Seminar: Spring 2008. Meeting time: Mondays 11:30am - 12:15am
Subject: Astronomy today.
We will discuss recent exciting papers published on astro-ph. We will also review papers, which are related with research projects of our students.
Candidate papers:
0802.0001
Little Dwarf Galaxies survive within Bigger Dwarfs: Why Some Dwarfs Go Dark and Others Stay Luminous
George Lake, Elena D'Onghia
The Large Magellanic Cloud (LMC) was the largest galaxy in a group of galaxies that entered the Milky Way (MW) system at late times. Seven of the 11 brightest dwarf galaxies of the MW may have been part of this system. The association of dwarfs with the plane of the LMCs orbit has been used to argue that they are formed from tidal debris from LMC and SMC (Kroupa et al 2005). Instead, we find that they owe to the tidal breakup of the Magellanic Group. The Cold Dark Matter (CDM) paradigm suffers from the small-scale structure problem where 500 galaxies as massive as Draco and Ursa Minor are expected, but only 11 are seen. If seven of the 11 observed were part of the LMC group, the substructure in this group is close to CDM predictions. There are other likely nearby dwarf groups, including a second Milky Way group associated with Fornax (Lynden-Bell 1982), great circles of satellites in M31 (Koch & Grebel 2006) and groupings of otherwise isolated dwarfs (Tully et al. 2006). For the first time, we build he circular velocity distribution of the satellites in system as small as groups of dwarf galaxies, using the dwarf galaxies that likely entered with the LMC system and data on nearby dwarf systems. Our work points to natural mechanisms that lead to less suppression of satellites in dwarf groups providing an explanation for the missing satellite problem in the Local Group.
[12] arXiv:0802.0046 [ps, pdf, other]
X-ray emission from O stars
David H. Cohen (Swarthmore College)
Comments: 9 pages; color figures. To appear in IAU Symposium 250, "Massive Stars as Cosmic Engines," Kauai, HI, December 2007; eds. Bresolin, Crowther, & Puls, Cambridge University Press, 2008. The paper posted here has one additional figure (Fig. 6). A b/w version (sans extra figure) is available at this http URL
Subjects: Astrophysics (astro-ph)
Young O stars are strong, hard, and variable X-ray sources, properties which strongly affect their circumstellar and galactic environments. After ~1 Myr, these stars settle down to become steady sources of soft X-rays. I use high-resolution X-ray spectroscopy and MHD modeling to show that young O stars like theta-1 Ori C are well explained by the magnetically channeled wind shock scenario. After their magnetic fields dissipate, older O stars produce X-rays via shock heating in their unstable stellar winds. Here too I use X-ray spectroscopy and numerical modeling to confirm this scenario. In addition to elucidating the nature and cause of the O star X-ray emission, modeling of the high-resolution X-ray spectra of O supergiants provides strong evidence that mass-loss rates of these O stars have been overestimated.
Population III Star Formation and IMF
Michael L. Norman
We review recent 3D cosmological hydrodynamic simulations of primordial star formation from cosmological initial conditions (Pop III.1) and from initial conditions that have been altered by radiative feedback from stellar sources (Pop III.2). We concentrate on simulations that resolve the formation of the gravitationally unstable cloud cores in mini-halos over the mass range $10^5 < M/\Msun < 10^7 $ and follow their evolution to densities of at least $10^{10} \cmm3$ and length scales of $<10^{-2}$ pc such that accretion rates can be estimated. The advent of ensembles of such simulations exploring a variety of conditions permits us to assess the robustness of the standard model for Pop III.1 star formation and investigate scatter in their formation redshifts and accretion rates, thereby providing much needed information about the Pop III IMF. The simulations confirm the prediction that Pop III.1 stars were massive ($\sim 100 \Msun$), and form in isolation in primordial mini-halos. Simulations of Pop III.2 star forming in relic HII regions suggest somewhat lower masses ($\sim 30 \Msun$) which may help explain the chemical abundances of extremely metal poor stars. We note that no 3D simulation at present has achieved stellar density let alone followed the entire accretion history of the star in any scenario, and thus the IMF of Pop III stars remains poorly determined theoretically.
