Searching for exoplanets with HEPS: I. detection probability of Earth-like planets in multiple systems

Abstract

The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to compute accurate planet parameters from observation data and reduce detectability. The degeneracy problem is extremely critical, especially in a space mission which has limited observation time and cadence. In this series of papers, we study the detectability of habitable Earth-mass planets in different types of multi-planet systems, aiming to find the most favorable targets for the potential space mission–Habitable ExoPlanet Survey (HEPS). In the first paper, we present an algorithm to find planets in the habitable zone around solar-like stars using astrometry. We find the detectability can be well described by planets’ signal-to-noise ratio (SNR) and a defined parameter S = M2/(T1 – T2)2, where M2 and T2 are the mass and period of the second planet, respectively. T1 is the period of the planet in the habitable zone. The parameter S represents the influence of planetary architectures. We fit the detectability as a function of both the SNR of the planet in the habitable zone and the parameter S. An Earth-like planet in a habitable zone is harder to detect (with detectability PHP < 80%) in a system with a hot Jupiter or warm Jupiter (within 2 AU), in which the parameter S is large. These results can be used in target selections and to determine the priority of target stars for HEPS, especially when we select and rank nearby planet hosts with a single planet.