LIFEsim: Methods for predicting the exoplanet yield of the future LIFE mission

The Large Interferometer For Exoplanets (LIFE) initiative is proposing a space-based mid-infrared nulling interferometer to directly image a large number of terrestrial exoplanets in the habitable zone around nearby stars. To ensure that the mission can answer its set of scientific goals concerning the atmospheres and habitability of those planets, it is vital to predict the number and distribution of exoplanets that are detectable with LIFE. Additionally, first estimates for technical requirements are needed to prove feasibility of such a mission.

In this contribution, we present the pipeline as well as technical and physical assumptions used in the mission simulation tool LIFEsim. In the mid-infrared, LIFE will discover many planets in a radius and insolation parameter space which is inaccessible by current instruments. To correctly predict the absolute number of detectable planets, we therefore populate nearby main-sequence stars with synthetically generated planets based on statistic from the Kepler mission.

These planets are fed into an instrument simulator for a chopping dual-Bracewell nulling interferometer, where symmetry properties of the beam combination and the target systems are used to discern the planet signal from background noise sources. For these background sources, we model the most relevant contributions from the host star as well as the thermal emission of the exo-zodiacal and the local-zodiacal dust. Under the assumption of the measurement being impacted only by these fundamental noise sources, the planets are assigned a photon-noise based signal-to-noise ratio which is used to determine their detectability.

The LIFE mission will spend 2.5 years of its operation to search for previously undetected exoplanets. We present observing sequences that distribute this available observation time onto the available targets while optimizing for either a total maximum number of detected planets or a maximum number of planets detected in the habitable zone.

We report that LIFEsim is capable of predicting the exoplanet detection yield of the LIFE mission under the assumptions laid out above. We present that LIFE is able to detect roughly 550 exoplanets within the 2.5 years search phase, many of which can be categorized as warm super-earths. We additionally show that the exoplanet yield is a strong function of instrumental parameters like the primary mirror size.