Comments: 13 pages, 16 figures, To appear in "Proceedings of First Stars III," Eds. Brian W. O'Shea, Alexander Heger & Tom Abel, AIP Conference Series
Cite as: arXiv:0801.4924v1 [astro-ph]
Simulating the Gaseous Halos of Galaxies
Tobias Kaufmann, James S. Bullock, Ari Maller, Taotao Fang 28 Jan 2008) 0801.4046
Observations of local X-ray absorbers, high-velocity clouds, and distant quasar absorption line systems suggest that a significant fraction of baryons may reside in multi-phase, low-density, extended, ~100 kpc, gaseous halos around normal galaxies. We present a pair of high-resolution SPH (smoothed particle hydrodynamics) simulations that explore the nature of cool gas infall into galaxies, and the physical conditions necessary to support the type of gaseous halos that seem to be required by observations. The two simulations are identical other than their initial gas density distributions: one is initialized with a standard hot gas halo that traces the cuspy profile of the dark matter, and the other is initialized with a cored hot halo with a high central entropy, as might be expected in models with early pre-heating feedback. Galaxy formation proceeds in dramatically different fashions in these two cases. While the standard cuspy halo cools rapidly, primarily from the central region, the cored halo is quasi-stable for ~4 Gyr and eventually cools via the fragmentation and infall of clouds from ~100 kpc distances. After 10 Gyr of cooling, the standard halo's X-ray luminosity is ~100 times current limits and the resultant disk galaxy is twice as massive as the Milky Way. In contrast, the cored halo has an X-ray luminosity that is in line with observations, an extended cloud population reminiscent of the high-velocity cloud population of the Milky Way, and a disk galaxy with half the mass and ~50% more specific angular momentum than the disk formed in the low-entropy simulation. These results suggest that the distribution and character of halo gas provides an important testing ground for galaxy formation models and may be used to constrain the physics of galaxy formation.
The Formation of Polar Disk Galaxies
Chris B. Brook, Fabio Governato, Thomas Quinn, James Wadsley, Alyson M. Brooks, Beth Willman, Adrienne Stilp, Patrik Jonsson
Polar Ring Galaxies, such as NGC4650A, are a class of galaxy which have two kinematically distinct components that are inclined by almost 90 degrees to each other. These striking galaxies challenge our understanding of how galaxies form; the origin of their distinct components has remained uncertain, and the subject of much debate. We use high-resolution cosmological simulations of galaxy formation to show that Polar Ring Galaxies are simply an extreme example of the angular moment misalignment that occurs during the hierarchical structure formation characteristic of Cold Dark Matter cosmology. In our model, Polar Ring Galaxies form through the continuous accretion of gas whose angular momentum is misaligned with the central galaxy.
arXiv:0802.1051v3
Are retrograde resonances possible in multi-planet systems?
Julie Gayon, Eric Bois (Nice Sophia-Antipolis University, CNRS, Observatoire de la Cote d'Azur, Laboratoire Cassiopee, France)
Most multi-planetary systems are characterized by hot-Jupiters close to their central star, moving on eccentric orbits. From a dynamical point of view, compact multi-planetary systems form a specific class of the general N-body problem (where N>3). Moreover, extrasolar planets are found in prograde orbits about their host star, and often in mean motion resonances (MMR). In a first step, we study theoretically a new stabilizing mechanism suitable for compact two-planet systems. This mechanism involves counter-revolving orbits forming a retrograde MMR. In a second step, we investigate the feasibility of planetary systems hosting counter-revolving planets. Dynamical stability, observations, and formation processes of these systems are analyzed and discussed. To characterize the dynamical behavior of multi-dimensional planetary systems, we apply our technique of global dynamics analysis based on the MEGNO indicator (Mean Exponential Growth factor of Nearby Orbits) that provides the fine structure of the phase space. In a few cases of possible counter-revolving configurations, we carry out new fits to the observations using the Pikaia genetic algorithm. A statistical study of the stability in the neighborhood of different observed, planetary-systems is completed using a Monte-Carlo method. We analyse the observational data for the HD73526 planetary system and find that counter-revolving configurations may be consistent with the observational data. We highlight the fine and characteristic structure of retrograde MMRs. We demonstrate that retrograde resonances open a family of stabilizing mechanisms involving new apsidal precession behaviors. Considering two possible formation mechanisms (free-floating planet and Slingshot model), we conclude that counter-revolving configurations are feasible.
