Brown dwarfs are often referred to as "failed stars."  Because they fall between planets and stars in terms of mass, it is often unclear which population they may be more similar to.  Theoretical models of their interiors help, but observations have revealed a great deal of complexity in their behavior.  While their infrared and to a lesser extent, optical, emissions enable us to understand the chemistry and dynamics of their atmospheres, clues about their interiors and magnetism had been sorely lacking.  Happily, radio observations allow us to probe these properties, as well as explore their nearby environments.

My team has made several important discoveries in the field of brown dwarf astrophysics, including the discovery of the first radio emitting methane brown dwarf, the potential discovery of the most rapidly rotating brown dwarf, and the potential discovery that they may undergo periodic magnetic field reversals.  However, there is still much work to be done, including how their radio emissions are caused, why so few seem to emit in the radio, and whether or not they have orbiting companions that contribute to the emission.  My team continues to explore these questions.

Since the discovery of planets outside our solar system in 1992 by Alex Wolszczan, astrophysical research has discovered over 5,000 exoplanet candidates.  Their orbital properties have been relatively easy to determine, and with the increased usage of the transit method, their bulk densities, atmospheric compositions, and temperatures are also being determined.  But as with brown dwarfs, their interior structures and magnetic properties remain unknown.  However, exoplanets close to their host stars may interact with them in a way that reveals these properties.  The magnetic field of the exoplanet may get entangled with the host star's field, resulting in flares, starspots, and other energetic phenomenon that may be detected throughout the electromagnetic spectrum from radio to X-rays.  In our ROME (Radio Observations of Magnetized Exoplanets) series, my team reports on our search for the signatures of this type of interaction.

Once enough brown dwarf magnetic fields were detected and characterized, it seemed that patterns began to emerge in their behavior.  The radio emissions from some sources seemed to change their orientation, implying changes in the underlying global magnetic field.  Other brown dwarfs seemed to show a pattern of waxing and waning magnetism, which resembles the solar sunspot cycle.  The study of this phenomenon and its relationship with with the solar magnetic field motivates my team to study the inner workings of the dynamos of these objects that generate their magnetic fields.  My team brings together observational and theoretical methods to try to understand this mysterious behavior.

My initial paper on this work was published in The Astrophysical Journal Letters, and featured in the American Astronomical Society's Nova publication of significant and innovative results.

An early focus of my research career was impact studies with Josh Colwell (UCF) and Paul Feldman (JHU).  With Josh, I had the opportunity to plan Cassini ring occultation observations, and probe the production of spokes in Saturn's B ring.  We also analyzed low velocity impacts into various types of regolith, which now has implications for planet formation.  Later, in 2005 I joined a team that conducted Hubble Space Telescope observations of the Deep Impact into Comet Tempel 1.  The images I created and analyzed from the data are at left, and were featured on on the cover of the March 2007 issue of Icarus.  In the future, I hope to return to updating the simulations I made of the Saturn spokes with the new Cassini data.

In 2013, I worked with a team at JPL to devise a mission to study the Trojan asteroids around Jupiter, in order to determine if their properties are consistent with the Nice model of solar system rearrangement.  If so, this would indicate that the Late Heavy Bombardment that battered the inner solar system with immense impacts, including on the Earth and Moon, was instigated by gravitational instability among the gas giants.  The Lucy mission, which follows from our design study, may help us learn the answer.

One of the more rewarding projects I worked on was an interdisciplinary collaboration among members of Penn State's meteorology (Hans Verlinde, Eugene Clothiaux, Scott Richardson, Guo Yu, Jennifer VanDerHorn), electrical engineering (Kultegin Aydin, Giovanni Botta), and astrophysics (me) departments.  Our team developed methods and algorithms to model the radar returns from ice crystal aggregates, and to automatically detect and measure the water content of ice crystal aggregates collected in situ in Alaska.  Our goal was to determine how radar returns from snowstorms correlated with precipitation, in order to understand how climate change affected arctic precipitation.  It was amazing to see the skills that everyone brought to the team, and how much we could accomplish when we put our heads together!