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Workshop Programme

for period 8 - 11 November 2009

Dynamics of Outer Planetary Systems

8 - 11 November 2009

Timetable

Sunday 8 November
18:00-20:00 Welcome reception at Pollock Halls
Monday 9 November
08:30-09:20 Registration
09:20-09:30 Welcome
Session: 1 - Observations
09:30-10:20 Kalas, P (UC, Berkeley)
  Observations of outer extrasolar planets
 

Several extrasolar planets located more than ~10 AU from their host stars have been recently discovered using direct imaging techniques. I will present the latest information concerning these outer extrasolar planets, including efforts to characterize the Fomalhaut and HR 8799 planetary systems. I will also review major observing campaigns planned for the next few years that will increase this sample by at least a factor of ten.

 
10:20-10:40 Baluev, R (Pulkovo Observatory)
  Hints of the fourth planet around upsilon Andromedae
 

We analyse the array of 288 recently published new and revised Lick observatory radial velocity (RV) measurements of $\upsilon$ And. The periodogram analysis reveals three RV periodicities of relatively small semi-amplitudes (about 10 m/s), in addition to the variations due to three known Jovian planets. These new periods are about 12 years, 180 and 360 days. The two latter variations cannot be interpreted as planetary signatures because of the dynamical stability argument. These annual variations have to be interpreted as errors in the RV data, which may have instrumental or data reduction nature. The long-period RV variation may allow stable orbital configurations and is consistent with the fourth distant planetary companion. Its orbital period is unconstrained from the upper side (longer periods require higher eccentricities, up to a parabolic orbit), but its minimum mass $m\sin i$ is likely between 0.5 and 3.0 times Jupiter mass. The condition of the dynamical stability limits the set of possible orbits of the fourth planet to the 3/1, 4/1, 5/1, 6/1 mean-motion resonances with planet d or to longer-period elongated orbits with pericenter distance of 5-6 AU (with semi-major axis larger than ~10 AU). We also discuss non-planetary interpretations for the long-term RV variation, which are currently difficult to rule out. Efficient confirmation and verification of this planet candidate can be done by means of, e.g., long-term astrometry and star magnetic activity monitoring.

 
10:40-11:00 Poster presentations 1
11:30-12:20 Greaves, J (St Andrews)
  Debris disk imaging and evolution
 

I will discuss imaging of debris discs over the last twenty years, in particular in the optical (scattered light) and submillimetre (thermal emission). Resolved images contain much information about the distribution of dust and so the locations of the parent comet belts and any perturbing planets. Some surprising results have emerged recently on the ensemble of dusty discs of nearby stars, that help to place the Solar System in context. I will discuss the time history of debris, in particular whether mature systems (Gyr ages) can remain very dusty.

 
12:20-12:40 Chen, C (STScI)
  Debris disks in the nearest OB association
 

We have obtained Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) 24 micron and 70 micron photometry and high spectral resolution Magellan MIKE visual spectra (3500-9500 A; R~50,000) of 113 nearby (within 150 pc from the sun), Hipparcos F- and G-type common proper motion members of the nearest OB association, Scorpius-Centaurus. We measure 24 micron disk fractions of 6/18 (33% +/- 14%), 19/49 (39% +/- 9%), and 8/46 (17% +/- 6%) for Upper Scorpius (~5 Myr), Lower Centaurus Crux (~16 Myr), and Upper Centaurus Lupus (~17 Myr), respectively. The magnitude of these excesses (up to 200 times the predicted photospheric flux) is comparable to that expected to be generated by parent bodies at distances similar to the Jovian planets during the epoch of terrestrial planet formation, consistent with the models of Kenyon & Bromley. Since young solar-like stars are expected to possess strong stellar winds, we searched for an anti-correlation between disk fractional infrared luminosity, LIR/L*, and (1) stellar fractional x-ray luminosity, LX/L*, (2) stellar rotational velocity, v sin i, and (3) the calcium activity index, R'HK, to determine whether stellar wind drag is an important grain removal mechanism. We find evidence suggesting that stellar wind drag may play an important role in grain dynamics around 5-20 Myr old solar-like stars.

