# Posts Tagged solar system

## Recent Postings from solar system

### H2O abundances in the atmospheres of three hot Jupiters

The core accretion theory for giant planet formation predicts enrichment of elemental abundances in planetary envelopes caused by runaway accretion of planetesimals, which is consistent with measured super-solar abundances of C, N, P, S, Xe, and Ar in Jupiter’s atmosphere. However, the abundance of O which is expected to be the most dominant constituent of planetesimals is unknown for solar system giant planets, owing to the condensation of water in their ultra-cold atmospheres, thereby posing a key unknown in solar system formation. On the other hand, hundreds of extrasolar hot Jupiters are known with very high temperatures (>~1000 K) making them excellent targets to measure H2O abundances and, hence, oxygen in their atmospheres. We constrain the atmospheric H2O abundances in three hot Jupiters (HD 189733b, HD 209458b, and WASP-12b), spanning a wide temperature range (1200-2500 K), using their near-infrared transmission spectra obtained using the HST WFC3 instrument. We report conclusive measurements of H2O in HD 189733b and HD 209458b, while that in WASP-12b is not well constrained by present data. The data allow nearly solar as well as significantly sub-solar abundances in HD 189733b and WASP-12b. However, for HD 209458b, we report the most precise H2O measurement in an exoplanet to date that suggests a ~20-135 sub-solar H2O abundance. We discuss the implications of our results on the formation conditions of hot Jupiters and on the likelihood of clouds in their atmospheres. Our results highlight the critical importance of high-precision spectra of hot Jupiters for deriving their H2O abundances.

### A Pilot Search for Evidence of Extrasolar Earth-analog Plate Tectonics

Relative to calcium, both strontium and barium are markedly enriched in Earth’s continental crust compared to the basaltic crusts of other differentiated rocky bodies within the solar system. Here, we both re-examine available archived Keck spectra to place upper bounds on n(Ba)/n(Ca) and revisit published results for n(Sr)/n(Ca) in two white dwarfs that have accreted rocky planetesimals. We find that at most only a small fraction of the pollution is from crustal material that has experienced the distinctive elemental enhancements induced by Earth-analog plate tectonics. In view of the intense theoretical interest in the physical structure of extrasolar rocky planets, this search should be extended to additional targets.

### The inner solar system cratering record and the evolution of impactor populations

We review previously published and newly obtained crater size-frequency distributions in the inner solar system. These data indicate that the Moon and the terrestrial planets have been bombarded by two populations of objects. Population 1, dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced the heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. Population 2, dominating since about 3.8-3.7 Ga, has the same size distribution as near-Earth objects (NEOs), had a much lower impact flux, and produced a crater size distribution characterized by a differential -3 single-slope power law in the crater diameter range 0.02 km to 100 km. Taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. The NEO population is the source of Population 2 and it has been in near-steady state over the past ~3.7-3.8 gigayears; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. However, Population 1 were main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during giant planet orbit migration; this caused the so-called Late Heavy Bombardment (LHB). The LHB began some time before ~3.9 Ga, peaked and declined rapidly over the next ~100 to 300 megayears, and possibly more slowly from about 3.8-3.7 Ga to ~2 Ga. A third crater population (Population S) consists of secondary impact craters that can dominate the cratering record at small diameters.

### Meteoroid impacts onto asteroids: a competitor for Yarkovsky and YORP

<Abridged> The impact of a meteoroid onto an asteroid transfers linear and angular momentum to the larger body, which may affect its orbit and its rotational state. Here we show that the meteoroid environment of our Solar System can have an effect on small asteroids that is comparable to the Yarkovsky and Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effects under certain conditions. The momentum content of the meteoroids themselves is expected to generate an effect much smaller than that of the Yarkovsky effect. However, momentum transport by ejecta may increase the net effective force by two orders of magnitude for impacts into bare rock surfaces. This result is sensitive to the extrapolation of laboratory microcratering experiment results to real meteoroid-asteroid collisions and needs further study. If this extrapolation holds, then meteoroid impacts are more important to the dynamics of small asteroids than had previously been considered.

### Constraining the Cratering Chronology of Vesta

Vesta has a complex cratering history, with ancient terrains as well as recent large impacts that have led to regional resurfacing. Crater counts can help constrain the relative ages of different units on Vesta’s surface, but converting those crater counts to absolute ages requires a chronology function. We present a cratering chronology based on the best current models for the dynamical evolution of asteroid belt, and calibrate it to Vesta using the record of large craters on its surface. While uncertainties remain, our chronology function is broadly consistent with an ancient surface of Vesta as well as other constraints such as the bombardment history of the rest of the inner Solar System and the Ar-Ar age distribution of howardite, eucrite and diogenite (HED) meteorites from Vesta.

### Water Delivery and Giant Impacts in the 'Grand Tack' Scenario

A new model for terrestrial planet formation (Hansen 2009, Walsh et al. 2011) has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al. tested a possible mechanism to truncate the disk–a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies–the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as `primitive’ bodies). We find here that the planets will accrete on order 1-2% of their total mass from primitive planetesimals scattered onto planet-crossing orbits during the formation of the planets. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. While the radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system, we find that the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. However, 5 of the 27 planets larger than half an Earth mass formed in all simulations do experience large late impacts and subsequent accretion consistent with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event.

### The InfraRed Imaging Spectrograph (IRIS) for TMT: Overview of innovative science programs

IRIS (InfraRed Imaging Spectrograph) is a first light near-infrared diffraction limited imager and integral field spectrograph being designed for the future Thirty Meter Telescope (TMT). IRIS is optimized to perform astronomical studies across a significant fraction of cosmic time, from our Solar System to distant newly formed galaxies (Barton et al. [1]). We present a selection of the innovative science cases that are unique to IRIS in the era of upcoming space and ground-based telescopes. We focus on integral field spectroscopy of directly imaged exoplanet atmospheres, probing fundamental physics in the Galactic Center, measuring 10^4 to 10^10 Msun supermassive black hole masses, resolved spectroscopy of young star-forming galaxies (1 < z < 5) and first light galaxies (6 < z < 12), and resolved spectroscopy of strong gravitational lensed sources to measure dark matter substructure. For each of these science cases we use the IRIS simulator (Wright et al. [2], Do et al. [3]) to explore IRIS capabilities. To highlight the unique IRIS capabilities, we also update the point and resolved source sensitivities for the integral field spectrograph (IFS) in all five broadband filters (Z, Y, J, H, K) for the finest spatial scale of 0.004" per spaxel. We briefly discuss future development plans for the data reduction pipeline and quicklook software for the IRIS instrument suite.

