Observing solar system objects with METIS

Abstract

Observations with the Mid-infrared ELT Imager and Spectrograph (METIS) at the upcoming Extremely Large Telescope (ELT) are expected to significantly enhance midinfrared astronomy, offering new insights into topics such as protoplanetary disks, galaxy physics, and solar system objects. Due to the ELT large aperture, the METIS instrument will include an adaptive optics (AO) system. This AO system relies only on natural guide stars, which imposes stringent constraints on the observability of fast-moving solar system targets. This thesis presents a study of the observation possibilities of solar-system objects with METIS, taking into account the constraints from its AO system. This work covers various aspects, from the development of a tool aiming at identifying suitable observation windows for solar system objects to the study of different targets. The constraints affecting observability—guide star brightness, angular separation, target motion, and observing conditions like Sun and target elevation—are first identified and implemented in the algorithm. The tool is then applied to various target types, revealing that fast-moving objects like Mercury, or comets close to their perihelion do not allow a guide star to remain close enough for a sufficiently long time to enable a proper observations. Similarly, Mars and main-belt asteroids offer only short windows, while slower targets like outer planets or trans-Neptunian objects allow longer observations, though low stellar density can still be a limiting factor, especially for the slowest objects. The impact of a more restrictive field of view and star brightness is also studied, showing that the most restrictive case of stars brighter than magnitude 12 often ensures an average of 10 windows per year, though it may require to put the target off-axis in the science camera, which would result in reduced operation capabilities. The study finally explores the potential of using asteroids and trans-Neptunian objects themselves as guide stars, expanding observing possibilities for otherwise challenging targets.