About me

I recently received my PhD in astronomy & astrophysics from the University of Arizona. My research in Daniel Apai's group centered on topics related to habitable exoplanets and astrobiology, with a primary focus of enabling future efforts to discover and characterize potentially Earth-like planets in the solar neighborhood. I also spent over fifty nights at telescopes in Arizona searching for transiting planets around nearby low-mass stars.

Publications

My research interests revolve around the detection and characterization of habitable extrasolar planets. You can find a full list of my publications and presentations on ADS or Google Scholar. Here are a few of my most recent first-author papers:

Bioverse: a simulation framework to assess the statistical power of future biosignature surveys

Bixel & Apai (2021)

I have developed a Python-based framework for evaluating the ability of next-generation space telescopes to conduct statistical studies of habitable exoplanets. In this paper, I present this framework and use it to study two questions: "How can we determine the location and width of the habitable zone?" and "How can we study the evolution of oxygen on Earth-like planets?". The ability to answer statistical questions such as these is a crucial requirement for next-generation life-finding observations.

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Testing Earth-like Atmospheric Evolution on Exo-Earths

Bixel & Apai (2020)

Earth's atmosphere has evolved over billions of years, from a primordial oxygen-free state to its present oxygen-rich state which supports the complex life. In this paper, we suggest that such an evolutionary pattern might be common for inhabited Earth-like planets, and investigate whether next-generation observatories could be used to test this hypothesis.

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Identifying Exo-Earth Candidates in Direct Imaging Data

Bixel & Apai (2020)

Future space telescopes could be able to directly image nearby solar systems in search of habitable planets and life beyond the Earth. Their primary focus will be to characterize the atmospheres of approximately Earth-sized planets in the habitable zone - or "exo-Earth candidates". However, the number of non-habitable planets outnumbers exo-Earth candidates by nearly a factor of ten! In this paper, we present a Bayesian framework which uses Kepler statistics to classify newly detected planets according to their most likely size and orbit. We show that by using our framework, one could greatly increase the follow-up observation efficiency of a future space-based direct imaging survey.

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Transmission Spectroscopy of the Hot Jupiter WASP-4b

Bixel et al. (2019)

Transit spectroscopy has been successfully employed to study the atmospheric makeup of "hot Jupiter" exoplanets for several years. However, the evidence increasingly shows that features on the stellar surface (including sunspots and faculae) can complicate these results. We assess the transit spectrum of WASP-4b by jointly modelling the impact of the atmosphere and the star on our data, finding no evidence for strong absorption or scattering features. We also measure the size and temperature of cool spot-like regions on the surface which were occulted by the planet during transit. These data were taken as part of the ACCESS Survey using the Magellan-Baade telescope at Las Campanas Observatory, where I've had the opportunity to travel for multiple observing runs.

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Probabilistic Constraints on the Mass and Composition of Proxima b

Bixel & Apai (2017)

Proxima Centauri b was discovered in the habitable zone of our nearest stellar neighbor in 2016, and instantly became a promising target in the search for life beyond Earth. Theorists published in-depth studies of its evolution and habitability while the planet was portrayed in artists' conceptions as a terrestrial, potentially Earth-like world. However, among the few measurements which astronomers could make, no direct constraints were available on the planet's composition - meaning it could resememble a non-habitable "mini-Neptune" instead of a "super-Earth". In this paper, we synthesized existing statistics on the sizes and masses of planets orbiting low-mass stars to directly compute the likelihood that Proxima Centauri b was a terrestrial planet. We found this to be highly likely, but not certain - and cautioned that this ambiguity could be substantial for planets discovered in the future.

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Contact Me

The best way to reach me is to email me. You can also message me on LinkedIn.