Confirmation of Candidature - Candidate : Ava Morrissey

Over the duration of my PhD, I will investigate how small exoplanets evolve around young stars. The atmospheres of planets forming around young stars get moulded by the intense XUV flux radiating from the star. This period of relentless irradiation from the host star lasts for around 100 million years post-formation, with an exponential decline hereafter. During this period, the XUV irradiation will "blow off" species from the upper atmosphere of the orbiting planet. Light species, such as hydrogen and helium, are the most susceptible to this mass-loss mechanism as they require relatively less energy to be accelerated to the planet's atmosphere's escape velocity where they will then "evaporate" into space. This process is not intrinsically an extra-solar one. Previous research showed that our Earth underwent a similar evaporation process 4 billion years ago while it was forming and evolving. Earth's hydrogen molecules and helium atoms were swept away by the solar wind early in the Hadeon era, leaving the planet with a secondary atmosphere of methane, ammonia, water vapour and trace amounts of nitrogen and carbon dioxide. By observing exoplanets that are undergoing mass loss we can develop a deeper understanding of the mechanisms that cause it, and the timescales that they occur over. We are probing the atmosphere of HIP94235b, a 100Myr sub-Neptune orbiting closely around a Sun-like star. We believe that this planet-star system holds the correct conditions to host an evaporating planetary atmosphere. We are making use of HST's STIS and VLT's CRIRES+ to probe the hydrogen and helium lines of this transiting planet in search of signals of photoevaporation. By studying the velocity profiles of these species, we will infer the speed at which mass loss happens for these systems. We hope to probe similar atmospheres in the NIR to better understand the heavier secondary atmospheres that get left behind. Will they resemble similar chemical species as our Earth's did? Are there other mechanisms at play that we can observe? We have proposed for JWST NIRSpec time to examine the atmosphere of this same planet to try and develop a broader understanding of photoevaporating atmospheres as a whole.

For more information, please email the Graduate Research School or phone 0746 31 1088.