arXiv:0801.1089v3 [astro-ph]
Toward a Deterministic Model of Planetary Formation V. Accumulation Near the Ice Line and Emergence of Short-Period Earths
Shigeru Ida, D. N. C. Lin
We address two outstanding issues in the sequential accretion scenario for gas giant planet formation, the retention of dust grains in the presence of gas drag and that of cores despite type I migration. Theoretical models suggest that planets form in protostellar disk regions with an inactive neutral ``dead zone'' near the mid plane, sandwiched together by partially ionized surface layers where magnetorotational instability is active. Due to a transition in the abundance of dust grains, the active layer's thickness decreases abruptly near the ice line, which leads to local surface density and pressure distribution maxima near the ice line. This barrier locally retains protoplanetary cores and enhances the heavy element surface density to the critical value needed to initiate efficient gas accretion. We simulate and reproduce the observed frequency and mass-period distribution of gas giants around solar type stars without having to greatly reduce the type I migration strength. We also predict slightly smaller populations of Earth-mass planets in the habitable zone and close to their host stars.
arXiv:0802.1114v1
The High Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy
Authors: William F. Zech, Nicolas Lehner, J. Christopher Howk, W. Van Dyke Dixon, Thomas M. Brown
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS E140M) observations of the post-asymptotic giant branch star ZNG 1 in the globular cluster Messier 5 (l=3.9, b=+47.7; d=7.5 kpc, z=+5.3 kpc). High velocity absorption is seen in C IV, Si IV, O VI, and lower ionization species at LSR velocities of -140 and -110 km/s. We conclude that this gas is not circumstellar on the basis of photoionization models and path length arguments. Thus, the high velocity gas along the ZNG 1 sight line is the first evidence that highly-ionized HVCs can be found near the Galactic disk. We measure the metallicity of these HVCs to be [O/H]=+0.22\pm0.10, the highest of any known HVC. Given the clouds' metallicity and distance constraints, we conclude that these HVCs have a Galactic origin. This sight line probes gas toward the inner Galaxy, and we discuss the possibility that these HVCs may be related to a Galactic nuclear wind or Galactic fountain circulation in the inner regions of the Milky Way.arXiv:0802.0286v1 [astro-ph]
A ~5 M_earth Super-Earth Orbiting GJ 436?: The Power of Near-Grazing Transits
Ignasi Ribas (ICE/CSIC-IEEC, Spain), Andreu Font-Ribera (ICE/CSIC-IEEC, Spain), Jean-Philippe Beaulieu (IAP, France)
Most of the presently identified exoplanets have masses similar to that of Jupiter and therefore are assumed to be gaseous objects. With the ever-increasing interest in discovering lower-mass planets, several of the so-called super-Earths (i.e., with masses in the interval 1 M_earth < M < 10 M_earth), which are predicted to be rocky, have already been found. Here we report the possible discovery of a planet around the M-type star GJ 436 with a minimum mass of 4.8+/-0.6 M_earth and a true mass of ~5 M_earth, which makes it the least massive planet around a main-sequence star found to date. In contrast with other discoveries, the planet is identified from its perturbations on an inner Neptune-mass transiting planet (GJ 436b), by pumping eccentricity and producing secular variations in the orbital inclination. Analysis of published radial velocity measurements indeed reveals a significant signal corresponding to an orbital period that is very close to the 2:1 mean motion resonance with the inner planet. The near-grazing nature of the transit makes it extremely sensitive to small changes in the inclination. Such method holds great potential to push the detection limits of present and planned space missions to lower mass planets than those responsible for the transit.
arXiv:0801.3230v1
Sequestration of ethane in the cryovolcanic subsurface of Titan
Olivier Mousis, Bernard Schmitt
Saturn's largest satellite, Titan, has a thick atmosphere dominated by nitrogen and methane. The dense orange-brown smog hiding the satellite's surface is produced by photochemical reactions of methane, nitrogen and their dissociation products with solar ultraviolet, which lead primarily to the formation of ethane and heavier hydrocarbons. In the years prior to the exploration of Titan's surface by the Cassini-Huygens spacecraft, the production and condensation of ethane was expected to have formed a satellite-wide ocean one kilometer in depth, assuming that it was generated over the Solar system's lifetime. However, Cassini-Huygens observations failed to find any evidence of such an ocean. Here we describe the main cause of the ethane deficiency on Titan: cryovolcanic lavas regularly cover its surface, leading to the percolation of the liquid hydrocarbons through this porous material and its accumulation in subsurface layers built up during successive methane outgassing events. The liquid stored in the pores may, combined with the ice layers, form a stable ethane-rich clathrate reservoir, potentially isolated from the surface. Even with a low open porosity of 10% for the subsurface layers, a cryovolcanic icy crust less than 2300 m thick is required to bury all the liquid hydrocarbons generated over the Solar system's lifetime.
