All posts for the month August, 2015

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.

A hot Jupiter being ingested by its host star. From

A hot Jupiter being ingested by its host star. From×576/img/47b3082d767346e8bebdb5ad99f8f33d.jpg.

In journal club today, we discussed the recent study by Matsakos and Königl that investigated the possibility that hot Jupiters can be ingested by their host stars.

The idea that stars might ingest hot Jupiters has been around since the planets were first discovered. The putative accomplice in this type of astrophysical murder is tidal interaction between the planet and host star (the same kind of interactions that cause the Moon to recede from the Earth).

Tides cause the hot Jupiters to slowly spiral into their host stars, while spinning up the host star, but the strength of the interactions drops off rapidly with distance between the planet and star. The first hot Jupiters were far enough from their stars that they are probably safe from tidal destruction.

However, astronomers have continued to find planets closer and closer to their host stars, raising again the specter of planetary tidal destruction.

These same tidal interactions also align a host star’s equator to its planet’s orbital plane. So stellar equators that start out highly inclined to their hot Jupiter’s orbit (and there are a surprisingly large number) can end up completely aligned, but, as Matsakos and Königl argue, only at the cost of the planet’s orbital angular momentum.

The upshot of this is that many of the exoplanet host stars with equators aligned to their planets’ orbital planets may have eaten a hot Jupiter early in their lives. Under some reasonable assumptions, Matsakos and Königl show that the observed distribution of inclination angles for host star equators is consistent with about half of the stars having eaten a hot Jupiter.

Fortunately, the planets in our solar system will not suffer the same fate — at least not for a few billion years. But once the Sun leaves the Main Sequence and enters stellar senescence in a few billion years, its radius will blow up, destroying Mercury and Venus. Whether the Earth is also consumed by the approaching cloud of plasma is not clear, but if exoplanet studies have taught us anything, it’s that the universe is a tough place to be a planet.

Today’s attendees included Jennifer Briggs, Emily Jensen, and Tyler Wade.