The Pseudo-zodi Problem for Edge-on Planetary Systems

TL;DR

The paper discusses how a dust cloud, invisible to mid-infrared surveys but visible at optical wavelengths, can mimic exozodiacal dust in edge-on planetary systems, complicating direct imaging of Earth-like exoplanets.

Contribution

It introduces the concept of the pseudo-zodiacal effect caused by inward-migrating dust, providing constraints on its properties and prevalence.

Findings

Pseudo-zodiacal dust can mimic exozodiacal dust brightness.

This effect could be present in about 50% of systems with cold debris belts.

Constraints on dust properties necessary for the effect are established.

Abstract

Future direct observations of extrasolar Earth-sized planets in the habitable zone could be hampered by a worrisome source of noise, starlight-reflecting exozodiacal dust. Mid-infrared surveys are currently underway to constrain the amount of exozodiacal dust in the habitable zones around nearby stars. However, at visible wavelengths another source of dust, invisible to these surveys, may dominate over exozodiacal dust. For systems observed near edge-on, a cloud of dust with face-on optical depth 10^-7 beyond ~5 AU can mimic the surface brightness of a cloud of exozodiacal dust with equal optical depth if the dust grains are sufficiently forward-scattering. We posit that dust migrating inward from cold debris belts via Poynting-Robertson drag could produce this "pseudo-zodiacal" effect, potentially making it ~50% as common as exozodiacal clouds. We place constraints on the disk radii and scattering phase function required to produce the effect.