Research

Cold, Long-Period Transiting Exoplanets

Jupiter and Saturn have long been subjects of human fascination. Unfortunately, in terms of transiting exoplanets—which we observe indirectly when they pass on front of their host starsthese types of cold, long-period, gas giants are hard to discover and even harder to fully characterize. Yet their atmospheres hold precious clues that may help us better understand how planetary systems form and evolve in time.

Saturn in rather alien (false) colors! Image credit: NASA/JPL/Univ. of AZ
Saturn in rather alien (false) colors! Image credit: NASA/JPL/Univ. of AZ

I am particularly interested in finding these types of planets and characterizing their orbits and atmospheres. This can be especially difficult if transit events only happen once a year (or even less frequently). What this means is that every transit counts! I recently conducted an observing campaign with the Discovery Channel Telescope to observe the partial transit of Kepler-421b—a Neptune-sized exoplanet that only orbits its host star once every 704 days! The results of this project are published in the Astrophysical Journal Letters. Take a look at the paper on the arXiv here: http://arxiv.org/abs/1606.09246

Atmospheric Refraction and Transiting Exoplanets

crescents
Each of the colorful crescents is a mirage of the star (left, big red circle) in the atmosphere of the planet (black circles) at different times leading up to transit.

Refraction is one of the most fundamental behaviors of light and it is indeed something we encounter in our every-day lives. In support of my PhD thesis, I conducted theoretical investigations of this process in terms of transit observations of long-period exoplanets. It turns out that before or after an exoplanet transits its host star, some of the stars light can be refracted into a distant observer’s line of sight by the planetary atmosphere. The end result of this is a secondary image of the host star in the exoplanet’s atmosphere—a.k.a. a mirage! This mirage causes the total flux of the unresolved star system to increase just a little. By modeling that brightness increase and understanding which types of planetary systems would clearly display such a phenomenon, I revealed one way in which refraction can help us learn about exoplanet atmospheres. It is also a method of discovery exoplanets that do not transit their host stars.

This result are published in the Astrophysical Journal, and you can read it on the arXiv here: https://arxiv.org/abs/1709.06991. I also gave a talk on this work in the Astronomy Department at BU recently.

BTW: For this project, I developed a thorough ray tracing code that includes refraction in an exoplanet context. It’s call RETrO: Refraction in Exoplanet Transit Observations. I made the custom code available to anyone on github: https://github.com/pdalba/retro. If you find yourself in need of ray tracing simulations involving refraction, contact me!

Exoplanets and Our Solar System

The sun "setting" behind Saturn as seen from the Cassini Spacecraft. (Image courtesy of NASA/JPL/SSI)
The sun “setting” behind Saturn as seen from the Cassini Spacecraft. (Image courtesy of NASA/JPL-Caltech/SSI)

I used observations from NASA’s Cassini Spacecraft to explore what we could learn if we found and characterized a Saturn-twin exoplanet. As it turns out, despite being very cold and cloudy, the atmosphere of a Saturn-like exoplanet is exceptionally amenable characterization! Current and future observatories such as the Hubble Space Telescope and the James Webb Space Telescope will have the capabilities to probe these atmospheres to learn about methane content and even amazing disequilibrium processes such as photochemistry!

This work was published in the Astrophysical Journal in October 2015, and it also received some press attention. Take a look at the articles listed in the Media Coverage section of my website.

Disintegrating Planetesimals Orbiting a White Dwarf Star

I am also involved in a campaign to observe and characterize temporal variations in the brightness of white dwarf WD1145+017. According to the discovery paper and our subsequent follow-up article, this exotic system may contain a disintegrating minor planet that causes asymmetric dips in brightness that vary in size, duration and period! Our investigations of this interesting object may shed light on the properties of white dwarf stars, the eventual end-state of our Sun.

Previous Research

While working at JPL, I completed a variety of research projects related to NASA missions such as Cassini, Dawn, and New Horizons with the help of Dr. Bonnie Buratti. We investigated Titan’s precipitation and methanological cycle, probed the surface texture of Saturn’s icy moons,  studied the color differences seen on the surface of the minor-planet 4 Vesta, and conducted photometric observations of Pluto in search of signatures of atmospheric volatile transport. Please see my Publications page for links to articles and abstracts produced from this work.

As an undergraduate researcher at UC Berkeley, I performed a theoretical study of externally-fed accretion onto protostars with Dr. Steven Stahler, and conducted photometric observations of multiple asteroid systems with Dr. Franck Marchis. Again, please reference my Publications page for more detailed information on these projects.

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