### A Nonminimal Coupling Model and its Short-Range Solar System Impact

The objective of this work is to present the effects of a nonminimally coupled model of gravity on a Solar System short range regime. For this reason, this study is only valid when the cosmological contribution is considered irrelevant. The action functional of the model involves two functions $f^1(R)$ and $f^2(R)$ of the Ricci scalar curvature $R$, where the last one multiplies the matter Lagrangian. Using a Taylor expansion around $R=0$ for both functions $f^1(R)$ and $f^2(R)$, it was found that the metric around a spherical object is a perturbation of the weak-field Schwarzschild metric. The $tt$ component of the metric, a Newtonian plus a Yukawa perturbation term, is constrained using the available observational results. First it is shown that this effect is null when the characteristic mass scales of each function $f^1(R)$ and $f^2(R)$ are identical. Besides, the conclusion is that the nonminimal coupling only affects the Yukawa contribution strength and not its range and that the Starobinsky model for inflation is not experimentally constrained. Moreover, the geodetic precession effect, obtained also from the radial perturbation of the metric, reveals to be of no relevance for the constraints.

### MOST light-curve analysis of the gamma Dor pulsator HR 8799, showing resonances and amplitude variations

Context: The central star of the HR 8799 system is a gamma Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not known accurately, because the estimation depends strongly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR 8799. We organized an extensive photometric and multi-site spectroscopic observing campaign for studying the pulsations of the central star. Aims: The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47-d-long nearly continuous photometry obtained with the MOST space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite of an asteroseismic age determination. Methods: We carried out Fourier analysis of the wide-band photometric time series. Results: We find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f1 = 1.978 c/d. Many multiples of one ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f1, where n={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17, 18}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47-d time-scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars.

### Nitrogen isotopic fractionation during abiotic synthesis of organic solid particles

The formation of organic compounds is generally assumed to result from abiotic processes in the Solar System, with the exception of biogenic organics on Earth. Nitrogen-bearing organics are of particular interest, notably for prebiotic perspectives but also for overall comprehension of organic formation in the young solar system and in planetary atmospheres. We have investigated abiotic synthesis of organics upon plasma discharge, with special attention to N isotope fractionation. Organic aerosols were synthesized from N2-CH4 and N2-CO gaseous mixtures using low-pressure plasma discharge experiments, aimed at simulating chemistry occurring in Titan s atmosphere and in the protosolar nebula, respectively. Nitrogen is efficiently incorporated into the synthesized solids, independently of the oxidation degree, of the N2 content of the starting gas mixture, and of the nitrogen speciation in the aerosols. The aerosols are depleted in 15N by 15-25 permil relative to the initial N2 gas, whatever the experimental setup is. Such an isotopic fractionation is attributed to mass-dependent kinetic effect(s). Nitrogen isotope fractionation upon electric discharge cannot account for the large N isotope variations observed among solar system objects and reservoirs. Extreme N isotope signatures in the solar system are more likely the result of self-shielding during N2 photodissociation, exotic effect during photodissociation of N2 and/or low temperature ion-molecule isotope exchange. Kinetic N isotope fractionation may play a significant role in the Titan s atmosphere. We also suggest that the low delta15N values of Archaean organic matter are partly the result of abiotic synthesis of organics that occurred at that time.

### Chemical modeling of exoplanet atmospheres

The past twenty years have revealed the diversity of planets that exist in the Universe. It turned out that most of exoplanets are different from the planets of our Solar System and thus, everything about them needs to be explored. Thanks to current observational technologies, we are able to determine some information about the atmospheric composition, the thermal structure and the dynamics of these exoplanets, but many questions remain still unanswered. To improve our knowledge about exoplanetary systems, more accurate observations are needed and that is why the Exoplanet Characterisation Observatory (EChO) is an essential space mission. Thanks to its large spectral coverage and high spectral resolution, EChO will provide exoplanetary spectra with an unprecedented accuracy, allowing to improve our understanding of exoplanets. In this work, we review what has been done to date concerning the chemical modeling of exoplanet atmospheres and what are the main characteristics of warm exoplanet atmospheres, which are one of the main targets of EChO. Finally we will present the ongoing developments that are necessary for the chemical modeling of exoplanet atmospheres.

### Spins of Asteroids: The tale of the long tail

The Asteroid Belt and the Kuiper Belt are relics from the formation of our solar system. Understanding the size and spin distribution of the two belts is crucial for a deeper understanding of the formation of our solar system and the dynamical process that govern it. In this paper, we investigate the effect of collisions on the evolution of the spin distribution of asteroids and KBO’s. We find that the power law nature of the impactors’ size distribution leads to a L\’evy distribution of the spin rates. This results in a power law tail of the spin distribution, in stark contrast to the usually quoted Maxwellian distribution. We show that for bodies larger than 10 km, collisions alone lead to spin rates peaking at 0.15-0.5 revolutions per day. Comparing that to the observed spin rates of large asteroids ($R>50$ km), we find that the spins of large asteroids, peaking at $\sim1-2$ revolutions per day, are dominated by a primordial component that reflects the formation mechanism of the asteroids. Similarly, the Kuiper Belt has undergone virtually no collisional spin evolution, leading to less than 0.01 revolutions per day and that the observed spin rates of KBO’s are also primordial in nature.

