Dr. Sam Lawler's Astronomy Research

Research Group

Current Students:

Lowell Peltier (PhD@UVic, co-supervising), Jaidyn Draper (BSc Honours U. Regina and undergrad research assistant)

Former Students:

Rosemary Dorsey (PhD@Canterbury U., New Zealand 2025, co-supervised), Cameron Semenchuck (BSc Honours@UVic 2024), Maelle Magnan (BSc@U. of Toronto, summer research student 2023), Madison Blatchford (BSc Honours U. Regina 2023), Breanna Crompvoets (BSc Honours U. Regina 2021), Emily Crumley (U. Regina research assistant 2021-22), Mriana Yadkoo (research co-op 2020, research student 2024), AbdelRahman Rabaa (research co-op 2020)

Current and Recent Projects

Satellite pollution

Below are movies of the brightness and positions of future satellites at different latitudes and times of year, made from the simulations in Lawler, Boley, & Rein (2022, The Astrophysical Journal). Note that this was before the orbital data centre rush started by SpaceX asking for one MILLION satellites. Preliminary results from simulations on those are here, but we are actively working on more detailed simulations of orbital data centre megaconstellations.

The code to make these simulations is open-source and publicly available in this github repository, and a simple webapp is available here. There is also an Apple device app available in the Apple app store that is based on our simulations.

The movies below are mainly the latitudes of cities where I have given (mostly remote) talks about satellite pollution. Want to see a different latitue?

From north to south, the simulations I've put together (and an example city or few close to that latitude):

Latitude 54 degrees North (example cities: Edmonton, Dublin, Hamburg)

Latitude 50 degrees North (example cities: Regina, Vancouver, Brussels, Prague)

Latitude 48 degrees North (example cities: Seattle, Paris, Munich, Ulaanbaatar)

Latitude 46 degrees North (example cities: Portland, Milan, Harbin)

Latitude 44 degrees North (southern Ontario, Florence, Sapporo)

Latitude 42 degrees North (Boston, Chicago, Barcelona, Rome, Tbilisi)

Latitude 40 degrees North (Boulder, Ankara, Beijing)

Latitude 39 degrees North (Washington DC, Lisbon, Athens, Pyongyang)

Latitude 34 degrees North (Los Angeles, Atlanta, Casablanca, Islamabad, Osaka)>

Latitude 20 degrees North (Hilo, Mexico City, Mumbai, Hanoi)

Latitude 30 degrees South (Vera Rubin Observatory - Chile, Durban, Perth)

Latitude 44 degrees South (Christchurch, New Zealand)

Kuiper Belt Discovery and Dynamics

The CLASSY Survey

I'm co-PI of a Large Program on the Canada-France-Hawaii Telescope that has used almost 400 hours of observing between 2022-2025 to discover some of the smallest and most distant Kuiper Belt Objects. Discoveries are ongoing, testing the theory of "clustered eTNOs".

The LiDO Survey

I'm co-PI of a program on the Canada-France-Hawaii Telescope discovered 140 moderately high inclination Kuiper Belt Objects.

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.

New JWST data has shown that there is a new dust cloud, and that Fomalhaut b is gone!

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.