 
12:40-13:00 Churcher, L (Cambridge)
  Resolved debris disks around young main sequence stars eta Tel and HR4796A: tracing planets in the dust
 

Circumstellar dust exists in disks around hundreds of main sequence stars. These stars show significant excess emission in the mid-infrared, several million years after the proto-planetary disk is thought to have dispersed. As the lifetime of small dust around these stars is short it must be continually replenished through collisions between larger planetesimal, analogous to the bodies in the Solar System's Asteroid and Kuiper belts. These dust disks are known as debris disks. Here we present resolved mid-infrared imaging with Gemini instruments TReCS and MICHELLE of the debris disks of two young main sequence stars: Eta Tel (A0V ~10Myr) and HR4796A (A0V ~12Myr) and consider the implications for the state of planet formation in these systems. Modelling of the Eta Tel system indicates that the extension arises from an edge-on disk of radius ~24AU, but that >50% of the 18um emission comes from an unresolved dust component at ~4AU, a radial structure reminiscent of the asteroid and Kuiper belts in the Solar System. However, both the radius and dust level of the extended cooler component is also consistent with self-stirring models in which case the hot dust component may arise in massive collisions due to ongoing terrestrial planet formation.

 
11:00-11:30 Coffee & Tea
13:00-14:00 Lunch and Posters
Session: 2 - Solar System
14:00-14:50 Morbidelli, A (Observatoire de Nice)
  Outer Solar System formation and evolution
 

I will discuss how the giant planets of our solar system could avoid Type II migration towards the Sun. The dynamics, ruled by the interaction of Jupiter and Saturn with the gas disk would have left the four giant planets on fully resonant orbits with very small eccentricities and inclinations. After the disappearance of the gas disk, the interaction of the planets with the planetesimals extracted the former from their original quadruple resonance and led to a late but short phase of dynamical instability in the planetary motion. The current orbital configuration of the giant planets could then be achieved from the gravitational interaction between the planets and the disk of planetesimals. In particular, we will discuss how the amplitudes of the secular modes that characterize the current secular motion of the planets could be achieved. In the scenario where the dynamical instability of the giant planets occurred late, which is tempting to explain the origin of the so-called Late Heavy Bombardment, the orbital stability of the terrestrial planets is at risk. I will discuss how the terrestrial planets could have survived the sweeping of powerful secular resonances through their region and eventually acquire their current orbits. Constraints from the orbital distribution in the asteroid belt will also be discussed, as well as the origin of the orbital architecture of the Kuiper belt and of the systems of irregualr satellites.

 
14:50-15:10 Emel'yanenko, V (RAS)
  Evidence of outer planet migration in the orbital distribution of the Kuiper belt objects
 

The Kuiper belt consists of two main groups which are usually called the 'hot' and 'cold' populations. Very different orbital and physical properties of these populations imply a different dynamical origin. While the 'hot' population could be delivered to the Kuiper belt from the region interior to ~35 AU during the high-eccentricity phase of Neptune's migration (Levison et al., 2008, Icarus, 196, 258), the explanation of the origin for the 'cold' population needs considering processes with much smaller dynamical excitation. We investigate dynamical features of migration of low mass planets into the Kuiper belt region. Various profiles for the surface density of a planetesimal disk and masses of migrating planets are studied. It is shown that an Earth-mass planet, typically, reverses its migration near an outer edge of the planetesimal disc. Many objects move from the inner planetesimal disc to the Kuiper belt region during the planetary migration. After transferring objects to the Kuiper belt the planet returns to the inner region. The migration of the Earth-mass planet in the trans-Neptunian planetesimal disk reproduces well general orbital characteristics of the 'cold' Kuiper belt population.

 
15:10-15:30 Pan, M (Princeton)
  Secular chaos in the solar system
 

Motivated by Laskar's 2008 finding that secular interactions among the eight major solar system planets 1) cause the four inner planets to act chaotically and 2) induce much larger eccentricity/inclination variations for Mercury than for Venus, Earth, or Mars, we investigate higher-order couplings between the normal modes of the classical Laplace-Lagrange secular theory. We do this by constructing, in effect, a secular theory for these normal modes; we include long-term effects of near two-body mean-motion resonances among the outer planets. We study the effects on both the giant planets and on test particles (e.g. asteroids/Kuiper belt objects) of the resulting weak nonlinear couplings between the normal modes dominating inner- and outer-planet motions.

