Research

My research career focused on the discovery and characterization of exoplanets — especially cold, long-period gas giants — alongside related work in Solar System planetary science. The projects below are the main threads of that work.

Cold Gas Giant transiting Exoplanets

Jupiter and Saturn have long fascinated us, but their counterparts around other stars are difficult to study. Cold, long-period gas giants are hard to discover as transiting exoplanets — which we detect indirectly as they pass in front of their host stars — and harder still to characterize. Yet their atmospheres hold clues to how planetary systems form and evolve.

My work centered on finding these planets and measuring their masses, orbits, and atmospheres. Because their transits can occur only once a year or less, every transit counts. I focused on mass measurements, on coordinating the follow-up needed to catch these rare events, and on simulating how their atmospheres might one day be characterized. This work drew on an array of telescopes, including the Lowell Discovery Telescope (formerly the Discovery Channel Telescope), the Spitzer Space Telescope, the Keck I telescope, Kepler, and the Transiting Exoplanet Survey Satellite (TESS), along with a network of smaller observatories around the world.

Radial Velocity Characterization

Many exoplanet masses are measured with the radial velocity (RV), or "wobble," method, which tracks the small back-and-forth motion of a star's spectral lines as an orbiting planet tugs on it. RV is especially powerful for transiting planets: combining the radius (from the transit) with the mass (from RV) reveals far more about a planet — its likely composition, interior, and formation history — than either measurement alone. 

The longest-period transiting planets, though, mostly lacked mass measurements, because long-term RV surveys rarely targeted them. To close that gap, I led long-term RV monitoring campaigns on the Keck I telescope at W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory, which together became the Giant Outer Transiting Exoplanet Mass (GOT 'EM) Survey. The survey produced a series of papers:

• GOT 'EM I — Confirmation of an eccentric, cool Jupiter with an interior Earth-sized planet orbiting Kepler-1514 (Dalba et al. 2021, AJ)

• GOT 'EM II — Discovery of a "failed" hot Jupiter on a 2.7-year, highly eccentric orbit (Dalba et al. 2021, AJ)

• GOT 'EM III — Recovery and confirmation of a temperate, mildly eccentric, single-transit Jupiter orbiting TOI-2010 (Mann, Dalba et al. 2023, AJ)

• GOT 'EM IV — Long-term Doppler spectroscopy for 11 stars thought to host cool giant exoplanets (Dalba et al. 2024, ApJS)

• GOT 'EM V — Two giant planets in Kepler-511, but only one ran away (Chachan, Dalba et al. 2025, AJ)

• GOT 'EM VI — Confirmation of a long-period giant planet discovered with a single TESS transit (Essack, Dragomir, Dalba et al. 2025, AJ)

Transit Recovery

Most known transiting exoplanets have short orbital periods — a bias of the transit method, since planets close to their stars are far more likely to line up and transit from our viewpoint. Long-baseline surveys like Kepler did turn up a handful of long-period transiting planets more like those in our own Solar System.

But the difficulty doesn't end at discovery. Gravitational interactions with other bodies in a system can shift the timing of a planet's transits, making future events hard to predict — and risky to chase with scarce telescope time. I worked on recovery efforts to improve the accuracy and precision of predicted transit times for long-period planets. Two published examples show what that work involved: Kepler-167e (2019, ApJL) and Kepler-421b (2016, ApJL).

atmospheric refraction and transiting Exoplanets

Refraction is one of the most familiar behaviors of light, and it turns out to matter for exoplanet transits. As part of my PhD thesis, I studied how, just before or after a planet transits, some of the star's light can be refracted by the planet's atmosphere into a distant observer's line of sight — producing a faint secondary image of the star, a kind of mirage, that slightly increases the system's total brightness. By modeling that brightening and identifying which systems would show it most clearly, I demonstrated one way refraction could reveal information about exoplanet atmospheres — and even help detect planets that do not transit at all. This work was published in the Astrophysical Journal (Dalba 2017).

For this project I also built RETrO (Refraction in Exoplanet Transit Observations), an open-source ray-tracing code that models refraction in an exoplanet context. It remains freely available on GitHub.

solar system science from occultations

A planet is a planet, near or far. I have always believed the future of exoplanet science depends on carrying forward decades of Solar System planetary science, and much of my work lived at that intersection — drawing on datasets from the Cassini mission and using occultations, natural and human-made, to probe planetary atmospheres.

Titan's ionosphere from radio occultations. In a radio occultation, a spacecraft sends an ultra-stable signal to an Earth-based station as it passes behind a body like Titan. Working with Prof. Paul Withers, I processed the full set of Cassini radio occultations of Titan to produce electron-density profiles of its ionosphere — extracting a millihertz signal carried at gigahertz frequencies. This work was published in the Journal of Geophysical Research: Space Physics (Dalba & Withers 2019), and the approach later extended to Saturn's ionosphere (Tamburo et al. 2023).

Saturn as a transiting exoplanet. Using Cassini data, I explored what we could learn from a Saturn-twin exoplanet. Despite being cold and cloudy, such a world turns out to be surprisingly amenable to atmospheric characterization — observatories like the Hubble Space Telescope and James Webb Space Telescope could probe features such as methane content and disequilibrium chemistry. This work was published in the Astrophysical Journal (Dalba et al. 2015) and drew some press coverage; see the Media Coverage page.