Necroplanetology: Simulating the Tidal Disruption of Differentiated Planetary Material Orbiting WD 1145+017

Abstract

The WD 1145+017 system shows irregular transit features that are consistent with the tidal disruption of differentiated asteroids with bulk densities < 4 g cm −3 and bulk masses 10 21 kg (Veras et al. 2017).We use the open-source N-body code REBOUND (Rein & Liu 2012) to simulate this disruption with different internal structures: varying the core volume fraction, mantle/core density ratio, and the presence/absence of a thin low-density crust. We allow the rubble pile to partially disrupt and capture lightcurves at a specific point during the disruption at cadences comparable to those from ground-based photometry. As a proof-of-concept we show that varying these structural parameters have observationally distinguishable effects on the transit light curve as the asteroid is disrupted and compare the simulation-generated lightcurves to data from Gary et al. (2017). With the caveat that our simulations do not model the sublimation in detail or account for its effects on orbital evolution, we find that a low core fraction and low mantle/core density ratio asteroid is most consistent with the stable transit feature present for multiple weeks circa April 2016 (referred to as G6121 in Gary et al. (2017) and A1 in Hallakoun et al. (2017)). Connecting tidal disruption simulations to photometry suggests characteristics for the interior structure and composition of an exoplanetary body, information that is only possible because we are observing the death of the planetary system in action. All-sky survey missions such as TESS and LSST will be able to detect other systems like WD 1145+017, creating a sample of subjects for a new subfield of planetary science: necroplanetology.

Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments

“…This calculation safely ignores the spin of the asteroid (see Appendix A). While the fragments initially form in a cluster, with core and mantle regions not necessarily disrupting simultaneously (Veras et al 2017;Duvvuri et al 2020;Malamud & Perets 2020a), they shear out over time, and completely fill a tidal disc after a well-defined timescale (see Appendix B for a derivation of this filling time). The width of the tidal disc that forms in this manner depends chiefly on the size of the asteroid and on its semi-major axis.…”

Planetary Systems Around White Dwarfs

“…Substantial theoretical work on this system (Rappaport et al 2016;Farihi, von Hippel & Pringle 2017b;Gurri, Veras & Gänsicke 2017;Veras et al 2017a;Xu et al 2019a;Duvvuri, Redfield & Veras 2020;O'Connor & Lai 2020) has placed constraints on the progenitor minor planet mass (about 10% of Ceres' mass), bulk density (Vesta-like), interior structure (probably differentiated), placement relative to the circumstellar dust and gas in the system, and dynamical history through tidal shrinkage and circularization and ram pressure drag. Because the minor planet effluences orbit WD 1145+017 at a near-constant separation of 0.005 au, which corresponds to the rubble-pile disruption (Roche) limit, the disruption in that system is assumed to be tidal.…”

The lifetimes of planetary debris discs around white dwarfs

“…The highest possible mass of the progenitor of the planetesimals orbiting WD 1145+017 is thought to be about 10 per cent the mass of Ceres, such that Mp 10 20 kg (Rappaport et al 2016;Veras et al 2017a;Gurri et al 2017). The density of this progenitor, however, is not necessarily uniform (Duvvuri et al 2020), leaving ρp unconstrained. Indeed, a disc composed of solely iron-rich core fragments is not unreasonable (Manser et al 2019), just as is a disc composed of only porous rubble piles.…”