 
16:00-16:50 Chiang, E (UC, Berkeley)
  Planet Formation in the Outer Limits: Collisional or Collisionless?
 

It has been suggested (Goldreich et al. 2004, Annual Reviews) that planets like Neptune can form in situ at large stellocentric distances by accreting rapidly from massive disks of small, highly collisional, possibly sub-meter-sized bodies. The small bodies have their velocity dispersions damped by inelastic collisions and/or gas drag, and are accreted by protoplanets in strongly gravitationally focused collisions. Left unsolved is the problem of "cleaning up" the excess disk mass not consumed by planets. We review the status of this proposal, and ask whether observations of extrasolar debris disks such as AU Mic and Fomalhaut support it. We touch on two classic problems related to clean-up: whether resonant Kuiper belt objects incontrovertibly imply capture by a smoothly migrating Neptune, and the role of collisions in delivering Jupiter-family comets from the Kuiper belt.

 
16:50-17:10 Booth, M (Cambridge)
  How common are extrasolar late heavy bombardments?
 

Recent infra-red surveys of FGK stars have shown that 4% of stars exhibit 24 µm excess and 16% exhibit 70 µm excess indicating the presence of debris discs. In many cases these discs occur 10s or even 100s of AU from the central star, analogous to our own Kuiper belt. Studies of the history of our own Solar System show that the primordial Kuiper belt was once much more massive than it is now. Interactions between the Kuiper belt and the outer planets caused the outer planets to migrate. The Nice model shows that this migration could have been the cause of the Late Heavy Bombardment (LHB) on the Moon, which occurred 3.8 Gya. Here we investigate whether LHB-like events may have occured in extrasolar systems. We develop a model of how the Solar System would have appeared to a distant observer during its history based on the Nice model. We show that the Solar System would have been amongst the brightest of systems with debris discs before the LHB at both 24 and 70 µm. We find a significant increase in 24 µm emission during the LHB, which rapidly drops off and becomes undetectable within 30 Myr, whereas the 70 µm emission remains detectable until 360 Myr after the LHB. Comparison with the statistics of debris disc evolution shows that such heavy bombardment events must be rare occurring around less than 12% of Sun-like stars and with this level of incidence we would expect approximately one of the 413 Sun-like, field stars so far detected to have a 24 µm excess to be currently going through an LHB.

 
17:10-17:40 Discussion
15:30-16:00 Coffee and Tea
Tuesday 10 November
Session: 3 - Planetesimal growth
09:30-10:20 Alexander, R (Leiden)
  Outer disc evolution
 

I review the processes that govern protoplanetary disc evolution, focusing in particular on the outer regions of discs (beyond a few tens of AU). I will highlight the mechanisms by which gas is removed from the outer disc, and discuss a number of new theoretical results in this field. I will also consider the link to observations, and discuss how observations of both discs and planets can inform our understanding of how protoplanetary discs evolve.

 
10:20-10:40 Tilling, I (Edinburgh)
  Radiation thermo-chemical models of protoplanetary disks
 

The gas in protoplanetary disks plays host to any number of microphysical and chemical processes. By solving the chemical network coupled to 2D radiative transfer and hydrostatic balance calculations, self-consistent steady state models can be obtained for the thermal and chemical disk structure. These models can be used as input for atomic and molecular line transfer calculations in order to predict the line emission characteristics and SED continuum for a given model. This represents a powerful tool for probing the vertical and radial structure of protoplanetary disks. I present work done with the thermo-chemical disk model ProDiMo, and outline the potential of current missions such as Herschel to constrain these models. The line emission is sensitive in general to conditions in the cool outer disk (at several hundred AU from the central object), and so can be used to probe these regions and constrain the initial conditions for planet formation.

