IMG_2366Final day of the IAU meeting  general assembly found me in talks about transit-timing variations, tidal interactions, and planets in binary star systems.

The first session focused on the impressive results from transit-timing variation (TTV) studies. Since detecting and modeling TTVs is very data-intensive, the talks explored the data science aspects of TTV analysis. Ben Montet‘s talk, for example, looked at how hard it can be to detect transits in the first place, much less measure their period variations. To estimate uncertainties on their variations, he advocated using importance sampling and generating thoroughly explored prior distributions.

The next session looked at tidal interactions and planets in binary star systems. Smadar Naoz talked about her work on Kozai oscillations and how she showed that Kozai had made some fairly specific assumptions that limited his famous dynamical analysis in important ways. Her improved analysis shows that, contrary to the original results, the Kozai mechanism can actually produce planets on retrograde orbits and so can help explain the growing number of such retrograde planets.

I also spoke in the second session about Roche lobe overflow in short-period gaseous exoplanets, and I’ve posted my presentation below.

So, all in all, a really brilliant conferences in an inspiring locale. Mahalo, Hawaii.

Tidal Decay and Disruption of Gaseous Exoplanets

IMG_2332Day 3 of the conference saw several talks on spin-orbit misalignments and mean-motion resonances in exoplanetary systems.

Among the talks on spin-orbit misalignment, Josh Winn of MIT gave an excellent review of observational and theoretical developments in the field. He argued that any model to explain the misalignments must account for (1) the fact that 75% of hot Jupiters show significant misalignment, (2) misaligned systems are found preferentially around stars hotter than 6100 K, and (3) misalignments out to 10 days orbital period. Hefty requirements that no theory for misalignment has convincingly satisfied yet.

In the resonances session, Konstantin Batygin of Caltech gave a sparkling talk on his recent work looking at the establishment of resonances in planetary systems. He showed how effective resonance capture requires fairly small orbital eccentricities, less than about 0.02. His results could help explain why so many multi-planet systems are very near but not quite in resonance.

IMG_2306A quick update on day 3 of the IAU conference.

Good talks today on recent developments in our understanding of planet formation by Christophe Mordasini. Improved models for the dynamics of grains in the accretion streams for growing gas giants have helped solved some of the mysteries associated with the planets’ formation.

Aurelian Crida gave a very informative talk on developments in planetary migration. Turns out that migration can be very complicated.

And some good talks on the dynamics of mature planetary systems. Christa Van Laerhoeven reviewed classical secular theory and discussed how the orbital architectures of some systems can be determined, even in the absence of detailed information about the planets’ orbits.


IMG_2272Day 2 of the IAU meeting was very busy, with lots of great talks and presentations. Two events, in particular, stood out to me, though.

The first was a session on Highlights from Space Missions, which had a focus on results from the Dawn and Rosetta missions.

The Dawn mission visited the asteroid Vesta and is currently in orbit around Ceres, the largest asteroid in the asteroid belt and a world in its own right. By way of highlighting the recent results, the mission PI, Prof. Chris Russell, presented breath-taking images and movies from the mission. I’ve included some below.

The first movie is of a bright mountain on the surface of the asteroid Ceres called The Pyramid.

The second movie shows Occator crater with its mysteriously bright central … thing. The Dawn mission team is speculating that the bright spot is some kind of exotic salt deposit, based on its reflectance spectrum, but they’re not really sure what it is yet.

Next up, Dr. Sierks showed highlights from the the Rosetta mission, which is visiting Comet 67P and dropped the Philae lander last year onto the comet’s surface, also with mind-blowing movies.

The first movie shows the comet’s rotation, revealing its voluptuous  shape.

The next movie shows how the comet’s rotation causes its jets to curve, as the icy vapor escapes into space.

And the final movie (poorly focused unfortunately) shows the cosmic snow erupted into interplanetary space by the comet’s jets. These particles actually represent a hazard to the spacecraft and make it difficult for its operators to orient the spacecraft since they use background stars to figure out how it’s oriented. As a result, the spacecraft was moved to a more distant, safer orbit after these images were collected.

In the evening, IAU hosted an event at which they invited the public to vote on names for 20 known exoplanet systems.  Just since last night, the number of votes has gone from zero to more than 15,000.

CMFHiw0UYAAfVF5Day 1 of International Astronomical Union’s joint meeting with the American Astronomical Society in steamy Honolulu.

I attended the morning session on Dynamical astronomy in the solar system and beyond and saw some amazing talks on developments in computing planetary and satellite ephemerides, the modern day equivalent of Laplace’s Demon. These sophisticated computer programs are able to predict planetary positions to breath-taking accuracy and are sensitive enough to require including the gravitational influence of the 30 largest Trans-Neptunian Objects.