arXiv:0802.1033v1
Confirmation of the remarkable compactness of massive quiescent galaxies at z~2.3: early-type galaxies did not form in a simple monolithic collapse
Pieter van Dokkum, Marijn Franx, Mariska Kriek, Bradford Holden, Garth Illingworth, Daniel Magee, Rychard Bouwens, Danilo Marchesini, Ryan Quadri, Greg Rudnick, Edward Taylor, Sune Toft
Using deep near-infrared spectroscopy Kriek et al. (2006) found that ~45% of massive galaxies at z~2.3 have evolved stellar populations and little or no ongoing star formation. Here we determine the sizes of these quiescent galaxies using deep, high-resolution images obtained with HST/NIC2 and laser guide star-assisted Keck/AO. Considering that their median stellar mass is 1.7x10^11 Solar masses the galaxies are remarkably small, with a median effective radius of 0.9 kpc. Galaxies of similar mass in the nearby Universe have sizes of ~5 kpc and average stellar densities which are two orders of magnitude lower than the z~2.3 galaxies. These results extend earlier work at z~1.5 and confirm previous studies at z>2 which lacked spectroscopic redshifts and imaging of sufficient resolution to resolve the galaxies. Our findings demonstrate that fully assembled early-type galaxies make up at most ~10% of the population of K-selected quiescent galaxies at z~2.3, effectively ruling out simple monolithic models for their formation. The galaxies must evolve significantly after z~2.3, through dry mergers or other processes, consistent with predictions from hierarchical models.
arXiv:0802.4094v1
A Spitzer study of star-forming regions in Virgo Cluster galaxies
O. Ivy Wong et al.
Abstract: We present a preliminary study of the star formation distribution
within three Virgo Cluster galaxies using the 24 micron Spitzer observations
from the Spitzer Survey of Virgo (SPITSOV) in combination with H-alpha
observations. The purpose of our study is to explore the relationship
between the star formation distribution within galaxies and the type (and
phase) of interactions experienced within the cluster environment. Neither
highly-obscured star formation nor strongly enhanced star-forming regions
along the leading edges of galaxies experiencing ICM-ISM interactions were
found. However, very unobscured star-forming regions were found in the outer
parts of one galaxy (NGC 4402), while relatively obscured star-forming
regions were found in the extraplanar regions of another galaxy (NGC 4522).
We attribute the observed differences between NGC 4402 and NGC 4522 to the
direction of motion of each galaxy through the ICM.
Star cluster stability and the effects of binary stars: Galactic open clusters
R. de Grijs, S. P. Goodwin, M. B. N. Kouwenhoven, P. Kroupa
The diagnostic age versus mass-to-light ratio diagram is often used in attempts to constrain the shape of the stellar initial mass function (IMF), and the stability and the potential longevity of extragalactic young to intermediate-age massive star clusters. Here, we explore its potential for Galactic open clusters. On the basis of a homogenised cluster sample we provide useful constraints on the dynamical state of the individual clusters, and also on the presence of significant binary fractions. Using the massive young Galactic cluster Westerlund 1 as a key example, we caution that stochasticity in the IMF introduces significant additional uncertainties. Therefore, the stability and long-term survival chances of Westerlund 1 remain largely inconclusive. We conclude that for an open cluster to survive for any significant length of time and in the absence of substantial external perturbations, it is a necessary but not a sufficient condition to be located close to or (in the presence of a significant binary population) somewhat BELOW the predicted photometric evolutionary sequences for "normal" simple stellar populations (although such a location may be dominated by a remaining "bound" cluster core and thus not adequately reflect the overall cluster dynamics). arXiv:0803.1991v1
The Chemical Evolution of Dwarf Spheroidal Galaxies: Dissecting the Inner Regions and their Stellar Populations
A. Marcolini (1), A. D'Ercole (2), G. Battaglia (3;4), B.K. Gibson
