Dust formation in the outflows of catastrophically evaporating planets

Abstract

Ultra-short period planets offer a window into the poorly understood interior composition of exoplanets through material evaporated from their rocky interiors. Among these objects are a class of disintegrating planets, observed when their dusty tails transit in front of their host stars. These dusty tails are thought to originate from dust condensation in thermally-driven winds emanating from the sublimating surfaces of these planets. Existing models of these winds have been unable to explain their highly variable nature and have not explicitly modelled how dust forms in the wind. Here we present new radiation-hydrodynamic simulations of the winds from these planets, including a minimal model for the formation and destruction of dust, assuming that nucleation can readily take place. We find that dust forms readily in the winds, a consequence of large dust grains obtaining lower temperatures than the planet’s surface. As hypothesised previously, we find that the coupling of the planet’s surface temperature to the outflow properties via the dust’s opacity can drive time-variable flows when dust condensation is sufficiently fast. In agreement with previous work, our models suggest that these dusty tails are a signature of catastrophically evaporating planets that are close to the end of their lives. Finally, we discuss the implications of our results for the dust’s composition. More detailed hydrodynamic models that self-consistently compute the nucleation and composition of the dust and gas are warranted in order to use these models to study the planet’s interior composition.

DMPP-3: confirmation of short-period S-type planet(s) in a compact eccentric binary star system, and warnings about long-period RV planet detections

“…For the first time, they include models for the formation of the dust grains, as well as progressing the treatment of dust heating by considering both stellar and re-emitted thermal radiation from the planet itself. Their analysis builds on previous work, and predicts mass-loss rate for a range of planet masses and temperatures (Figure 6; Booth et al 2022). This then implies how long the planets would survive under gas and dust loss.…”

“…Perez-Becker & Chiang (2013) found for 𝑇 = 2145𝐾, rocky planets of initial mass above ∼ 0.12 M ⊕ are able to survive for longer than 10 Gyr (see their figure 9). Booth et al (2022) extend the simulations of CDE mass-loss history. For the first time, they include models for the formation of the dust grains, as well as progressing the treatment of dust heating by considering both stellar and re-emitted thermal radiation from the planet itself.…”

“…Fig. 6 in Booth et al 2022). The mass-loss would be negligible in comparison to the total mass of the planet, and the age of the system.…”

aiolos – A multipurpose 1D hydrodynamics code for planetary atmospheres

“…AIOLOS is already being applied to a range of problems. Booth et al ( 2023 ) used AIOLOS to model dust formation in the winds of ultrashort period planets.…”

“…those with temperature inversions and those for which reradiation is important (e.g. Booth, Owen & Schulik 2023 ) In the numerical context, traditional codes lack some important aspects which are desired to solve a hydrodynamic multispecies problem with bolometric and high-energy radiation transport, hence we now briefly outline our technical reasoning for presenting a new simulation code.…”