### Gravitationally quantized orbits in the solar system: computations based on the global polytropic model

The so-called "global polytropic model" is based on the assumption of hydrostatic equilibrium for the solar system, or for a planet’s system of statellites (like the jovian system), described by the Lane-Emden differential equation. A polytropic sphere of polytropic index $n$ and radius $R_1$ represents the central component $S_1$ (Sun or planet) of a polytropic configuration with further components the polytropic spherical shells $S_2$, $S_3$, …, defined by the pairs of radii $(R_1,\,R_2)$, $(R_2,\,R_3)$, …, respectively. $R_1,\,R_2,\,R_3,\, \dots$, are the roots of the real part $\mathrm{Re}(\theta)$ of the complex Lane-Emden function $\theta$. Each polytropic shell is assumed to be an appropriate place for a planet, or a planet’s satellite, to be "born" and "live". This scenario has been studied numerically for the cases of the solar and the jovian systems. In the present paper, the Lane-Emden differential equation is solved numerically in the complex plane by using the Fortran code DCRKF54 (modified Runge-Kutta-Fehlberg code of fourth and fifth order for solving initial value problems in the complex plane along complex paths). We include in our numerical study some trans-Neptunian objects.

### Low Delta-V Near-Earth Asteroids: a survey of suitable targets for space missions

In the last decades Near-Earth Objects (NEOs) have become very important targets to study, since they can give us clues to the formation, evolution and composition of the Solar System. In addition, they may represent either a threat to humankind, or a repository of extraterrestrial resources for suitable space-borne missions. Within this framework, the choice of next-generation mission targets and the characterisation of a potential threat to our planet deserve special attention. To date, only a small part of the 11,000 discovered NEOs have been physically characterised. From ground and space-based observations one can determine some basic physical properties of these objects using visible and infrared spectroscopy. We present data for 13 objects observed with different telescopes around the world (NASA-IRTF, ESO-NTT, TNG) in the 0.4 – 2.5 um spectral range, within the NEOSURFACE survey (http://www.oa-roma.inaf.it/planet/NEOSurface.html). Objects are chosen from among the more accessible for a rendez-vous mission. All of them are characterised by a delta-V (the change in velocity needed for transferring a spacecraft from low-Earth orbit to rendez-vous with NEOs) lower than 10.5 km/s, well below the Solar System escape velocity (12.3 km/s). We taxonomically classify 9 of these objects for the first time. 11 objects belong to the S-complex taxonomy; the other 2 belong to the C-complex. We constrain the surface composition of these objects by comparing their spectra with meteorites from the RELAB database. We also compute olivine and pyroxene mineralogy for asteroids with a clear evidence of pyroxene bands. Mineralogy confirms the similarity with the already found H, L or LL ordinary chondrite analogues.

### Low delta-V near-Earth asteroids: A survey of suitable targets for space missions [Replacement]

In the last decades Near-Earth Objects (NEOs) have become very important targets to study, since they can give us clues to the formation, evolution and composition of the Solar System. In addition, they may represent either a threat to humankind, or a repository of extraterrestrial resources for suitable space-borne missions. Within this framework, the choice of next-generation mission targets and the characterisation of a potential threat to our planet deserve special attention. To date, only a small part of the 11,000 discovered NEOs have been physically characterised. From ground and space-based observations one can determine some basic physical properties of these objects using visible and infrared spectroscopy. We present data for 13 objects observed with different telescopes around the world (NASA-IRTF, ESO-NTT, TNG) in the 0.4 – 2.5 um spectral range, within the NEOSURFACE survey (http://www.oa-roma.inaf.it/planet/NEOSurface.html). Objects are chosen from among the more accessible for a rendez-vous mission. All of them are characterised by a delta-V (the change in velocity needed for transferring a spacecraft from low-Earth orbit to rendez-vous with NEOs) lower than 10.5 km/s, well below the Solar System escape velocity (12.3 km/s). We taxonomically classify 9 of these objects for the first time. 11 objects belong to the S-complex taxonomy; the other 2 belong to the C-complex. We constrain the surface composition of these objects by comparing their spectra with meteorites from the RELAB database. We also compute olivine and pyroxene mineralogy for asteroids with a clear evidence of pyroxene bands. Mineralogy confirms the similarity with the already found H, L or LL ordinary chondrite analogues.

### The Influence of Space Environment on the Evolution of Mercury

Mercury, due to its close location to the Sun, is surrounded by an environment whose conditions may be considered as "extreme" in the entire Solar System. Both solar wind and radiation are stronger with respect to other Solar System bodies, so that their interactions with the planet cause high emission of material from its surface. Moreover, the meteoritic precipitation plays a significant role in surface emission processes. This emitted material is partially lost in space. Although under the present conditions the surface particles loss rate does not seem to be able to produce significant erosion of the planetary mass and volume, the long-term effects over billions of years should be carefully considered to properly understand the evolution of the planet. In the early stages, under even more extreme conditions, some of these processes were much more effective in removing material from the planet’s surface. This study attempts to provide a rough estimation of the material loss rate as a function of time, in order to evaluate whether and how this environmental effect can be applied to understand the Hermean surface evolution. We show that the most potentially effective Sun-induced erosion process in early times is a combination of ion sputtering, photon stimulated desorption and enhanced diffusion, which could have caused the loss of a surface layer down to a depth of 20 m, as well as a relevant Na depletion.

### The origins and concentrations of water, carbon, nitrogen and noble gases on Earth

The isotopic compositions of terrestrial hydrogen and nitrogen are clearly different from those of the nebular gas from which the solar system formed, and also differ from most of cometary values. Terrestrial N and H isotopic compositions are in the range of values characterizing primitive meteorites, which suggests that water, nitrogen, and other volatile elements on Earth originated from a cosmochemical reservoir that also sourced the parent bodies of primitive meteorites. Remnants of the proto-solar nebula (PSN) are still present in the mantle, presumably signing the sequestration of PSN gas at an early stage of planetary growth. The contribution of cometary volatiles appears limited to a few percents at most of the total volatile inventory of the Earth. The isotope signatures of H, N, Ne and Ar can be explained by mixing between two end-members of solar and chondritic compositions, respectively, and do not require isotopic fractionation during hydrodynamic escape of an early atmosphere. The terrestrial inventory of 40Ar (produced by the decay of 40K throughout the Earth’s history) suggests that a significant fraction of radiogenic argon may be still trapped in the silicate Earth. By normalizing other volatile element abundances to this isotope, it is proposed that the Earth is not as volatile-poor as previously thought. Our planet may indeed contain up to ~3000 ppm water (preferred range : 1000-3000 ppm), and up to ~500 ppm C, both largely sequestrated in the solid Earth. This volatile content is equivalent to a ~2 (+/-1) % contribution of carbonaceous chondrite (CI-CM) material to a dry proto-Earth, which is higher than the contribution of chondritic material advocated to account for the platinum group element budget of the mantle. Such a (relatively) high contribution of volatile-rich matter is consistent with the accretion of a few wet planetesimals during Earth accretion.