 
10:40-11:00 Poster presentations 2
11:30-12:20
  tba
12:20-12:40 Zhou, J-L (Nanjing)
  N-body simulation of later star planetary formation: comparing to observations
 

The detected explanted systems show orbital characteristic quite different to our solar systems. While planets in solar systems are in near-circular orbits and have a moderate distance to the sun, lots of exoplanets locate either in close-in orbits, or in eccentric orbits. To understanding the underlying factors, we performed N-body simulation on the late stage planet formation. Some major signatures of the observed eoxplanets are reproduced, especially the eccentricity-semimajor relation. We also find that the depletion timescale of protoplanetary disk makes the difference between the solar system and exoplanet systems. A planetary category is proposed according to this effect.

 
12:40-13:00 Haghighipour, N (Hawaii)
  Planetesimal Capture as a Clue to the Formation of Gas-Giants
 

Prior to the last stage of the formation of a giant planet, the core of this object is surrounded by an extended gaseous envelope. The models of giant planet formation suggest that, to the first order, this envelope should have a strictly solar composition. However, measurements by Galileo spacecraft have indicated a higher-than-solar abundance of heavy elements in the atmosphere of Jupiter. During giant planet formation, the Solar System is populated by km-sized and larger bodies, many of which may scatter into the giant planet's proto-atmosphere where their dynamics is affected by gas drag. As a result, these objects may be captured entirely, or may deposit some of their materials in passing through the envelope. We have studied the interactions of planetesimals with the gaseous envelope of an evolving giant planet, and have computed the efficiency of their capture and of the deposition of different elements. We present the results of our study and discuss the relation between the physical and dynamical properties of planetesimals, and the rate of their mass deposition. Since a planet formed by the disk instability scenario will have very different capture cross-sections over time than a planet formed by the core accretion model, our study should help to differentiate between these two scenarios, as well.

 
11:00-11:30 Coffee and Tea
13:00-14:00 Lunch and Posters
Session: 4 - Planetesimal evolution
14:00-14:50 Tremaine, S (Princeton)
  Long-lived N-body disks
 

Many of the same physical processes drive the evolution of circumstellar discs composed of dust grains, asteroids, planetesimals, planets, etc. This talk investigates the survival of such discs over Gyr timescales, using a unified approach that is applicable to all Keplerian discs of solid bodies. Monodisperse discs can be characterized locally by four parameters: surface density, semi-major axis, velocity dispersion, and size of the bodies. For a given set of these parameters, the disc must survive all dynamical processes, including gravitational instability, dynamical chaos, gravitational scattering, physical collisions, and radiation forces, that would lead to significant evolution over its lifetime. These processes lead to a rich set of constraints that strongly restrict the possible properties of long-lived discs. Within this framework, I also discuss the detection of planetesimal discs using radial velocity measurements, transits, microlensing, and the infrared emission from the planetesimals themselves or from dust generated by planetesimal collisions. A wide range of long-lived discs would not have been detected by present techniques.

 
14:50-15:10 Parker, R (Sheffield)
  The role of cluster evolution in disrupting outer planetary systems via the Kozai mechanism
 

Several studies have shown that a high proportion of exoplanets orbit a component of a binary system. It is thought that the Kozai mechanism may play a significant role in disrupting the orbits of planets in binary systems, and it has been shown that it can cause high eccentricities in planetary orbits. I show that the Kozai mechanism can be induced in planets orbiting binary components by the dynamical processing of the initial population in a typical star cluster. In particular, I discuss the implications of the Kozai mechanism for outer planetary systems.

 
15:10-15:30 Davies, M (Lund)
  Effects of crowdedness on planetary systems containing planets on wide orbits
 

We consider the effects of high stellar number densities on planetary systems containing planets on relatively wide orbits. In crowded places such as young stellar clusters, a large fraction of stars will experience close encounters with passing stars, or exchange into binaries. Fly-bys can induce instabilities within planetary systems, whilst companion stars can change the eccentricity of planetary orbits via the Kozai mechanism. Planets on wider orbits will generally be more vulnerable to such effects. Here we consider the survival chances of wide planetary systems as a function of stellar cluster properties (mass and radius of cluster).

