The Detectability of Exo-Earths and Super-Earths Via Resonant Signatures in Exozodiacal Clouds

TL;DR

This study models how Earth-like and super-Earth planets create resonant dust structures in exozodiacal clouds, revealing potential detectability of small planets through their dust signatures.

Contribution

It introduces a comprehensive simulation framework for resonant dust structures caused by exo-Earths and super-Earths, highlighting key parameters affecting observability.

Findings

Resonant structure contrast depends mainly on planet mass and a specific orbital parameter.

Largest dust grains dominate the optical depth in collisionless resonant rings.

Planets as small as a few times Mars's mass may be detectable at >10 AU.

Abstract

Directly imaging extrasolar terrestrial planets necessarily means contending with the astrophysical noise of exozodiacal dust and the resonant structures created by these planets in exozodiacal clouds. Using a custom tailored hybrid symplectic integrator we have constructed 120 models of resonant structures created by exo-Earths and super-Earths on circular orbits interacting with collisionless steady-state dust clouds around a Sun-like star. Our models include enough particles to overcome the limitations of previous simulations that were often dominated by a handful of long-lived particles, allowing us to quantitatively study the contrast of the resulting ring structures. We found that in the case of a planet on a circular orbit, for a given star and dust source distribution, the morphology and contrast of the resonant structures depend on only two parameters: planet mass and $\sqrt{a_{\rm p}}/\beta$, where $a_{\rm p}$ is the planet's semi-major axis and $\beta$ is the ratio of radiation pressure force to gravitational force on a grain. We constructed multiple-grain-size models of 25,000 particles each and showed that in a collisionless cloud, a Dohnanyi crushing law yields a resonant ring whose optical depth is dominated by the largest grains in the distribution, not the smallest. We used these models to estimate the mass of the lowest-mass planet that can be detected through observations of a resonant ring for a variety of assumptions about the dust cloud and the planet's orbit. Our simulations suggest that planets with mass as small as a few times Mar's mass may produce detectable signatures in debris disks for semi-major axes greater than 10 AU.