissolution of accreting rocky planetesimals in the gaseous envelope of the planet, leading to substantial enrichment of the envelope mass in heavy elements and a non-uniform composition with depth. For Kepler-36 c, models involving in situ formation and models involving orbital migration are considered. The results are compared with standard formation models. The calculations include the formation (accretion) phase as well as the subsequent cooling phase, up to the age of Kepler-36 (7 Gyr). During the latter phase, mass loss induced by stellar XUV radiation is included. In all cases, the results fit the measured mass, 7.84 M⊕, and radius, 3.68 R⊕, of Kepler-36 c. Two parameters are varied to obtain these fits: the disk solid surface density at the formation location and the "efficiency" factor in the XUV mass-loss rate. The updated models are hotter and therefore less dense in the silicate portion of the planet and in the overlying layers of H/He, as compared with standard models. The lower densities mean that only about half as much H/He is needed to be accreted to fit the present-day mass and radius constraints. For Kepler-36 b, an updated in situ calculation shows that the entire H/He envelope is lost, early in the cooling phase, in agreement with observation.
Abstract
We perform long-term simulations, up to ten billion years, of closely spaced configurations of 2–6 planets, each as massive as the Earth, traveling on nested orbits about either stellar ...component in
α
Centauri AB. The innermost planet initially orbits at either the inner edge of its star’s empirical habitable zone (HZ) or the inner edge of its star’s conservative HZ. Although individual planets on low inclination, low eccentricity, orbits can survive throughout the HZs of both stars, perturbations from the companion star require that the minimum spacing of planets in multi-planet systems within the HZs of each star must be significantly larger than the spacing of similar multi-planet systems orbiting single stars in order to be long-lived. The binary companion induces a forced eccentricity upon the orbits of planets in orbit around either star. Planets on appropriately phased circumstellar orbits with initial eccentricities equal to their forced eccentricities can survive on more closely spaced orbits than those with initially circular orbits, although the required spacing remains higher than for planets orbiting single stars. A total of up to nine planets on nested prograde orbits can survive for the current age of the system within the empirical HZs of the two stars, with five of these orbiting
α
Centauri B and four orbiting
α
Centauri A.
We describe the catalogs assembled and the algorithms used to populate the revised TESS Input Catalog (TIC), based on the incorporation of the Gaia second data release. We also describe a revised ...ranking system for prioritizing stars for 2 minute cadence observations, and we assemble a revised Candidate Target List (CTL) using that ranking. The TIC is available on the Mikulski Archive for Space Telescopes server, and an enhanced CTL is available through the Filtergraph data visualization portal system at http://filtergraph.vanderbilt.edu/tess_ctl.
Changes in planetary obliquity, or axial tilt, influence the climates on Earth-like planets. In the solar system, the Earth's obliquity is stabilized by interactions with our moon, and the resulting ...small amplitude variations (∼2 4) are beneficial for advanced life. Most Sun-like stars have at least one stellar companion, and the habitability of circumstellar exoplanets is shaped by their stellar companion. We show that a stellar companion can dramatically change whether Earth-like obliquity stability is possible through planetary orbital precession relative to the binary orbit or resonant pumping of the obliquity through spin-orbit interactions. We present a new formalism for the planetary spin precession that accounts for orbital misalignments between the planet and binary. Using numerical modeling in Centauri AB, we show the following: there is a stark contrast between the planetary obliquity variations depending on the host star, planetary neighbors limit the possible spin states for Earth-like obliquity stability, and the presence of a moon can destabilize the obliquity, defying our Earth-based expectations. An Earth-like rotator orbiting the primary star would experience small obliquity variations for 87%, 74%, or 54% of solar-type binaries, depending on the mass of the primary (0.8, 1.0, or 1.2 M , respectively). Thus, Earth-like planets likely experience much larger obliquity variations, with more extreme climates, unless they are in specific states, such as orbiting nearly planar with the binary and rotating retrograde (backward) like Venus.
FORMATION AND STRUCTURE OF LOW-DENSITY EXO-NEPTUNES ROGERS, Leslie A; BODENHEIMER, Peter; LISSAUER, Jack J ...
Astrophysical journal/The Astrophysical journal,
09/2011, Letnik:
738, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Kepler has found hundreds of Neptune-size (2-6 R {circled plus}) planet candidates within 0.5 AU of their stars. The nature of the vast majority of these planets is not known because their masses ...have not been measured. Using theoretical models of planet formation, evolution, and structure, we explore the range of minimum plausible masses for low-density exo-Neptunes. We focus on highly irradiated planets with T eq >= 500 K. We consider two separate formation pathways for low-mass planets with voluminous atmospheres of light gases: core-nucleated accretion and outgassing of hydrogen from dissociated ices. We show that Neptune-size planets at T eq = 500 K with masses as small as a few times that of Earth can plausibly be formed by core-nucleated accretion coupled with subsequent inward migration. We also derive a limiting low-density mass-radius relation for rocky planets with outgassed hydrogen envelopes but no surface water. Rocky planets with outgassed hydrogen envelopes typically have computed radii well below 3 R {circled plus}. For both planets with H/He envelopes from core-nucleated accretion and planets with outgassed hydrogen envelopes, we employ planet interior models to map the range of planet mass-envelope mass-equilibrium temperature parameter space that is consistent with Neptune-size planet radii. Atmospheric mass loss mediates which corners of this parameter space are populated by actual planets and ultimately governs the minimum plausible mass at a specified transit radius. We find that Kepler's 2-6 R {circled plus} planet candidates at T eq = 500-1000 K could potentially have masses 4 M {circled plus}. Although our quantitative results depend on several assumptions, our qualitative finding that warm Neptune-size planets can have masses substantially smaller than those given by interpolating the masses and radii of planets within our Solar System is robust.