Coffee break then a late morning session on protoplanetary disks, where I learned about recent developments in the theory of disks and saw more of the beautiful disk images produced by the ALMA array.

Then a lunch session on Inclusive Astronomy led by Prof. Meredith Hughes discussing things we, as a community, can do to welcome and help people who face unusual challenges to entering and staying in the field. For example, we were advised to use sans serif fonts in our presentations because they are easier to read for those with dyslexia.

I skipped the plenary talk to attend the poster session (which were inexplicably scheduled on top of one another). I chatted with Erika Nesvold of SMACK fame about her recent result, explaining observations of an asymmetric distribution of CO in the Beta Pictoris protoplanetary disk via enhanced collisions among dust grains in the disk.

AAS 225 — Day 3

Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From

Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From

Great finish to the meeting, and thankfully no big disasters at my special session.

Lots of excellent talks, but the talk that stood out for me was Sarah Ballard’s, in which she addressed an impressively simple but compelling question: Is there a difference between planetary systems where we’ve only found one planet and systems where we’ve found more than one?

This question is important because such a difference could point to different formation and/or evolutionary processes in these systems, and so comparison of these systems could elucidate subtle but significant aspects of planet formation.

In fact, Ballard did find the two types of planetary system are different, and that, for some reason, about half of M-dwarf stars that host planets have only one.

She also found modest but intriguing differences in the stars that host single planet: their features suggest they may be older than stars with multi-planet systems. Does that mean that single-planet stars used to have multiple planets but enough time has passed that the system became dynamically unstable, leaving behind a single planet?

AAS 225 — Day 2

Blue glacial ice. From

Blue glacial ice. From

I really enjoyed Aomawa Shields‘s dissertation talk in the “Extrasolar Planets: Host Stars and Interactions” session, in which she discussed how different stellar types could influence the climates of putative Earth-like planets.

She highlighted how the ice-albedo feedback would operate differently on planets orbiting M-dwarfs as compared to those orbiting F-stars. Since they are so cool, M-dwarfs shine primarily in infrared (IR) wavelengths, while F-stars are much hotter and emit in the visible and ultraviolet (UV). At the same time, water ice primarily absorbs IR but reflects visible light.

Therefore, around an M-dwarf, the ice on an Earth-like planet’s surface would absorb a lot of the stellar insolation, heating the planet, while around an F-star, the ice would reflect it, keeping the planet cool. As a consequence, Shields argued that M-dwarf planets have climates more stable against global ice ages than F-star planets. So although there may be other challenges to life on an M-dwarf planet, climate stability is probably not one of them.

The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By regularly looking at the spectrum of a star - and so, measure its velocity - one can see if it moves periodically due to the influence of a companion. From

The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. From

Another great day at the AAS meeting. One talk that stuck out for me was the dissertation talk from Ben Nelson (PSU). I was amazed at how much he was able to squeeze into his 15 minutes and still not lose the audience.

Among the things he covered was his new MCMC code, RUNDMC, specially suited to analyze radial velocity (RV) observations of planetary systems and thoroughly but quickly sample the sprawling parameter space associated with these systems. He applied his code to several systems to understand how robustly different planetary configurations could be detected in those systems, including whether the RV data favored additional planets in a system or other kinds of variability.

Lots of amazing presentations today, running the gamut from transmission spectroscopy of hot Neptune-like planets to the detailed and puzzling architectures of multi-planet systems. But two talks really stuck out for me.

belts-plasmapause_1 The first one, by Prof. Dan Baker at U Colorado, covered recent developments in the study of the Van Allen radiation belts (which Van Allen preferred to call “zones” — when asked by a reporter what was the function of Van Allen belts, he said they hold up Van Allen’s pants). As a member of the Radiation Belt Storm Probe mission,  Baker explained what we understand and what remains mysterious about these powerful celestial phenomena suspended above our heads, including a bizarre “glass wall” that keeps charged particles at bay.


The European Space Agency’s Rosetta spacecraft captured these photos of the Philae lander descending toward, and then bouncing off, the surface of Comet 67P/Churyumov–Gerasimenko during its historic touchdown on Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/ID —

In the afternoon, Dr. Paul Weissman gave the most recent updates on the Rosetta mission, still in orbit around Comet Churyumov-Gerasimenko (which Weissman called “comet CG”). Following up on the more-exciting-than-expected landing of the Philae spacecraft, Weissman explained that the lander struck a surprisingly hard sub-surface layer (comparable in strength to solid ice), which probably contributed to the lander’s unplanned ballistic trajectory around the comet. Lots of other interesting science, including more evidence about the origin of Earth’s water.