James Owen

In the last few years we have been able to observe the planet forming environments (protoplanetary discs) with unprecedented resolution and sensitivity. This revolution has primarily been driven by the ALMA telescope, and has produced spectacular images of protoplanetary discs.
Caption: ALMA images of planet forming discs, image credit ESO/NAOJ/NRAO.

One of the mysteries is the origin of highly asymmetric discs (bottom right panel of the Figure). An explanation is that these discs contain anti-cyclonic vortices which are trapping large quantities of small solid particles (mm-sized dust particles). However, the question remains: how do you get large scale vorticies in protoplanetary discs? In Owen and Kollmeier 2017, we suggested that thermal feedback from a forming planet could provide the necessary source of vorticity to form large scale vorticies (see video below). This project will involve developing this model further, including more detailed planet formation calculations and computer simulations of vortex formation and destruction. A detailed description of the project can be found here.

The discovery of exoplanets ranks as one of the most exciting advances in astronomy. However the types and range of exoplanets we have discovered go far beyond what our theories of planet formation predict. The most surprising result of the last five years, primarily produced by the Kepler mission, has be the discovery of a dominant class new exoplanet. These planets have radii between that of Earth and Neptune, yet have orbital periods inside that of Mercury. Even more unusual is that many of these planets have compositions of a solid core surrounded by a Hydrogen-rich atmosphere that contributes a few percent to the planets mass. These planets are not predicted by our standard theories of planet formation, that have been conditioned on the solar-system (see Figure).
Caption: Observed exoplanets from exoplanets.org (Left). Previous theoretical prediction of the exoplanet distribution (Right, Ida and Lin 2008). Note that the gap in the theoretical prediction for close-in planets with masses in the range 1-100 Earth masses is completely filled by exoplanets. The difference between the observations and theoretical predictions is not well understood.

Protoplanetary discs live for about 10 million years before being dispersed rapidly and the observed exoplanets are billions of years old. Therefore planet formation occurs rapidly and then the planets evolve into the population we see today. The fact these planets are so close to their parent stars means there atmospheres are strongly irradiated. This extreme heating can cause the atmospheres of these exoplanets to hydrodynamically flow away. This planet ``evaporation'' causes these planets to lose mass over their lifetimes. This hydrodynamic outflow is shown in the video below.
A lot of this mass-loss occurs during the early phases of the planet's lifetime. While the planet is forming its atmosphere is pressure confined within the protoplanetary disc, yet when the gas disc disperses this pressure confinement disappears. This decompression causes the planet's atmosphere to expand and escape the planet's gravitational well. In Owen and Wu 2016 we should this decompression can have dramatic consequences on the evolution of a planet's atmosphere. This project is to study this process in more detail using a combination of analytic and numerical methods. A detailed description of the project can be found here.

Apart from the above projects I have interests in accretion disc physics, star formation, stellar rotation, circumplanetary discs, planet-star/planet-disc interactions and giant planet formation. If you have interests in these areas and have ideas for potential projects please get in touch.