Relevant Degree Programs
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2021)
The Trans-Neptunian objects (TNOs) preserve evidence of planet building processes in their orbital and size distributions. While all populations show steep size distributions for large objects, recently a relative deficit of Neptunian Trojans and scattering objects with diameters D99% confidence. The fact that three independent samples of three different populations show this trend suggests that it is a real feature, possibly shared by all hot TNO populations as a remnant of ''born big'' planetesimal formation processes. We surmise the existence of 9000 ± 3000 Plutinos with absolute magnitude Hr ≤ 8.66 and estimate 37000 +12000/-10000 Plutinos with Hr ≤ 10.0 (95% confidence ranges). Our survey also discovered one temporary Uranian Trojan, one temporary Neptunian Trojan and one stable Neptunian Trojan.With these discoveries, combined with our survey characteristics, we derive populations of 110 +500/-100, 210 +900/-200 and 150 +600/-140 for these populations, respectively, with Hr ≤ 10.0.With such approximately equal numbers, the temporary Neptunian Trojans cannot be previously stable Trojans that happen to be escaping the resonance now; they must be captured from another reservoir. Our population estimate also reveals that the Neptunian Trojans are less numerous than the main belt asteroids (semi-major axis 2.06
Studying the orbital dynamics of small body populations in the Solar System allows us to understand both their current population and past orbital structure. Planet-crossing populations can also provide impact speeds and probabilities, and when coupled to cratering histories of solid bodies can provide planetary surface ages.The Wide-field Infrared Survey Explorer Near-Earth Object (NEOWISE) detections of the near-Earth object (NEO) orbital distributions (Mainzer et al. 2012) are used to illustrate that a pure-gravity NEO orbital model (Greenstreet et al. 2012) is not rejectable (at >99% confidence). Thus, no non-gravitational physics is required to model the NEO orbital distribution.We discovered in the NEO model numerical integrations the unexpected production of retrograde orbits from main asteroid belt sources, estimating that ~0.1% of the steady-state NEO population is on retrograde orbits. These retrograde near-Earth asteroids (NEAs) may answer two outstanding questions in the literature: the origin of two known MPC NEOs with asteroidal designations on retrograde orbits and the origin of high-strength, high-velocity meteoroids on retrograde orbits.Moving to the outer Solar System, we constructed a Centaur (a_Jupiter
The small body populations within a planetary system give information about the planet formation and migration history of the system. In our Solar System, we study these bodies (asteroids, comets, and trans-Neptunian objects), by directly observing them in reflected light. In other solar systems, dust traces the position of the planetesimal belts that produce it, and is observed as an excess above the stellar flux in the infrared. The dust is visible and not the planetesimals because of the much greater cross-sectional surface area of a swarm of dust particles. In this thesis, both leftover large planetesimals in our Solar System and dust around other stars are investigated.Data from the Canada-France Ecliptic Plane Survey (CFEPS) are used to measure the absolute populations of trans Neptunian objects (TNOs) in mean-motion resonances with Neptune, as well as constrain the internal orbital element distributions. Detection biases play a critical role because phase relationships with Neptune make object discovery more likely at certain longitudes. The plutinos (objects in the 3:2 resonance) are given particular attention because the presence of the secular Kozai resonance within the mean-motion resonance causes different detection biases that need to be accounted for to properly debias surveys that include detections of plutinos. Because the TNOs that are trapped in mean-motion resonances with Neptune were likely emplaced there during planet migration late in the giant planet formation process, the structure within and relative populations of the resonances should be a diagnostic of the timescale and method of giant planet migration. Exoplanet systems that host several rocky planets are those that did not experience giant planet migration, and thus are likely to host planetesimal belts which should be detectable as debris disks. The Kepler Mission has detected a host of such systems, and we use data from the Wide-field Infrared Survey Explorer (WISE) Mission to search for debris disks around these stars. Though we tentatively detect more excesses toward these stars than would be expected, contamination from warm dust in the Milky Way Galaxy makes detection unreliable for these systems, and will have to await future infrared space telescopes.
Master's Student Supervision (2010 - 2020)
Out beyond the giant planets is a collection of bodies left over from planet formation. Theobjects that are just beyond Neptune are well studied compared to those that journey hundredsof au away; all such objects have been observed inside 100 au. We use a deep narrow surveyand an uncommon technique to search for objects currently at large heliocentric distances.Using data from the Outer Solar System Origins Survey (OSSOS), which covered ∼160 squaredegrees down to r ∼ 25, we searched for objects beyond 300 au. To find such objects wecreated a catalogue of all of the objects that were stationary of the astronomical seeing in threeimages taken over 2 hours. We then examined the stationary objects that were no longer theredays/weeks/months before and after the three images. Although other astronomical phenomenalike supernovae where discovered, no slow moving solar system object was found. From the nulldetection and using a survey simulator we obtain a 95% upper limit to the number of dwarfplanets (-3 > H > 2) in the distant solar system, 1100 (+1700/−800). To our knowledge this is the first published limit for dwarf planets beyond several hundred au.
We present a joint analysis of the Canada France Ecliptic Plane Survey'sscattering objects, and the Kaib et al. (2011b) orbital model, measuring thescattering objects' size distribution. Scattering objects are Trans-Neptunianobjects which are strongly interacting with Neptune, having scattering encounters which change their semimajor axes on short dynamical timescales.We reject a single power-law distribution at the 99% level, and find thata dearth of small objects is required. We present a novel parameterisationof a divot size distribution, which rises as a single power-law to a precipitousdrop, then recovers as another single power-law of potentially differentslope. We constrain the form of such a divot distribution, and find that divotsare preferred over "knee" size distributions, which are found elsewherein the literature for different populations. We present our preferred divotscenario, which rises as a single power-law of logarithmic slope α = 0.8 asabsolute Hg magnitudes increase to sizes corresponding to D ~ 100 km, thendropping by a factor of about 6 in differential number, followed by anothersingle power-law of logarithmic slope α = 0.5. Our interpretation is thatthis feature arose from the size distribution made by planetesimal formationand is now "frozen in" to the "hot" populations of the outer Solar System.From this we estimate there are 2‧10⁹ scattering objects with Hg
Canada's Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with semimajor axis a