Current Research

My current research is on the dynamics of tightly-packed planetary systems, such as the TRAPPIST-1 system which consists of a red dwarf star orbited by at least 7 planets which have orbits very close to their star. The most distant planet in the system is 500 times closer to its star than Neptune (the most distant planet in the Solar System) is to the Sun! The planets also have orbits that are spaced very close together. In terms of "dynamical units" (i.e. scaled by the gravitational force between planets), the TRAPPIST-1 system is four times more tightly-packed than the terrestrial planets of the inner Solar System!

As planets' orbits become closer together, the gravity between planets becomes stronger and this disturbs planets' orbits around their host star, introducing small changes that can accumulate and build up over many orbits. If planets have orbits that are too close together, these changes can lead to systems going unstable. Eventually, this can result in planets colliding, innter planets falling into their host star, or outer planets getting kicked out of the system.

The TRAPPIST-1 system is kept safe from these changes because the planets are in a resonant chain. Every time TRAPPIST-1h (the most distant planet in the system) completes 2 orbits, TRAPPIST-1g (its inner neighbour) completes roughly 3 orbits. For every 3 orbits of TRAPPIST-1g, TRAPPIST-1f completes roughly 4 orbits. For every 2 orbits of TRAPPIST-1f, TRAPPIST-1e completes roughly 3 orbits. For every 2 orbits of TRAPPIST-1e, TRAPPIST-1d completes roughly 3 orbits. For every 3 orbits of TRAPPIST-1d, TRAPPIST-1c completes roughly 5 orbits. Lastly, for every 5 orbits of TRAPPIST-1c, TRAPPIST-1b completes roughly 8 orbits.

If a tightly-packed system with multiple planets is not in a resonant chain however, the orbits of the planets can gradually change until the system goes unstable - eventually leading to the catastrophic events like collisions and ejections.

Beginning as an AST 1501 project supervised by Dr. Christa Van Laerhoven and working with Dr. Daniel Tamayo, we simulated over 16 000 systems of five Earth-mass planets in orbit around a Solar-mass star. We found that mean-motion resonances can affect the survival time of systems by several orders of magnitude. Additionally, we found that a maximum of five of Earth-mass planets can survive in the habitable zone for 10 billion years. I presented this work at the 2016 DDA Meeting.

I am continuing this research for my PhD thesis with Professor Norm Murray at the Canadian Institute for Theoretical Astrophysics (CITA).

Past Research

For my AST 1500 project I worked with Professor Kristen Menou on tidally-locked water worlds around M dwarfs. I obtained equatorial atmospheric profiles by adapting FORTRAN code which used a relaxation algorithm to converge to a solution governed by the fluid dynamics of the atmosphere.

Towards the end of 2014, I started working with Professor Catherine Johnson studying Mercury's northern cusp using MESSENGER magnetometer data. Based on earlier work conducted by Dr. Reka Winslow (see R. Winslow et al. Geophysical Research Letters, Volume 39, Issue 8), we extended the analysis to incorporate data from the entire MESSENGER mission.

For my undergraduate honours thesis in 2013 and 2014, I worked with Professor Harvey Richer and Professor Jeremy Heyl on white dwarf core crystallization in 47 Tucanae, searching for evidence of the release of latent heat. I continued working on this project over the summer using MESA to construct models of white dwarf cooling histories with varied physics. I presented a poster of my thesis work at the 15th Annual Meeting of the Northwest Section of the APS. A. C. Obertas, H. Richer, and J. Heyl. Searching for Evidence of White Dwarf Core Crystallization in 47 Tucanae. This work continued after my graduation with Ilaria Caiazzo, presenting stellar evolution models which demonstrate that the change in white dwarf cooling seen in 47 Tuc corresponds to the onset of convection.

In 2013, I worked with Dr. Michael Tandecki as an undergraduate researcher on the Francium PNC experiment at TRIUMF. My primary tasks were working with the optics for the experiment's magneto-optical trap and running simulations to examine the effects of background magnetic fields on the trap. During this position, I presented a poster at the 2013 Canadian Association of Physicists Congress. Obertas, A. C. et al. Establishing a relative frequency standard for trapping francium.

In 2012, I worked with Dr. Petr Navratil as an undergraduate researcher in the Theory Group at TRIUMF. I wrote and used FORTRAN code to study helium-helium scattering reactions. I gave a talk on this work at the 2012 Canadian Undergraduate Physics Conference.


Alysa Obertas, Ilaria Caiazzo, Jeremy Heyl, Harvey Richer, Jason Kalirai, and Pier-Emmanuel Tremblay. The onset of convective coupling and freezing in the white dwarfs of 47 Tucanae. Monthly Notices of the Royal Astronomical Society, Volume 474, Issue 1, p.677-682. February 2018.

Alysa Obertas, Christa Van Laerhoven, & Daniel Tamayo. The stability of tightly-packed, evenly-spaced systems of Earth-mass planets orbiting a Sun-like star. Icarus, Volume 293, p. 52-58. June 2017.

Daniel Tamayo, Ari Silburt, Diana Valencia, Kristen Menou, Mohamad Ali-Dib, Cristobal Petrovich, Chelsea X. Huang, Hanno Rein, Christa van Laerhoven, Adiv Paradise, Alysa Obertas, and Norman Murray. A Machine Learns to Predict the Stability of Tightly Packed Planetary Systems. The Astrophysical Journal Letters, Volume 832, Issue 2, article id. L22, 5 pp. December 2016.