In order to achieve the Science Objectives a space-based mission is required, avoiding the perturbing effects (turbulence and thermal emission) of the Earth's atmosphere. As detecting the thermal emission of exoplanets requires observations at micrometer wavelengths (the thermal emission of Earth peaks around 10 micrometer), the current project baseline foresees a nulling interferometer concept consisting of several formation flying collector telescopes with a beam combiner spacecraft at their center. The measurement principle is both simple and elegant: the instrument acts as a spectrograph from which the stellar flux is removed by destructive interference, while the signal from any orbiting planet is transmitted to the output of the instrument. This allows the nulling interferometer to observe non-transiting exoplanets and build up signal-to-noise quickly without having to launch a very large, single aperture telescope. The extremely good inner working angle, i.e., the high spatial resolution required to separate the exoplanets' signal from that of the host star on the detector, is provided by the separation between the collector telescope, which, in principle, can be adjusted depending on the science requirements. In addition to the nulling mode, LIFE could also be operated in constructive imaging mode for other science cases.
LIFE is based on the heritage of older mission concepts such as ESA's Darwin or NASA's TPF-I . In contrast to the mid 2000s when those concepts were studied, we today have a much more comprehensive understanding of the existing exoplanet population, allowing a much more robust quantification of science objectives, science requirements and expected science yield.
In spring 2020 we kicked off NICE - the Nulling Interferometric Cryogenic Experiment for LIFE. The goal of NICE is to build a nulling testbed to promote LIFE and to enhance the technology readiness level of broadband nulling interferometry for LIFE and ground based nullers. The long term goal of NICE is to demonstrate the required nulling performance in terms of starlight suppression and stability under cryogenic conditions and with flux levels similar to those from real astrophysical sources. Details about NICE can be found here.
In addition, most technologies required to fly a space-based nulling interferometer have now reached a Technology Readiness Level (TRL) of 5, which means that the components have been tested and validated in their relevant environment. In particular, key technologies that were considered immature in 2007, when most ESA/Darwin and NASA/TPF-I activities came to a hold, have now been demonstrated on test-benches (e.g., deep nulling) or in space (e.g., formation flying). More information is provided here or here.
A comprehensive assessment of all major technologies is currently underway, which will serve as basis for the development of a technology development roadmap.