time calculations do not include unknown systematic uncertainties, which when added in quadrature to the estimated photon noise, will reduce the real-world S/N. We therefore do not consider our S/N$=10$ a conservative requirement.

Updates to Astrophysical Assumptions {#astrophysical_assumptions_section}
====================================

A number of astrophysical assumptions are required to estimate exoEarth candidate yield (see Table \[exoearth\_params\_table\]). These assumptions can have profound impacts on the yield and vary from study to study. Specifically, values used for the typical exoEarth candidate geometric albedo vary by 50% and the surface brightness of a Solar System-twin disk of exozodiacal dust varies by a factor of $2.5$ [e.g., @2010ApJ...715..122B; @2012PASP..124..418T]. In Appendices \[earth\_albedo\_appendix\]–\[exozodi\_appendix\] we examine these assumptions, along with the surface brightness of the local zodiacal cloud. Here we summarize those findings.

The typical albedo of an exoEarth candidate is unknown and may remain unknown prior to a direct imaging mission. For lack of observational constraints, previous works have commonly used Earth’s geometric albedo (though the value used has varied from $0.2$ to $0.3$). We found that a Lambert phase function with geometric albedo $A_G=0.2$ is a decent approximation of Earth’s reflectance, which is what we used in this work. A geometric albedo of $A_G=0.3$ overestimates the 