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.
While current science yield estimates of LIFE (such as presented here and here) are based on the original ESA/Darwin "Emma X-array" concept, it is planned to re-assess and trade different possible spacecraft configurations in the near future including, for instance, number and size of the collector telescopes.
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.