The 37^th annual meeting of the AAS Division on Dynamical Astronomy took place during the last week of June in Halifax, Nova Scotia. The meeting went very well. We had an opportunity to listen to many interesting talks, to communicate with many colleagues, and to learn several new things. Halifax is a lovely town, though we saw the Sun only briefly. The lecture room in the Sobel Science Bldg. at St. Marys is superbly equipped, contributing in no small part to the success of the meeting. USNO would do very well to have just a fraction of such quality and thought put into its shamefully substandard lecture/conference room. Last, and by no means least, we had a chance to present our own communications to the judgment of the community. Both talks were well received; people asked questions, commented, and spoke to us after the session.

Murison gave a contributed paper, "On the Precision of Artificial Satellite Orbit Determination from Observations from an Orbiting Platform". Many in the audience were as captivated as Murison is by the unconventional notion of doing precision astrometry of artificial satellites from a telescope mounted on a low-Earth-orbit satellite (such as the MAPS mission being proposed by USNO). There was general acknowledgement in discussions afterward that the magnitude of difficulty of analytical approximations of the problem is surprising. Apparently, analytical characterization of orbit determination error distributions is a heretofore unvisited problem (as also born out by Murison's searches of the astronomical literature.)

Efroimsky gave a contributed paper, "On the Theories of Bodily Tides: The Models and the Physics", in collaboration with V. Lainey (l’Observatoire de Paris). For Efroimsky, this presentation was crucial for the extra reason that the "anonymous" reviewer of a paper, on which the talk was partially based, was sitting in the audience. After the talk, the anonymous reviewer openly expressed his approval of the work.

Murison spent much of the first half of the conference (in the early morning before sessions and late at night after sessions) helping the conference hosts and DDA Officers deal with various meeting-related issues. Murison is the recently re-elected DDA Secretary, so he also took the official minutes of, gave reports to, and participated in policy and decision-making discussions at the DDA Committee and Business meetings. These meetings took place Sunday before the start of the general meeting and Monday after the conclusion of that day's scientific sessions. Murison also served as the DDA's photographer for the conference (with help from Alice Monet (Flagstaff)).

Of the numerous reports and talks presented at the meeting, many were well above the run of the mill. This made for a very (in fact unusually) profitable meeting, from a dynamical perspective.

Many of the contributed papers of colleagues led Murison to think of several new and worthwhile research projects. Here are just a few:

1. Dan Scheeres's (U. Michigan) talk on the effects of solar radiation on the rotational dynamics of asteroids raised the question in Murison's mind of what happens as the asteroid spin rate approaches zero. The dynamics is likely chaotic, especially as resonances (which were touched upon by Alan Harris in his talk on binary asteroids) are traversed.
2. Kevin Walsh (U. Maryland, also one of the Student Stipend awardees) presented results of a model of NEA binary formation via tidal disruption. This led Murison to wonder if migration of binary asteroids from the main belt (mostly via secular resonances) is different in character from the single asteroids due to the slightly different perturbations experienced by the former.
3. Wayne Hayes (Irvine) gave a talk whose main point is that it appears that whether or not the outer solar system is seen to be chaotic in numerical simulations is buried inside the current observational uncertainty. This indicates to Murison that the dynamical phase space has fine-scale structure (this should not come as a surprise to researchers in chaotic dynamics) and would be a rich research avenue.
4. Mark Showalter (SETI) talked of the outer rings and chaotic orbits within the Uranian system as observed by HST. It turns out that the small moons Cupid and Belinda are not in 1:1 resonance even though they share very nearly the same semimajor axis. Murison would like to investigate the evolutionary history of these satellites (past and future) as well as determine if high-order resonances might play an important role.
5. Matt Tiscareno (Cornell) talked of the density wave response of Saturn's rings to inner Lindblad resonances with the co-orbital satellites Janus and Epimetheus, based on Cassini observations. These two satellites are in mutual horseshoe orbits, swapping places every four years. This begs the question: How stable is this configuration to the many perturbations present in the Saturnian system? Since the mass ratio of the satellites is ~4, it might be an important factor. (In such studies the satellite masses are often assumed to be infinitesimally small.)
6. It is by now well-known that the outer solar system planets migrated significantly due to scattering of planetesimals. If Jupiter (and/or the other gas giants) had already collected contingents of Trojans, then the question arises: What happens to such objects as they pass through low-order mean-motion resonances as they are dragged along with their primaries? Murison is not sure which talk sparked this question — probably either Matija Cuk's (British Columbia) paper on putative Lunar Trojans or Paul Weigert's (Western Ontario) talk on quasi-satellites (see below).
7. Toshio Fukushima (NAOJ), a frequent visitor to USNO, talked of using the Levi-Civita coordinate transform in a particular perturbed two-body problem. Regularization of the two-body problem usually makes use in one way or another of the L-C spatial transform and the Sundman time transform. Murison was prompted by this talk to wonder if the Sundman transform can be employed in solving (both numerically and analytically) the Kepler equation. This is particularly fortuitous timing as Murison is currently working on an optimal numerical method for solving the KE as a result of his work that he presented at this conference.
8. Man Hoi Lee (Santa Barbara) discussed his recent analytical work on the orbits and masses of the newly-discovered satellites of Pluto, S/2005 P1 and S/2005 P2. It would be very interesting to explore numerically the dynamics and stability of the Pluto system as we now know it, since the mass ratio of Pluto & Charon is (and hence their perturbative influences are) so very large.