### Extremely large peculiar motion of the solar system detected using redshift distribution of distant quasars

According to the cosmological principle, an observer fixed in the co-moving co-ordinate system of the expanding Universe should find the Universe to be isotropic, without any preferred directions. To such an observer the redshift distribution due to Hubble expansion of the Universe should also appear similar in all directions. However a peculiar motion of such an observer could introduce a dipole anisotropy in the observed redshift distribution; in reverse an observed dipole anisotropy in the observed redshift distribution could be used to infer the peculiar velocity of the observer with respect to the average Universe. We determine the peculiar velocity of the solar system relative to the frame of distant quasars, by studying the dipole anisotropy, if any, in the redshift distribution of a large sample of quasars distributed across the sky. The magnitude of the peculiar velocity thus determined turns out be extremely large ($9750\pm 550$ km/s; $\sim3\%$ the speed of light), and is about an order of magnitude larger than the velocity determined from the dipole anisotropy in the Cosmic Microwave Background Radiation or the value determined earlier relative to the frame of distant radio sources. Even the direction of the motion is in a direction nearly opposite to the earlier determinations. The large differences in the magnitudes of inferred motion as well as their opposite signs are rather disconcerting. A genuine difference between these velocity vectors would imply highly anisotropic Universe, with anisotropy changing with epoch. This would violate the cosmological principle where the isotropy of the Universe is assumed for all epochs, and which is the basis of modern cosmological models.

### Giant Planets

We review the interior structure and evolution of Jupiter, Saturn, Uranus and Neptune, and giant exoplanets with particular emphasis on constraining their global composition. Compared to the first edition of this review, we provide a new discussion of the atmospheric compositions of the solar system giant planets, we discuss the discovery of oscillations of Jupiter and Saturn, the significant improvements in our understanding of the behavior of material at high pressures and the consequences for interior and evolution models. We place the giant planets in our Solar System in context with the trends seen for exoplanets.

### The Debiased Kuiper Belt: Our Solar System as a Debris Disk

The dust measured in debris disks traces the position of planetesimal belts. In our Solar System, we are also able to measure the largest planetesimals directly and can extrapolate down to make an estimate of the dust. The zodiacal dust from the asteroid belt is better constrained than the only rudimentary measurements of Kuiper belt dust. Dust models will thus be based on the current orbital distribution of the larger bodies which provide the collisional source. The orbital distribution of many Kuiper belt objects is strongly affected by dynamical interactions with Neptune, and the structure cannot be understood without taking this into account. We present the debiased Kuiper belt as measured by the Canada-France Ecliptic Plane Survey (CFEPS). This model includes the absolute populations for objects with diameters >100 km, measured orbital distributions, and size distributions of the components of the Kuiper belt: the classical belt (hot, stirred, and kernel components), the scattering disk, the detached objects, and the resonant objects (1:1, 5:4, 4:3, 3:2 including Kozai subcomponent, 5:3, 7:4, 2:1, 7:3, 5:2, 3:1, and 5:1). Because a large fraction of known debris disks are consistent with dust at Kuiper belt distances from the host stars, the CFEPS Kuiper belt model provides an excellent starting point for a debris disk model, as the dynamical interactions with planets interior to the disk are well-understood and can be precisely modelled using orbital integrations.

### Variability of M giant stars based on em Kepler photometry: general characteristics

Small amounts of pre-solar grains have survived in the matrices of primitive meteorites and interplanetary dust particles. Their detailed study in the laboratory with modern analytical tools provides highly accurate and detailed information with regard to stellar nucleosynthesis and evolution, grain formation in stellar atmospheres, and Galactic Chemical Evolution. Their survival puts constraints on conditions they were exposed to in the interstellar medium and in the Early Solar System.

### In Search of Exomoons

Two decades ago, astronomers began detecting planets orbiting stars other than our Sun, so-called exoplanets. Since that time, the rate of detections and the sensitivity to ever-smaller planets has improved dramatically with several Earth-sized planets now known. As our sensitivity dives into the terrestrial regime, increasingly the community has wondered if the moons of exoplanets may also be detectable, so-called "exomoons". Their detection represents an outstanding challenge in modern astronomy and would provide deep insights into the uniqueness of our Solar System and perhaps even expand the definition of habitability. Here, I will briefly review theoretical studies exploring the formation and evolution of exomoons, which serve to guide observational searches and provide testable hypotheses. Next, I will outline the different methods which have been proposed to accomplish this challenging feat and their respective merits. Finally, initial results from observational efforts will be summarized with a view to future prospects as well.

### Screening Solutions in Modified Gravity Theories

In this work, we illustrate through a simple example the possibility of testing the chameleon screening mechanism in the Solar System using the forthcoming LISA Pathfinder mission around gravitational saddle points. We find distinctive tidal stress signatures for such models and consider the potential for constraints.

### Screening Solutions in Modified Gravity Theories [Cross-Listing]

In this work, we illustrate through a simple example the possibility of testing the chameleon screening mechanism in the Solar System using the forthcoming LISA Pathfinder mission around gravitational saddle points. We find distinctive tidal stress signatures for such models and consider the potential for constraints.

### The fast spin-rotation of a young extrasolar planet

The spin-rotation of a planet arises from the accretion of angular momentum during its formation, but the details of this process are still unclear. In the solar system, the equatorial rotation velocities and spin angular momentum of the planets show a clear trend with mass, except for Mercury and Venus which have significantly spun down since their formation due to tidal interactions. Here we report on near-infrared spectroscopic observations at R=100,000 of the young extra-solar gas giant beta Pictoris b. The absorption signal from carbon monoxide in the planet’s thermal spectrum is found to be blueshifted with respect to the velocity of the parent star by (-15+-1.7) km/sec, consistent with a circular orbit. The combined line profile exhibits a rotational broadening of 25+-3 km/sec, meaning that Beta Pictoris b spins significantly faster than any planet in the solar system, in line with the extrapolation of the known trend in spin velocity with planet mass.

