Joshua Lothringer
PhD Candidate in Planetary Science
Lunar and Planetary Laboratory, University of Arizona

“Astronomy compels the soul to look upwards and leads us from this world to another.”



I observe and model the atmospheres of exoplanets, both big and small.

In my latest paper, we self-consistently model the atmospheres of ultra-hot Jupiters (>2000 K) for the first time. We use the PHOENIX atmosphere model, which has an extensive opacity database from the UV to the far-IR. We found that atomic metals and metal hydrides can absorb enough irradiation to produce large temperature inversions in planets hotter than 2500 K, without the need for TiO or VO. We also found that thermal dissociation and H- opacity are capable of muting the 1.4 micron water feature in the secondary eclipses spectra of these ultra-hot Jupiters. There's a lot more in the paper so check it out here!

I also recently published an article in the Astronomical Journal about HST/STIS transit observations of warm-Neptune GJ 436b. Our transit spectrum from 0.5-1 micron agree with the previous interpretation that GJ 436b is a high metallicity, potentially cloudy world (Morley et al. 2017). Using photometric monitoring from Tennessee State University's APT telescope, we constrained the rotation period of the host star, GJ 436, to be 44.1 days and the activity cycle to be approximately 7.4 years, similar to other M-dwarfs of moderate age. Curiously, GJ 436 does not get redder as it gets dimmer, as one would expect if star spots were dominating the variability, suggesting an interplay between star spots and stellar plages. We also find evidence for a jump in transit depth at 0.8 microns in the transmission spectra of GJ 436b and HAT-P-26b; however, its cause could be instrumental or astropysical.

Other projects I'm working on include the MMT Exoplanet Atmosphere SURvEy (MEASURE), led by Jayne Birkby, using MMT's ARIES infrared eschelle spectrograph to identify molecular signatures in the atmospheres of short period hot Jupiters using high dispersion spectroscopy. Apart from actually taking the data, I am modeling these planets using the PHOENIX atmosphere code. I am also a part of several space telescope collaborations looking at hot Jupiter albedos and super-Earth and sub-Neptune optical and near-infrared spectra, as well as being a part of the transiting exoplanet community's JWST Early Release Science data challenge working group.

In addition to my research, I enjoy participating in public outreach. Public talks I've given include to the Tucson Amateur Astronomy Association, the Flandrau Planetarium, and my sister's school in Muscat, Oman.

Header: Exo-Resonance- For two planets in a resonance, if you draw a line between them thorughout their orbit, complex geometric patterns emerge. Left: 55 Cancri b & c. Center: Venus & Earth. Right: Kepler 10 c & d. This work won 1st place in the Data Art category at the 2015 The Art of Planetary Science.