Large Interferometer For Exoplanets (LIFE) IV. Ideal kernel-nulling array architectures for a space-based mid-infrared nulling interferometer

Aims. Optical interferometry from space for the purpose of detecting and characterising exoplanets is seeing a revival, specifically from missions such as the proposed Large Interferometer For Exoplanets (LIFE). A default assumption since the design studies of Darwin and TPF-I has been that the Emma X-array configuration is the optimal architecture for this goal. Here, we examine whether new advances in the field of nulling interferometry, such as the concept of kernel-nulling, challenge this assumption. Methods. We develop a tool designed to derive the photon-limited signal-to-noise ratio of a large sample of simulated planets for different architecture configurations and beam combination schemes. We simulate four basic configurations: the double Bracewell/X-array, and three kernel-nullers with three, four, and five telescopes respectively. Results. We find that a configuration of five telescopes in a pentagonal shape, using a five-aperture kernel-nulling scheme, outperforms the X-array design in both search (finding more planets) and characterisation (obtaining better signal, faster) when the total collecting area is conserved. This is especially the case when trying to detect Earth twins (temperate, rocky planets in the habitable zone), showing a 23% yield increase over the X-array. On average, we find that a five-telescope design receives 1.2 times more signal than the X-array design. Conclusions. With the results of this simulation, we conclude that the Emma X-array configuration may not be the best choice of architecture for the upcoming LIFE mission, and that a five-telescope design utilising kernel-nulling concepts will likely provide better scientific return for the same collecting area, provided that technical solutions for the required achromatic phase shifts can be implemented.