Using 3-dimensional hydrodynamical simulations of isolated dwarf spheroidal galaxies (dSphs), we undertake an analysis of the chemical properties of their inner regions, identifying the respective roles played by Type Ia (SNe Ia) and Type II (SNe II) supernovae. The effect of inhomogeneous pollution from SNe Ia is shown to be prominent within two core radii, with the stars forming therein amounting to ~20% of the total. These stars are relatively iron-rich and alpha-element-depleted compared to the stars forming in the rest of the galaxy. At odds with the projected stellar velocity dispersion radial profile, the actual 3-dimensional one shows a depression in the central region, where the most metal-rich (ie. [Fe/H]-rich) stars are partly segregated. This naturally results in two different stellar populations, with an anti-correlation between [Fe/H] and velocity dispersion, in the same sense as that observed in the Sculptor and Fornax dSphs. Because the most iron-rich stars in our model are also the most alpha-depleted, a natural prediction and test of our model is that the same radial segregation effects should exist between
arXiv:0803.0385v1
The Stellar Initial Mass Function in 2007: A Year for Discovering Variations
Bruce G. Elmegreen (IBM, T.J. Watson Research Center)
The characteristic mass M_c and slope Gamma of the IMF are reviewed for clusters, field regions, galaxies, and regions formed during cosmological times. Local star formation has a somewhat uniform M_c and Gamma. Statistical variations in Gamma are summarized, as are the limitations imposed by these variations. Cosmological star formation appears to have both a higher M_c and a slightly shallower slope at intermediate to high stellar mass. The center of the Milky Way may have a shallow slope too. Field regions have slightly steeper slopes than clusters, but this could be the result of enhanced drift of low mass stars out of clusters and associations. Dwarf galaxies also have steeper slopes. Results from the observation of pre-stellar clumps are reviewed too. Pre-stellar clumps appear to have about the same mass function as stars and are therefore thought to be the main precursors to stars. If this is the case, then the IMF is generally determined by gas-phase processes. Brown dwarf formation also shares many characteristics of star formation, suggesting that they form by similar mechanisms.
arXiv:0803.3154v1
Formation and Detectability of Terrestrial Planets Around Alpha Centauri B
Javiera M. Guedes, Eugenio J. Rivera, Erica Davis, Gregory Laughlin, Elisa V. Quintana, Debra A. Fischer
(Submitted on 25 Feb 2008 (v1), last revised 17 Mar 2008 (this version, v3))
We simulate the formation of planetary systems around Alpha Centauri B. The N-body accretionary evolution of a 1/r disk populated with 400-900 lunar-mass protoplanets is followed for 200 Myr. All simulations lead to the formation of multiple-planet systems with at least one planet in the 1-2 MEarth mass range at 0.5-1.5 AU. We examine the detectability of our simulated planetary systems by generating synthetic radial velocity observations including noise based on the radial velocity residuals to the recently published three planet fit to the nearby K0V star HD 69830. Using these synthetic observations, we find that we can reliably detect a 1.8 MEarth planet in the habitable zone of Alpha Centauri B after only three years of high cadence observations. We also find that the planet is detectable even if the radial velocity precision is 3 m/s, as long as the noise spectrum is white. Our results show that the greatest uncertainty in our ability to detect rocky planets in the Alpha Centauri system is the unknown magnitude of ultra-low frequency stellar noise.
arXiv:0802.3482v3
Chandra unveils a binary Active Galactic Nucleus in Mrk463
Stefano Bianchi, Marco Chiaberge, Enrico Piconcelli, Matteo Guainazzi, Giorgio Matt
(Submitted on 6 Feb 2008)
We analyse Chandra, XMM-Newton and HST data of the double-nucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk463. The Chandra detection of two luminous ($\mathrm{L}_\mathrm{2-10 keV}=1.5\times10^{43}$ and $3.8\times10^{42}$ erg cm$^{-2}$ s$^{-1}$), unresolved nuclei in Mrk~463 indicates that this galaxy hosts a binary AGN, with a projected separation of $\simeq3.8$ kpc ($3.83\pm0.01$ arcsec). While the East nucleus was already known to be a Seyfert 2 (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk463 is therefore the clearest case so far for a binary AGN, after NGC6240.