Abstract
Kepler-33 hosts five validated transiting planets ranging in period from 5 to 41 days. The planets are in nearly coplanar orbits and exhibit remarkably similar (appropriately scaled) transit ...durations indicative of similar impact parameters. The outer three planets have a radius of 3.5 ≲
R
p
/
R
⊕
≲ 4.7 and are closely packed dynamically, and thus transit timing variations can be observed. Photodynamical analysis of transit timing variations provide 2
σ
upper bounds on the eccentricity of the orbiting planets (ranging from <0.02 to <0.2) and the mean density of the host star (
0.39
−
0.02
+
0.01
g
cm
−
3
). We combine Gaia Early Data Release 3 parallax observations, the previously reported host-star effective temperature and metallicity, and our photodynamical model to refine properties of the host star and the transiting planets. Our analysis yields well-constrained masses for Kepler-33 e (
6.6
−
1.0
+
1.1
M
⊕
) and f (
8.2
−
1.2
+
1.6
M
⊕
) along with 2
σ
upper limits for planets c (<19
M
⊕
) and d (<8.2
M
⊕
). We confirm the reported low bulk densities of planet d (<0.4 g cm
−3
), e (0.8 ± 0.1 g cm
−3
), and f (0.7 ± 0.1 g cm
−3
). Based on comparisons with planetary evolution models, we find that Kepler-33 e and f exhibit relatively high envelope mass fractions of
f
env
=
7.0
−
0.5
+
0.6
%
and
f
env
= 10.3% ± 0.6%, respectively. Assuming a mass for planet d ∼4
M
⊕
suggests that it has
f
env
≳ 12%.
Advances in exoplanet science from Kepler Lissauer, Jack J; Dawson, Rebekah I; Tremaine, Scott
Nature (London),
2014-Sep-18, 2014-09-18, 20140918, Letnik:
513, Številka:
7518
Journal Article
Recenzirano
Numerous telescopes and techniques have been used to find and study extrasolar planets, but none has been more successful than NASA's Kepler space telescope. Kepler has discovered most of the known ...exoplanets, the smallest planets to orbit normal stars and the planets most likely to be similar to Earth. Most importantly, Kepler has provided us with our first look at the typical characteristics of planets and planetary systems for planets with sizes as small as, and orbits as large as, those of Earth.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT Kepler has discovered hundreds of systems with multiple transiting exoplanets which hold tremendous potential both individually and collectively for understanding the formation and evolution ...of planetary systems. Many of these systems consist of multiple small planets with periods less than ∼50 days known as Systems with Tightly spaced Inner Planets, or STIPs. One especially intriguing STIP, Kepler-80 (KOI-500), contains five transiting planets: f, d, e, b, and c with periods of 1.0, 3.1, 4.6, 7.1, and 9.5 days, respectively. We provide measurements of transit times and a transit timing variation (TTV) dynamical analysis. We find that TTVs cannot reliably detect eccentricities for this system, though mass estimates are not affected. Restricting the eccentricity to a reasonable range, we infer masses for the outer four planets (d, e, b, and c) to be , , , and Earth masses, respectively. The similar masses but different radii are consistent with terrestrial compositions for d and e and ∼2% H/He envelopes for b and c. We confirm that the outer four planets are in a rare dynamical configuration with four interconnected three-body resonances that are librating with few degree amplitudes. We present a formation model that can reproduce the observed configuration by starting with a multi-resonant chain and introducing dissipation. Overall, the information-rich Kepler-80 planets provide an important perspective into exoplanetary systems.
Numerical simulations, based on the core-nucleated accretion model, are presented for the formation of Jupiter at 5.2
AU in three primordial disks with three different assumed values of the surface ...density of solid particles. The grain opacities in the envelope of the protoplanet are computed using a detailed model that includes settling and coagulation of grains and that incorporates a recalculation of the grain size distribution at each point in time and space. We generally find lower opacities than the 2% of interstellar values used in previous calculations (Hubickyj, O., Bodenheimer, P., Lissauer, J.J. 2005. Icarus 179, 415–431; Lissauer, J.J., Hubickyj, O., D’Angelo, G., Bodenheimer, P. 2009. Icarus 199, 338–350). These lower opacities result in more rapid heat loss from and more rapid contraction of the protoplanetary envelope. For a given surface density of solids, the new calculations result in a substantial speedup in formation time as compared with those previous calculations. Formation times are calculated to be 1.0, 1.9, and 4.0
Myr, and solid core masses are found to be 16.8, 8.9, and 4.7
M
⊕, for solid surface densities,
σ, of 10, 6, and 4
g
cm
−2, respectively. For
σ
=
10 and
σ
=
6
g
cm
−2, respectively, these formation times are reduced by more than 50% and more than 80% compared with those in a previously published calculation with the old approximation to the opacity.
PDF
