Research
My research interests are in star and planet formation, meteoritics, astrobiology, asteroid hazards/mining. I use astrophysical modeling, in conjunction with observations (both astronomical and meteoritical), to determine conditions during the formation of planetary systems, including our own Solar System. I use planetary materials and astronomical spectra to search for signs of aqueous alteration of solids, exotic exoplanets, and habitable worlds. I use astrophysical modeling, in conjunction with the determination of material properties of planetary materials, to determine hazards inherent to Near Earth Objects (NEOs) and targets of sample return missions and/or mining ventures.
Phyllosilicate Emission from Protoplanetary Disks
Phyllosilicates are hydrous minerals formed by interaction between rock and liquid water and are commonly found in meteorites originating in the asteroid belt. Collisions between asteroids contribute to the zodiacal dust, which therefore reasonably could include phyllosilicates. Collisions between planetesimals in protoplanetary disks may also produce dust containing phyllosilicates. These minerals possess characteristic emission features in the mid-infrared and could be detectable in extrasolar protoplanetary disks. In order to determine whether phyllosilicates in protoplanetary disks are detectable in the infrared using instruments such as those on board the
Spitzer Space Telescope and SOFIA (Stratospheric Observatory for Infrared Astronomy), it is necessary to calculate opacities for the phyllosilicates most common in meteorites and compute the emission of radiation from a protoplanetary disk using a 2-layer radiative transfer model. We have found that phyllosilicates present at the 3% level lead to observationally significant differences in disk spectra, and should therefore be detectable using infrared observations and spectral modeling. Detection of phyllosilicates in a protoplanetary disk would be diagnostic of liquid water in planetesimals in that disk and would demonstrate similarity to our own Solar System. Additionally, phyllosilicate emission can be used to test the "waterworlds" hypothesis, which proposes that liquid water in planetesimals should correlate with the inventory of short-lived radionuclides in planetary systems, especially 26Al. We plan to examine archived data obtained with the Spitzer Space Telescope to search for the spectral signature of the presence of phyllosilicates. If such a signature is found, it would amount to an indirect detection of water in an extrasolar planetary system.Chondrule Formation
Chondrules are millimeter-sized, silicate (mostly ferromagnesian) igneous spheres found within chondritic meteorites. They are some of the oldest materials in our Solar System, having formed within a few million years of its birth. Chondrules were melted at high temperature (over 1800 K), while they were free-floating objects in the early solar nebula. Their petrology and chemistry constrain their formation, especially their thermal histories. Chondrules provide some of the most powerful constraints on conditions in the solar nebula. The chondrule formation process, despite its obvious importance, has been a mystery in the field of meteoritics for two centuries. Proposed mechanisms include interaction with the early active Sun, through jets or solar flares, melting by lightning and melting by planetesimal impacts. The most widely-accepted hypothesis, though, is that chondrules were melted in shock waves in the protoplanetary disk. A shock wave, or shock front, is a sharp discontinuity between supersonic and subsonic gas, over an area only a few molecular mean free paths thick (typically only meters in the solar nebula). The gas is slowed, compressed, and heated by the time it reaches the other side of the shock front. Solids moving with the gas are heated not only by thermal exchange upon entering the shocked region, but also by friction as they are slowed to the postshock gas speed, and by absorbing the infrared radiation emitted by other solids. The shock model of chondrule formation appears able to resolve the chondrule formation mystery, because it makes several detailed predictions about chondrule formation that are largely borne out by observation and experimentation, especially regarding chondrule thermal histories. My work involves developing and testing models, in which chondrule precursors are melted by passage through solar nebula shocks. I have also recently performed analytical work measuring the properties of chondrules, in order to further constrain models of their formation.
Here is an animation of a bow shock around a large planetary embryo.
Here is an animation I produced which shows the heating of chondrules and dust as they pass through shocked gas, and subsequent cooling.