 
16:00-16:50 Krivov, A (Friedrich-Schiller-Universität Jena)
  Collisional evolution of debris disks: Unraveling planetesimals and planets
 

Debris disks around main-sequence stars are believed to derive from planetesimal populations that have accreted at early epochs and survived possible planet formation processes. Being stirred by the largest embedded bodies and/or giant planets, these planetesimals undergo a collisional cascade that grinds them to smaller objects of all sizes down to tiny dust, until the latter is removed by direct radiation pressure, drag forces, and various erosive processes. I will briefly review essential physics of debris disks and modeling methods. I will then concentrate on the central question of debris disk studies: how do observations of debris dust, interpreted through collisional and dynamical models, constrain the invisible planetesimals, known or alleged planets in the systems, and the history of planetesimals and planets? Specifically, what can we learn about the current mass, location, extension, and dynamical excitation of planetesimals, optical and mechanical properties of solids, and the collisional processes that grind them to dust? To what extent can we infer the initial size distribution of the planetesimal belt at the onset of the collisional cascade and find out what and when may have ignited it? These questions will be addressed from the perspective of (i) the observed statistics of a large number of unresolved debris disks, (ii) SEDs of individual unresolved systems, and (iii) detailed datasets on selected resolved disks.

 
16:50-17:10 Debes, J (NASA Goddard Space Flight Center)
  Interstellar medium sculpting of nearby debris disks
 

Many nearby debris disks that have been resolved in scattered light show a variety of twists, warps, or asymmetries. Often these features are noted and the presence of unseen planetary companions is inferred. However, the outer regions of debris disks can be impacted by the surrounding interstellar environment. In this talk, I present a simple model involving supersonic gas drag on debris disk dust particles that explains the scattered light observations of HD 61005, HD 15115, and HD 32297, three perturbed debris disks.

 
17:10-17:40 Discussion
15:30-16:00 Coffee and Tea
19:30-22:00 Wine reception and conference dinner at Pentland West
Wednesday 11 November
Session: 5 - Origin of outer planets
09:30-10:20 Rice, K (Edinburgh)
  In-situ formation by gravitational instability
 

It is quite likely that during the earliest stages of star formation, protostellar disc will be massive relative to the mass of the central star and that their evolution will be driven primarily by self-gravity. If such discs become extremely gravitationally unstable, they may fragment to form bound objects that could contract to form giant planets or sub-stellar objects. It is now generally accepted, however, that such a process cannot operate effectively in the inner parts of these discs, but that it may operate at large radii (r > 50 AU). We consider here the conditions required for discs to undergo fragmentation and discuss when this should happen, what types of objects might form, and if there is any current observational evidence to support such a process.

 
10:20-10:40 Meru, F (Exeter)
  Exploring the conditions required to form planets in realistically modelled self-gravitating discs
 

We present new results on giant planet formation by fragmentation of large self-gravitating discs. The early evolution of such massive discs has been considered using cooling parameters to describe the thermodynamics (e.g. Lodato & Rice 2004) and using grid-based (e.g. Cai et al. 2008; Boss 2004) and hydrodynamical (e.g. Stamatellos & Whitworth 2008) radiative transfer calculations. We present new results from simulations using a Smoothed Particle Hydrodynamics code with flux-limited diffusion to follow disc evolutions in order to simulate more realistically the physical processes of energy transfer that may occur in such massive and extended discs, as well as the effects of stellar irradiation and differing disc opacities. We discuss the possibility of fragmentation at radii of O(100) AU, particularly focussing on the cooling rates in such discs by comparing them with the fragmentation criterion of Gammie (2001) and Rice et al (2005). Moreover, we also discuss the applicability of these criterion as well as those of Rafikov (2005) and Clarke (2009) in such discs. Furthermore, we consider the likelihood of fragmentation if the disc photosphere is cooled (which may occur if for example, shadowing were to take place).

 
10:40-11:00 Forgan, D (Edinburgh)
  Direct synthetic imaging of smoothed particle hydrodynamics density fields, and implications for observations of outer planetary systems
 

With the next generation of ground and space-based telescopes (e.g. Herschel, ALMA, e-Merlin) bringing improved resolution to bear on emergent planetary systems, theory and simulation must keep pace to interpret observations. We present a means of directly incorporating Monte Carlo Radiative Transfer (MCRT) techniques into Smoothed Particle Hydrodynamics (SPH) density fields. This allows us to produce synthetic telescope images of these simulations, and to determine the visibility of nonaxisymmetric features such as spiral arms and disc clumps. We demonstrate the technique by considering the HL Tau system, found by Greaves et al (2008) to have a condensation of mass 15 Jupiter masses at ~65 AU (for which they produced an SPH simulation with similar features). We image the SPH simulation to determine the visibility of this clump by the next generation of sub-mm instruments.