### Data Analysis Methods for Testing Alternative Theories of Gravity with LISA Pathfinder

In this paper we present a data analysis approach applicable to the potential saddle-point fly-by mission extension of LISA Pathfinder (LPF). At the peak of its sensitivity, LPF will sample the gravitational field in our Solar System with a precision of several $\text{fm/s}^2/\sqrt{\text{Hz}}$ at frequencies around $1\,\text{mHz}$. Such an accurate accelerometer will allow us to test alternative theories of gravity that predict deviations from Newtonian dynamics in the non-relativistic limit. As an example, we consider the case of the Tensor-Vector-Scalar theory of gravity and calculate, within the non-relativistic limit of this theory, the signals that anomalous tidal stresses generate in LPF. We study the parameter space of these signals and divide it into two subgroups, one related to the mission parameters and the other to the theory parameters that are determined by the gravity model. We investigate how the mission parameters affect the signal detectability concluding that these parameters can be determined with the sufficient precision from the navigation of the spacecraft and fixed during our analysis. Further, we apply Bayesian parameter estimation and determine the accuracy to which the gravity theory parameters may be inferred. We evaluate the portion of parameter space that may be eliminated in case of no signal detection and estimate the detectability of signals as a function of parameter space location. We also perform a first investigation of non-Gaussian "noise-glitches" that may occur in the data. The analysis we develop is universal and may be applied to anomalous tidal stress induced signals predicted by any theory of gravity.

### A Review of Solar Type III Radio Bursts

Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.

### Triggered Star Formation and Its Consequences

Star formation can be triggered by compression from wind or supernova driven shock waves that sweep over molecular clouds. Because these shocks will likely contain processed elements, triggered star formation has been proposed as an explanation for short lived radioactive isotopes (SLRI) in the Solar System. Previous studies have tracked the triggering event to the earliest phases of collapse and have focused on the shock properties required for both successful star formation and mixing of SLRI’s. In this paper, we use Adaptive Mesh Refinement (AMR) simulation methods, including sink particles, to simulate the full collapse and subsequent evolution of a stable Bonnor-Ebert sphere subjected to a shock and post-shock wind. We track the flow of the cloud material after a star (a sink particle) has formed. For non-rotating clouds we find robust triggered collapse and little bound circumstellar material remaining around the post-shock collapsed core. When we add initial cloud rotation we observe the formation of disks around the collapsed core which then interact with the post-shock flow. Our results indicate that these circumstellar disks are massive enough to form planets and are long-lived, in spite of the ablation driven by post-shock flow ram pressure. As a function of the initial conditions, we also track the time evolution of the accretion rates and particle mixing between between the ambient wind and cloud material. The latter is maximized for cases of highest mach number.

### Electric solar wind sail applications overview

We analyse the potential of the electric solar wind sail for solar system space missions. Applications studied include fly-by missions to terrestrial planets (Venus, Mars and Phobos, Mercury) and asteroids, missions based on non-Keplerian orbits (orbits that can be maintained only by applying continuous propulsive force), one-way boosting to outer solar system, off-Lagrange point space weather forecasting and low-cost impactor probes for added science value to other missions. We also discuss the generic idea of data clippers (returning large volumes of high resolution scientific data from distant targets packed in memory chips) and possible exploitation of asteroid resources. Possible orbits were estimated by orbit calculations assuming circular and coplanar orbits for planets. Some particular challenge areas requiring further research work and related to some more ambitious mission scenarios are also identified and discussed.

### Scientific rationale of Saturn's in situ exploration

Remote sensing observations meet some limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. A remarkable example of the superiority of in situ probe measurements is illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases abundances and the precise measurement of the helium mixing ratio have only been made available through in situ measurements by the Galileo probe. This paper describes the main scientific goals to be addressed by the future in situ exploration of Saturn placing the Galileo probe exploration of Jupiter in a broader context and before the future probe exploration of the more remote ice giants. In situ exploration of Saturn’s atmosphere addresses two broad themes that are discussed throughout this paper: first, the formation history of our solar system and second, the processes at play in planetary atmospheres. In this context, we detail the reasons why measurements of Saturn’s bulk elemental and isotopic composition would place important constraints on the volatile reservoirs in the protosolar nebula. We also show that the in situ measurement of CO (or any other disequilibrium species that is depleted by reaction with water) in Saturn’s upper troposphere would constrain its bulk O/H ratio. We highlight the key measurements required to distinguish competing theories to shed light on giant planet formation as a common process in planetary systems with potential applications to most extrasolar systems. In situ measurements of Saturn’s stratospheric and tropospheric dynamics, chemistry and cloud-forming processes will provide access to phenomena unreachable to remote sensing studies. Different mission architectures are envisaged, which would benefit from strong international collaborations.

### Companions of Stars: From Other Stars to Brown Dwarfs to Planets: The Discovery of the First Methane Brown Dwarf

The discovery of the first methane brown dwarf provides a framework for describing the important advances in both fundamental physics and astrophysics that are due to the study of companions of stars. I present a few highlights of the history of this subject along with details of the discovery of the brown dwarf Gliese 229B. The nature of companions of stars is discussed with an attempt to avoid biases induced by anthropocentric nomenclature. With the newer types of remote reconnaissance of nearby stars and their systems of companions, an exciting and perhaps even more profound set of contributions to science is within reach in the near future. This includes an exploration of the diversity of planets in the universe and perhaps soon the first solid evidence for biological activity outside our Solar System.

### The Orbit of Transneptunian Binary Manw\"e and Thorondor and their Upcoming Mutual Events

A new Hubble Space Telescope observation of the 7:4 resonant transneptunian binary system (385446) Manw\"e has shown that, of two previously reported solutions for the orbit of its satellite Thorondor, the prograde one is correct. The orbit has a period of 110.18 $\pm$ 0.02 days, semimajor axis of 6670 $\pm$ 40 km, and an eccentricity of 0.563 $\pm$ 0.007. It will be viewable edge-on from the inner solar system during 2015-2017, presenting opportunities to observe mutual occultation and eclipse events. However, the number of observable events will be small, owing to the long orbital period and expected small sizes of the bodies relative to their separation. This paper presents predictions for events observable from Earth-based telescopes and discusses the associated uncertainties and challenges.

### Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars

Small planets, 1-4x the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1-2 R_e planets with orbital periods under 100 days, and 11% have 1-2 R_e planets that receive 1-4x the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 AU, and probably beyond. Mass measurements for 33 transiting planets of 1-4 R_e show that the smallest of them, R < 1.5 R_e, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: rho = 2.32 + 3.19 R/R_e [g/cc]. Larger planets, in the radius range 1.5-4.0 R_e, have densities that decline with increasing radius, revealing increasing amounts of low-density material in an envelope surrounding a rocky core, befitting the appellation "mini-Neptunes." Planets of ~1.5 R_e have the highest densities, averaging near 10 g/cc. The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. One explanation is that the fast formation of rocky cores in protoplanetary disks enriched in heavy elements permits the gravitational accumulation of gas before it vanishes, forming giant planets. But models of the formation of 1-4 R_e planets remain uncertain. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins.

### The Solar System and the Exoplanet Orbital Eccentricity - Multiplicity Relation

The known population of exoplanets exhibits a much wider range of orbital eccentricities than Solar System planets and has a much higher average eccentricity. These facts have been widely interpreted to indicate that the Solar System is an atypical member of the overall population of planetary systems. We report here on a strong anti-correlation of orbital eccentricity with multiplicity (number of planets in the system) among catalogued RV systems. The mean, median and rough distribution of eccentricities of Solar System planets fits an extrapolation of this anti-correlation to the eight planet case rather precisely. Thus, the Solar System is not anomalous among known exoplanetary systems with respect to eccentricities when its multiplicity is taken into account. Specifically, as the multiplicity of a system increases the eccentricity decreases roughly as a power law of index -1.20. A simple and plausible but ad hoc model of this relationship implies that approximately 80% of the one planet and 25% of the two planet systems in our sample have additional, as yet undiscovered, members. If low eccentricities favor high multiplicities, habitability may be more common in systems with a larger number of planets.

### The Solar System and the Exoplanet Orbital Eccentricity - Multiplicity Relation [Replacement]

The known population of exoplanets exhibits a much wider range of orbital eccentricities than Solar System planets and has a much higher average eccentricity. These facts have been widely interpreted to indicate that the Solar System is an atypical member of the overall population of planetary systems. We report here on a strong anti-correlation of orbital eccentricity with multiplicity (number of planets in the system) among catalogued RV systems. The mean, median and rough distribution of eccentricities of Solar System planets fits an extrapolation of this anti-correlation to the eight planet case rather precisely. Thus, the Solar System is not anomalous among known exoplanetary systems with respect to eccentricities when its multiplicity is taken into account. Specifically, as the multiplicity of a system increases the eccentricity decreases roughly as a power law of index -1.20. A simple and plausible but ad hoc model of this relationship implies that approximately 80% of the one planet and 25% of the two planet systems in our sample have additional, as yet undiscovered, members. If low eccentricities favor high multiplicities, habitability may be more common in systems with a larger number of planets.

### Hyperbolic meteors: interstellar or generated locally via the gravitational slingshot effect?

The arrival of solid particles from outside our solar system would present us with an invaluable source of scientific information. Attempts to detect such interstellar particles among the meteors observed in Earth’s atmosphere have almost exclusively assumed that those particles moving above the Solar System’s escape speed — particles on orbits hyperbolic with respect to the Sun– were precisely the extrasolar particles being searched for. Here we show that hyperbolic particles can be generated entirely within the Solar System by gravitational scattering of interplanetary dust and meteoroids by the planets. These particles have necessarily short lifetimes as they quickly escape our star system; nonetheless some may arrive at Earth at speeds comparable to those expected of interstellar meteoroids. Some of these are associated with the encounter of planets with the debris streams of individual comets; however, such encounters are relatively rare. The rates of occurrence of hyperbolically-scattered sporadic meteors are also quite low. Only one of every 10,000 optical meteors observed at Earth is expected to be such a locally generated hyperbolic and its heliocentric velocity is typically only a hundred meters per second above the heliocentric escape velocity at Earth’s orbit. Mercury and Venus are predicted to generate weak ‘hyperbolic meteor showers’: the restrictive geometry of scattering to our planet means that a radiant near the Sun from which hyperbolic meteors arrive at Earth should recur with the planet’s synodic period. However, though planetary scattering can produce meteoroids with speeds comparable to interstellar meteors and at fluxes near current upper limits for such events, the majority of this locally-generated component of hyperbolic meteoroids is just above the heliocentric escape velocity and should be easily distinguishable from true interstellar meteoroids.

### Weyl conformastatic perihelion advance of small body objects

In this paper we examine a static thin disk gravitational field symmetry over probe particles in the solar system. Using the Weyl conformastatic solution as thin disk model, we find a non-standard expression to perihelion advance due to the constraints imposed by the topology of the local gravitational field. We apply the model to a near-earth object 1566 Icarus asteroid and to the four main asteroids in the main belt (Ceres, Pallas, Juno and Vesta). As a result, we find a close agreement with observations.

### Tests of Modified Gravity Theories in the Solar System [Cross-Listing]

We review the case for testing preferred acceleration scale theories of gravity (sometimes falling under the guise of MOdified Newtonian Dynamics) in the Solar System using the forthcoming LISA Pathfinder (LPF) mission. Using a combination of analytical and numerical results, we suggest that different types of theory should be detectable using the predicted anomalous tidal stresses effects around the saddle points of the Newtonian gravitational field. The saddle point bubbles expected extent of $\sim 400$ km are to be contrasted with potential miss parameters of $\leq 10$ km, making such a test in easy reach of LPF. We also consider routes to constraining our theories from data, based on scenarios of both null and positive results.

### Tests of Modified Gravity Theories in the Solar System

We review the case for testing preferred acceleration scale theories of gravity (sometimes falling under the guise of MOdified Newtonian Dynamics) in the Solar System using the forthcoming LISA Pathfinder (LPF) mission. Using a combination of analytical and numerical results, we suggest that different types of theory should be detectable using the predicted anomalous tidal stresses effects around the saddle points of the Newtonian gravitational field. The saddle point bubbles expected extent of $\sim 400$ km are to be contrasted with potential miss parameters of $\leq 10$ km, making such a test in easy reach of LPF. We also consider routes to constraining our theories from data, based on scenarios of both null and positive results.