Comments: 7 pages, 7 figures, accepted for publication in MNRAS
arXiv:0802.0825v1 [astro-ph]
Study of the Surface of 2003 EL61: the largest carbon-depleted object in the trans-neptunian belt
N. Pinilla-ALonso, R. Brunetto, J. Licandro, R. Gil-Hutton, T.L. Roush, G. Strazzulla
2003 EL61 is the largest member of a group of TNOs with similar orbits and 'unique' spectra (neutral slope in the visible and the deepest water ice absorption bands ever observed in the TNb). Studying the composition of the surface of 2003 EL61 provides useful constrains on the origin of this particular group of TNOs and on the outer Solar system's history.
We present visible and near-infrared spectra of 2003 EL61 obtained with the 4.2m WHT and the 3.6m TNG at the Roque de los Muchachos Observatory (Canary Islands, Spain). Near infrared spectra were obtained at different rotational phases covering almost one complete rotational period. Spectra are fitted using Hapke scattering models and constraints on the surface composition are derived.
No significant variations in the spectral slope and in the depth of the water ice absorption bands at different rotational phases are evident, suggesting that the surface of 2003 EL61 is homogeneous. The scattering models show that a 1:1 intimate mixture of crystalline and amorphous water ice is the most probable composition for the surface of this TNO, and constrain the presence of other minor constituents to a maximum of 8%
The derived composition suggests that: a) cryovolcanism is unlikely to be the main resurfacing process responsible for the high presence of water ice on the surface of these bodies; b) the surface is older than 10^8 yr. Any catastrophic event, like the collision suggested to be the origin of this population, had to happen at least 10^8 yr ago; c) the surface of 2003 EL61 is depleted of carbon chains. According to the orbital parameters of this population, this makes it a possible source of carbon-depleted Jupiter family comets.
Comments: 9 pages, 7 graphs. Keywords: water ice, carbon-depleted, Kuiper Belt, astrochemistry, spectroscopy
Cite as: arXiv:0803.1080v1
Constraints on the angular distribution of satellite galaxies about spiral hosts
Jason H. Steffen (Fermilab) Octavio Valenzuela (UNAM, Mexico)
(Submitted on 14 Dec 2007 (v1), last revised 11 Apr 2008 (this version, v2))
We present, using a novel technique, a study of the angular distribution of satellite galaxies around a sample of isolated, blue host galaxies selected from the sixth data release of the Sloan Digital Sky Survey. As a complement to previous studies we subdivide the sample of galaxies into bins of differing inclination and use the systematic differences that would exist between the different bins as the basis for our approach. We parameterize the cumulative distribution function of satellite galaxies and apply a maximum likelihood, Monte-Carlo technique to determine allowable distributions, which we show as an exclusion plot. We find that the allowed distributions of the satellites of spiral hosts are very nearly isotropic. We outline our formalism and our analysis and discuss how this technique may be refined for future studies and future surveys.
Comments: MNRAS in press. Version 2 has some sections reordered and additional discussion included
Subjects: Astrophysics (astro-ph)
Report number: FERMILAB-PUB-07-654-A-CD
Cite as: arXiv:0712.2363v2
On the Dynamical Stability of the Solar System
Konstantin Batygin, Gregory Laughlin
(Submitted on 11 Apr 2008)
A long-term numerical integration of the classical Newtonian approximation to the planetary orbital motions of the full Solar System (sun + 8 planets), spanning 20 Gyr, was performed. The results showed no severe instability arising over this time interval. Subsequently, utilizing a bifurcation method described by Jacques Laskar, two numerical experiments were performed with the goal of determining dynamically allowed evolutions for the Solar System in which the planetary orbits become unstable. The experiments yielded one evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and another in which Mercury and Venus collide in ~862Myr. In the latter solution, as a result of Mercury's unstable behavior, Mars was ejected from the Solar System at ~822Myr. We have performed a number of numerical tests that confirm these results, and indicate that they are not numerical artifacts. Using synthetic secular perturbation theory, we find that Mercury is destabilized via an entrance into a linear secular resonance with Jupiter in which their corresponding eigenfrequencies experience extended periods of commensurability. The effects of general relativity on the dynamical stability are discussed. An application of the bifurcation method to the outer Solar System (Jupiter, Saturn, Uranus, and Neptune) showed no sign of instability during the course of 24Gyr of integrations, in keeping with an expected Uranian dynamical lifetime of 10^(18) years.
Cite as: arXiv:0804.1946v1 [astro-ph]