Current and Recent Projects


How would Planet 9 affect the Kuiper Belt?


I've been involved in several related projects on Planet 9, which was proposed by Sheppard & Trujillo (2014) and Batygin & Brown (2016) to explain apparent clustering in the orbits of known trans-Neptunian Objects (TNOs, also called Kuiper Belt Objects).

In Lawler et al. 2017 we ran large simulations to see how Planet 9 would affect the orbits of the Kuiper Belt over the age of the Solar System. We found that Planet 9 would raise perihelia and inclinations (make their orbits more distant and more tilted), but that we wouldn't expect to see this in current large surveys because these TNOs are so hard to detect. We also did not find any evidence for clustering of orbital angles caused by Planet 9.


In Shankman et al. 2017 we ran large simulations specifically to look at how Planet 9 would cause clustering of orbits. We found that this clustering does not persist for long, even among currently known TNOs. ***Animation available here***.


Overall, our simulations show that the evidence that is claimed to require an additional planet in the solar system is weak.


Explaining the Weird Orbit of Fomalhaut b


Fomalhaut b is one of the first exoplanet candidates to be directly imaged (Kalas et al. 2008). Recent astrometry has shown that the orbit is highly eccentric, and Fom b may even cross the debris ring that is also present in the system.


In Lawler et al. 2015 we explore the likelihood of catastrophic collisions within the Fomalhaut disk, using our Kuiper Belt as a starting point. We find that the rate of catastrophic disruptions of 100 km bodies (large enough to reproduce observations of Fom b as a dust cloud only), is high enough that at least one Fom b-like cloud should be visible at any given moment.


Two testable predictions from this model, within the next decade: 1) Fom b should disperse and either become resolved or fade away, and 2) another dust cloud in a different part of the disk should also become visible.


The Disk-Planet System of the Sun-like Star tau Ceti


tau Ceti is a nearby Sun-like star that hosts a disk (Greaves et al. 2004) and a possible multiplanet system (Tuomi et al. 2012). In Lawler et al. 2014, we use Herschel data and find that the disk is very wide, consistent with dust stretching from asteroid belt distances to the outer edge of the Kuiper belt. We were unable to gain any constraints on the orbits of the possible planets due to the low resolution of Herschel.


We have taken advantage of the very high resolution offered by ALMA and obtained data which we hope will help to constrain the inner edge of the disk. This will help to validate or rule out the tightly-packed system of super-Earths that has been proposed in the inner parts of the tau Ceti system.


The Outer Solar System Origins Survey


I am a member of the Outer Solar System Origins Survey (OSSOS), and was previously a member of the Canada-France Ecliptic Plane Survey (CFEPS), which finished in 2009. These ambitious surveys on the Canada-France Hawaii Telescope have and will discover many objects in the Kuiper Belt. Most importantly, these surveys are well-calibrated, so observations can be debiased, and the true number and distribution of objects within each sub-population can be measured.


Part of my PhD thesis was to measure the populations and orbital distributions within several of the mean-motion resonances with Neptune. This provides powerful constraints on models of giant planet migration in our Solar System's early history. I hope to repeat this analysis more in-depth as OSSOS finds more resonant Kuiper Belt Objects.