### Planet X revamped after the discovery of the Sedna-like object 2012 VP$_{113}$?

The recent discovery of the Sedna-like dwarf planet 2012 VP$_{\rm 113}$ by Trujillo and Sheppard has revamped the old-fashioned hypothesis that a still unseen trans-Plutonian object of planetary size, variously dubbed over the years as Planet X, Tyche, Thelisto, may lurk in the distant peripheries of the Solar System. This time, the presence of a super-Earth with mass $m_{\rm X} = 2-15m_{\oplus}$ at a distance $d_{\rm X}\approx 200-300$ astronomical units (AU) was proposed to explain the observed clustering of the arguments of perihelion $\omega$ near $\omega \approx 0^{\circ}$ but not $\omega\approx 180^{\circ}$ for Sedna, 2012 VP$_{\rm 113}$ and other minor bodies of the Solar System with perihelion distances $q>30$ AU and semimajor axes $a>150$ AU. Actually, such a scenario is strongly disfavored by the latest constraints $\Delta\dot\varpi$ on the anomalous perihelion precessions of some Solar System’s planets obtained with the INPOP and EPM ephemerides. Indeed, they yield $d_{\rm X}\gtrsim 496-570$ AU ($m_{\rm X}=2m_{\oplus}$), and $d_{\rm X}\gtrsim 970-1111$ AU ($m_{\rm X} = 15 m_{\oplus}$). Much tighter constraints could be obtained in the near future from the New Horizons mission to Pluto.

### Planet X revamped after the discovery of the Sedna-like object 2012 VP$_{113}$? [Cross-Listing]

The recent discovery of the Sedna-like dwarf planet 2012 VP$_{\rm 113}$ by Trujillo and Sheppard has revamped the old-fashioned hypothesis that a still unseen trans-Plutonian object of planetary size, variously dubbed over the years as Planet X, Tyche, Thelisto, may lurk in the distant peripheries of the Solar System. This time, the presence of a super-Earth with mass $m_{\rm X} = 2-15m_{\oplus}$ at a distance $d_{\rm X}\approx 200-300$ astronomical units (AU) was proposed to explain the observed clustering of the arguments of perihelion $\omega$ near $\omega \approx 0^{\circ}$ but not $\omega\approx 180^{\circ}$ for Sedna, 2012 VP$_{\rm 113}$ and other minor bodies of the Solar System with perihelion distances $q>30$ AU and semimajor axes $a>150$ AU. Actually, such a scenario is strongly disfavored by the latest constraints $\Delta\dot\varpi$ on the anomalous perihelion precessions of some Solar System’s planets obtained with the INPOP and EPM ephemerides. Indeed, they yield $d_{\rm X}\gtrsim 496-570$ AU ($m_{\rm X}=2m_{\oplus}$), and $d_{\rm X}\gtrsim 970-1111$ AU ($m_{\rm X} = 15 m_{\oplus}$). Much tighter constraints could be obtained in the near future from the New Horizons mission to Pluto.

### Planet X revamped after the discovery of the Sedna-like object 2012 VP$_{113}$? [Replacement]

The recent discovery of the Sedna-like dwarf planet 2012 VP$_{\rm 113}$ by Trujillo and Sheppard has revamped the old-fashioned hypothesis that a still unseen trans-Plutonian object of planetary size, variously dubbed over the years as Planet X, Tyche, Thelisto, may lurk in the distant peripheries of the Solar System. This time, the presence of a super-Earth with mass $m_{\rm X} = 2-15m_{\oplus}$ at a distance $d_{\rm X}\approx 200-300$ astronomical units (AU) was proposed to explain the observed clustering of the arguments of perihelion $\omega$ near $\omega \approx 0^{\circ}$ but not $\omega\approx 180^{\circ}$ for Sedna, 2012 VP$_{\rm 113}$ and other minor bodies of the Solar System with perihelion distances $q>30$ AU and semimajor axes $a>150$ AU. Actually, such a scenario is strongly disfavored by the latest constraints $\Delta\dot\varpi$ on the anomalous perihelion precessions of some Solar System’s planets obtained with the INPOP and EPM ephemerides. Indeed, they yield $d_{\rm X}\gtrsim 496-570$ AU ($m_{\rm X}=2m_{\oplus}$), and $d_{\rm X}\gtrsim 970-1111$ AU ($m_{\rm X} = 15 m_{\oplus}$). Much tighter constraints could be obtained in the near future from the New Horizons mission to Pluto.

### Lie-series for orbital elements -- I. The planar case

Lie-integration is one of the most efficient algorithms for numerical integration of ordinary differential equations if high precision is needed for longer terms. The method is based on the computation of the Taylor-coefficients of the solution as a set of recurrence relations. In this paper we present these recurrence formulae for orbital elements and other integrals of motion for the planar $N$-body problem. We show that if the reference frame is fixed to one of the bodies — for instance to the Sun in the case of the Solar System –, the higher order coefficients for all orbital elements and integrals of motion depend only on the mutual terms corresponding to the orbiting bodies.

### Deuterium Fractionation: the Ariadne's Thread from the Pre-collapse Phase to Meteorites and Comets today

The Solar System formed about 4.6 billion years ago from a condensation of matter inside a molecular cloud. Trying to reconstruct what happened is the goal of this chapter. For that, we put together our understanding of Galactic objects that will eventually form new suns and planetary systems, with our knowledge on comets, meteorites and small bodies of the Solar System today. Our specific tool is the molecular deuteration, namely the amount of deuterium with respect to hydrogen in molecules. This is the Ariadne’s thread that helps us to find the way out from a labyrinth of possible histories of our Solar System. The chapter reviews the observations and theories of the deuterium fractionation in pre-stellar cores, protostars, protoplanetary disks, comets, interplanetary dust particles and meteorites and links them together trying to build up a coherent picture of the history of the Solar System formation. We emphasise the interdisciplinary nature of the chapter, which gathers together researchers from different communities with the common goal of understanding the Solar System history.

