The protoplanetary disk around the M4 star RECX 5: Witnessing the influence of planet formation?

We present Spitzer Space Telescope low-resolution spectroscopy of the protoplanetary disk around the M4 star RECX 5, a low-mass member of the ≈8 Myr old η Chamaeleontis star cluster. Two features of the disk around RECX 5 set it apart from other young, low-mass stars with protoplanetary disks: its mineralogy and its disk geometry. Band strengths of the crystalline silicate forsterite are a factor of two higher than that typically observed in T Tauri star disks, indicative of a high forsterite mass fraction. Continuum fluxes of the disk are inconsistent with either a flaring or flattened structure, suggesting a complex disk geometry. Radiative transfer modeling of the spectrum suggests that the disk has a gap at a radius of r = 0.6 AU, and that the disk density at r ≤ 33 AU is a factor of 100 lower than that of a continuous disk. A second disk gap might be centered at r = 24 AU. The RECX 5 disk has properties that are remarkably similar to the disk surrounding the Herbig Be star HD 100546, which is noted for having extreme mineralogy and geometry among Herbig star disks. Similar to a solution proposed for HD 100546, we speculate that the clearance of the RECX 5 disk at r ≤ 33 AU is a consequence of the formation of a Saturn-mass planet, with the planet being responsible for the striking difference in both the spectral energy distribution and chemical composition of the dust around RECX 5.