 
11:30-12:20 Kley, W (Tübingen)
  Outward migration from inner regions
 

Observations tell us that planets should have migrated from the location where they formed to their present position. This migration process is typically invoked to explain the 'hot' planets close to the parent star, as it was believed that migration typically occurs inward. Recent studies have opened the possibility of outward migration depending either on the thermodynamical properties of the disk, or on rapid type III migration. In this contribution I will discuss the possiblity of sustained outward planetary migration in disks in order to explain the observed planets at distances of about 100au.

 
12:20-12:40 Veras, D (Florida)
  Formation, survival, and detectability of planets beyond 100AU
 

Direct imaging searches have begun to detect planetary and brown dwarf companions and to place constraints on the presence of giant planets at large separations from their host star. This work helps to motivate such planet searches by predicting a population of young giant planets that could be detectable by direct imaging campaigns. Both the classical core accretion and the gravitational instability model for planet formation are hard-pressed to form long-period planets *in situ*. Here, we show that dynamical instabilities among planetary systems that originally formed multiple giant planets much closer to the host star could produce a population of giant planets at large (~100 AU -- 100000 AU) separations. We estimate the limits within which these planets may survive, quantify the efficiency of gravitational scattering into both stable and unstable wide orbits, and demonstrate that population analyses must take into account the age of the system. We predict that planet scattering creates detectable giant planets on wide orbits that decrease in number on timescales of ~10 Myr. We demonstrate that several members of such populations should be detectable with current technology, quantify the prospects for future instruments, and suggest how they could place interesting constraints on planet formation models.

 
12:40-13:00 Malmberg, D (Lund)
  Producing wide offset planets from fly-bys on initially stable planetary systems
 

Recent observations have revealed a population of planets with separations larger than 100 au from their host stars (see, for example, Kalas et al. 2008; Marois et al. 2008). These planets need not have formed at such large separations. Instead they may, for example, have been put there by planet-planet scatterings in planetary systems with planets on initially tight and unstable orbits (Scharf & Menou 2009; Veras, Crepp & Ford 2009). Here we explore an alternative to systems which form with planets on unstable orbits. We consider systems which are stable if left alone, but which become unstable by the interaction with a passing star in a fly-by. This causes strong planet-planet scatterings to occur, which in turn produce wide offset planets (Malmberg, Davies & Heggie 2009, in prep.). Thus, planetary systems which would otherwise be stable will also contribute to the population of wide offset planets.

 
11:00-11:30 Coffee and Tea
13:00-14:00 Lunch and Posters
Session: 6 - Interactions with outer planets
14:00-14:50 Ferraz-Mello, S (São Paulo)
  Phase portrait of the planetary 2:1 resonance
 

Uranus-Neptune and 6 pairs amongst the more than 400 exoplanets currently known show periods close to a 2:1 commensurability. In the most conspicuous case, Gliese 876, the two planets are very close to a stationary solution in which both orbits have aligned semi-major axis and the motion on them is such that the conjunction of the two planets occurs when the two planets are at pericenter (symmetric conjunction). This solution is referred in the literature as an “apsidal corotation resonance” (the two bodies corotate with the features of the changing mutual gravitational field). The analysis of these motions shows other possibilities which may be anti-symmetric (the pericenters lie on opposite directions) or asymmetric (the semi-axes are frozen but at angles different of 0 or ). However, ACRs are not the only possible resonant motions. In some actual cases, the planets are in resonant motion but not in a stationary configuration. The best known example is the pair of planets of HD 82943. In this case, the motion of the planets is a composition of two different proper oscillations around two families of periodic solutions which intersect at an ACR. The region where the motion occurs is surrounded by a very chaotic domain (in fact the published best fit solution lies in this chaotic domain). We intend to present the results of an exploration of the phase space around stable and unstable ACRs in two main cases: The case of HD 82943 and that of two planets with the same masses as Jupiter and Saturn. We show how the phase portrait is different following the more massive planet is the outer or the inner one in the pair, and we discuss the details of these portraits.

