Probing carbon chemistry and dust in the planet-forming zones of brown dwarf disks

Brown dwarfs (BDs) are faint, sub-stellar objects and are the link between stars and planets. Low-mass stars tend to have abundant terrestrial planets and the formation and evolution of BDs themselves may be a window into giant planet formation. In contrast to higher-mass disks, BD disks are optically thinner in the mid-infrared giving us access to the gas and dust composition closer to the disk midplane where planets are forming, making them unique objects to study. Spitzer-IRS spectra of BD disks showed generally weak silicate features indicative of dust settling and gas detections that point to a high carbon-to-oxygen (C/O) ratio. The high C/O ratio may be due to 1) oxygen locked up in ice in the outer disk, 2) a carbon-rich chemistry close to the midplane that is only observable in disks with settled dust, and/or 3) the destruction of carbonaceous grains. Any of these scenarios would have a profound impact on the composition of forming planets and JWST-MIRI MRS data are crucial for studying the gas and dust in the planet-forming zones, particularly in these faint targets. Cycle 1 observations are largely focused on higher-mass sources, leaving a need for observations of BDs. We propose to get high sensitivity (SNR>100) spectra for a large and representative sample of 15 low-mass targets to catalog the chemical inventory and study the connection between the gas and dust properties. These targets span a range of ages and, based on low-resolution IRS data, show diversity in silicate feature strength and shape, indicating large variations in the dust properties. We will be able to put these systems into context with higher-mass stars that are observed in larger numbers.