### Solar System Observations with JWST

The James Webb Space Telescope will enable a wealth of new scientific investigations in the near- and mid-infrared, with sensitivity and spatial/spectral resolution greatly surpassing its predecessors. In this paper, we focus upon Solar System science facilitated by JWST, discussing the most current information available concerning JWST instrument properties and observing techniques relevant to planetary science. We also present numerous example observing scenarios for a wide variety of Solar System targets to illustrate the potential of JWST science to the Solar System community. This paper updates and supersedes the Solar System white paper published by the JWST Project in 2010 (Lunine et al., 2010). It is based both on that paper and on a workshop held at the annual meeting of the Division for Planetary Sciences in Reno, NV in 2012.

### Setting the Stage for Habitable Planets

Our understanding of the processes that are relevant to the formation and maintenance of habitable planetary systems is advancing at a rapid pace, both from observation and theory. The present review focuses on recent research that bears on this topic and includes discussions of processes occurring in astrophysical, geophysical and climatic contexts, as well as the temporal evolution of planetary habitability. Special attention is given to recent observations of exoplanets and their host stars and the theories proposed to explain the observed trends. Recent theories about the early evolution of the Solar System and how they relate to its habitability are also summarized. Unresolved issues requiring additional research are pointed out, and a framework is provided for estimating the number of habitable planets in the Universe.

### Further considerations on layer-oriented adaptive optics for solar telescopes [Replacement]

The future generation of telescopes will be equipped with multi-conjugate adaptive optics (MCAO) systems in order to obtain high angular resolution over large fields of view. MCAO comes in two flavors: star- and layer-oriented. Existing solar MCAO systems rely exclusively on the star-oriented approach. Earlier we have suggested a method to implement the layer-oriented approach, and in view of recent concerns we now explain the proposed scheme in further detail. We note that in any layer-oriented system one sensor is conjugated to the pupil and the others are conjugated to higher altitudes. For the latter not all the sensing surface is illuminated by the entire field-of-view. The successful implementation of nighttime layer-oriented systems shows that the field reduction is no crucial limitation. In the solar approach the field-reduction is directly noticeable because it causes vignetting of the Shack-Hartmann sub-aperture images. It can be accounted for by a suitable adjustment of the algorithms to calculate the local wave-front slopes. We dispel a further concern related to the optical layout of a layer-oriented solar system.

### Further considerations on layer-oriented adaptive optics for solar telescopes

The future generation of telescopes will be equipped with multi-conjugate adaptive optical (MCAO) systems in order to obtain high angular resolution within large fields of view. MCAO comes in two flavors: star- and layer-oriented. Existing solar MCAO systems rely exclusively on the star-oriented approach. Earlier we have suggested a method to implement the layer-oriented approach, and in view of recent concerns we now explain the proposed scheme in further detail. We note that in any layer-oriented system, one sensor is conjugated to the pupil and the others are conjugated to higher altitudes. For the latter the sensing surface is illuminated by only part of the field-of-view. Nighttime layer-oriented systems correct for this field reduction in terms of the pyramid sensors, which indicate the phase shift directly. Their successful implementation shows that the field reduction is no crucial limitation. In the solar approach the images recorded behind the Shack-Hartmann sub-apertures are vignetted due to the field reduction, and here this can be accounted for by a suitable adjustment of the algorithms to calculate the local wave-front slopes. A further concern we dispel relates to the optical layout of a layer-oriented solar system.

### Further considerations on layer-oriented adaptive optics for solar telescopes [Replacement]

The future generation of telescopes will be equipped with multi-conjugate adaptive optical (MCAO) systems in order to obtain high angular resolution within large fields of view. MCAO comes in two flavors: star- and layer-oriented. Existing solar MCAO systems rely exclusively on the star-oriented approach. Earlier we have suggested a method to implement the layer-oriented approach, and in view of recent concerns we now explain the proposed scheme in further detail. We note that in any layer-oriented system, one sensor is conjugated to the pupil and the others are conjugated to higher altitudes. For the latter the sensing surface is illuminated by only part of the field-of-view. Nighttime layer-oriented systems correct for this field reduction in terms of the pyramid sensors, which indicate the phase shift directly. Their successful implementation shows that the field reduction is no crucial limitation. In the solar approach the images recorded behind the Shack-Hartmann sub-apertures are vignetted due to the field reduction, and here this can be accounted for by a suitable adjustment of the algorithms to calculate the local wave-front slopes. A further concern we dispel relates to the optical layout of a layer-oriented solar system.

### The secular evolution of the Kuiper belt after a close stellar encounter [Replacement]

We show the effects of the perturbation caused by a passing by star on the Kuiper belt objects (KBOs) of our Solar System. The Kuiper belt is sampled using up to 131,072 bodies on nearly circular orbits distributed in a ring of surface density $\Sigma \sim r^{-2}$. The dynamics of the KB is followed by direct $N$- body simulations. The growth of a dynamically hot population as well as the population in resonance orbits with the planets, depends on the distribution of individual masses of Kuiper belt objects, the total mass and its radial extent, as well as on the mass and the orbit of the passing by star. The Kuiper belt is rather fragile for an encounter with a passing star, and the cross section threshold above which a recognizable structure is left are quite small. We chose for the encountering star a mass 0.5 MSun, to 2 MSun, with an impact parameter of 170 AU (for a 0.5 MSun star) to 220 AU (for 2 MSun) and an inclination angle ($\theta$) of $60^\circ$ (for 0.5 MSun) to $120^\circ$ (for 2 MSun). This results in a post encounter distribution which compares best to the currently observed population. These encounters, however, tend to excite the cold population ($e \leq 0.1$ around $a\sim 40$ AU), and consequently repletes this area. Subsequent secular evolution of the Kuiper belt can repopulate this area in less than 1 Myr if at least $\geq 35\%$ of the KBOs are relatively massive ($m \sim M_{Pluto}$). However, we did not consider the effect of the secular evolution of a larger population of somewhat less massive objects over a longer time scale, which may result in a similar repopulation of the cold Kuiper belt. We therefore speculate that the early Kuiper belt contained a rich ($\geq 35\%$) population of objects with mass $\sim M_{\rm Pluto}$.

### You need to log in to vote

The blog owner requires users to be logged in to be able to vote for this post.

Alternatively, if you do not have an account yet you can create one here.