 
14:50-15:10 Murray-Clay, R (Harvard Smithsonian Center)
  Dynamics and planet formation at wide separations: HR8799
 

The three gas giants directly-imaged orbiting HR 8799 comprise the first multi-planet system detected at wide separations around a main sequence star. Core accretion scenarios, already strained at the outer limits of our solar system, have difficulty explaining planet formation at the larger distances of the HR 8799 planets, even around a central A star. Though most plausible for massive planets at large separations, formation by gravitational instability requires that the system's protoplanetary disk passed through a fine-tuned region of parameter space at its transition from the Class I to the Class II phase. Orbital stability requirements imply that the HR 8799 planets occupy at least one and possibly two mean motion resonances, suggesting that they migrated toward one another and may have migrated substantially from their formation locations. I will discuss how the HR 8799 system constrains the formation and migration of distant planets.

 
15:10-15:30 Cuk, M (Harvard)
  Resonances as a record of planetary migration
 

While hundreds of extrasolar planetary systems have been discovered, only a small fraction of them contain more than one known planet. An even smaller fraction of known multi-planet systems are relatively compact, containing giant planet pairs with period ratios below three or four (Saturn-to-Jupiter period ratio is about 2.5). Most multi-planet systems contain planet pairs on eccentric orbits, with orbital periods varying by orders of magnitude. This is almost certainly a consequence of planet-planet scattering, which would have erased much of information about the prior dynamical evolution of the system. Current theory of planet formation suggests that there are generally two epochs of giant planet migration: one caused by interactions with the gas disk within the first few Myr of the system's history, and a later one (possibly lasting for tens to hundreds of Myr), driven by gravitational interaction between the planets and solid planetesimals. Planets with smaller masses are expected to be affected more by interactions with planetesimals, due to the limited amount of mass available as solids (cf. Raymond and Armitage 2009). We note that very massive known compact exoplanet pairs tend to occupy resonances more often than those with masses similar to Jupiter and Saturn. Using numerical simulations, we show that the non-resonant compact pairs can be plausibly derived from an initial resonant or near-resonant configuration, much like the Nice model (Tsiganis et al. 2005) proposes for our solar system. We conclude that the gas-driven migration might be often ending with many of the planets in resonances, despite the effects of turbulence (Adams et al. 2008). It is possible that after the gas has dissipated, the scattering of sizable solid protoplanets enables resonance-breaking in less massive systems but not in more massive ones. We propose observational tests of these hypotheses.

 
16:00-16:50 Duncan, M (Queen's)
  Cometary Dynamics: Connecting the inner and outer solar system
 

Observations of cometary orbits in the inner solar system contain important clues to both the outer solar system’s current structure and its past dynamical evolution. I will briefly summarize numerical simulations which have studied the dynamical origins of observed comets and link the observed populations to the reservoirs from which they are currently leaking. I will then review simulations which are designed to study the dynamical origin of the reservoirs themselves. The talk concludes with a discussion of the currently unresolved issues, particularly those related to the origin and structure of the Oort Cloud.

 
16:50-17:10 Kuchner, M (NASA Goddard Space Flight Center)
  Collisional Grooming Models of Planets Interacting with Debris Disks
 

An extrasolar planet sculpts the debris disk around Fomalhaut as Neptune sculpts the Kuiper Belt. Probably many other debris disks contain planets that we could locate if we could better recognize their signatures in the dust that surrounds them. But the interaction between planets and debris involves both orbital resonances and collisions among grains and rocks in the disks---difficult processes to model simultaneously. I will describe new 3-D models of debris disk dynamics that incorporate both collisions and resonant trapping of dust self-consistently for the first time, allowing us to decode debris disk images and better model the distribution of small bodies in our own solar system.

 
17:10-17:40 Discussion
17:40-18:10 Workshop summary
15:30-16:00 Coffee and Tea

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