Geoff Marcy (Berkeley) in his invited talk confirmed the statement made earlier by Butler, that most of the extrasolar planets follow elongated orbits. This is one of the mysteries of the planetary astronomy. Marcy clarified that the closer to the star the less high-eccentricity orbiters. This by itself is not surprising, because at close distances the orbits may have been circularized by tidal forces. The question remains how the planets initially acquire their large eccentricities. Dimitri Veras of the U of Colorado reviewed in his talk a couple of possible mechanisms. Both mechanisms emerge in pretty crowded many-body systems. No mechanism applicable to a single planet has been suggested so far. Motivated by the afore quoted talks by Marcy and Veras, Michael Efroimsky is currently developing such a mechanism.

Jim Williams of JPL, in his Brouwer Award lecture (2.4 MB PDF), provided a comprehensive review of the Lunar ranging. Among many other things, he raised the old issue of the dependence of the Lunar attenuation quality factor Q upon the tidal frequency f. In their earlier publication dated by 2001, Williams and his team reported that Q was proportional to f taken to the power of -0.19 (the 'minus' sign acting as a red flag for solid-state physicist). At this meeting, though, Williams was already talking about -0.07, an optimistic trend in Efroimsky's view. Efroimsky hopes that in another five years their team will transcend zero and will eventually report a positive factor, so that the Lunar seismology gets happily reconciled with the condensed-matter physics, and we all take a long breath. Williams's talk was a first for the DDA: since Jim does not travel, he gave his lecture remotely via telephone. This talk and the subsequent discussion, at the Meeting and then via e-mail seems to have given start to a new collaboration. Williams and Efroimsky came to an agreement that the Lunar-Ranging Team had almost certainly misinterpreted the data on attenuation in the Moon (and, possibly, in the Earth). We are now thinking of how to amend this issue.

Another excellent invited talk was given by Steven Majewski (Virginia), on Galactic structure and tidal stream dynamics. Murison had no idea so many (twenty-something!) different streams have been observationally identified, most of them in just the past few years. Interestingly, the coherence of the streams — a result of their dynamical "coldness" — enables them to be used as surprisingly sensitive probes of the Galactic potential and hence place significant constraints on cold dark matter models and models of structural evolution. Our Galaxy's environs are shockingly violent (if a bit slow on human timescales). Majewski highlighted a serious need for high-precision proper motions attainable only from space astrometry missions such as SIM.

Paul Weigert (Western Ontario) gave in his invited talk an overview of the fascinating dynamics of the so-called quasi-satellites discovered in recent years as well as horseshoes and tadpoles. His graphical and animated illustrations were particularly effective. These kinds of orbits are of particular interest to Murison since he did his dissertation research on the restricted three-body problem, in which these orbits play a central role in the overall dynamical picture of the problem. There is still much work to be done on the stability of these orbits, especially in the solar system context.

This was pretty much our weather most of the week.



Group shot of meeting participants.



Ready for lobster slaughter! L. to R.: Alice Monet (USNO Flagstaff), Pete Shelus (U. Texas), Mike A'Hearn (U. Maryland), Bill Jefferys (U. Texas).



Marc & Michael atop a 93 year old research vessel docked at the Maritime Museum.



A billboard you're not likely to see in the U.S.



Despite the dismal weather, residents of Halifax are not without a good sense of humor



Lights across the harbor of Halifax's sister city, Dartmouth.