# 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