As of 2021 about 5000 planets have been found to orbit stars other than the Sun. The vast majority of these exoplanets have been found with indirect techniques that detect the wobble of the parent star or a change in the star’s intensity when a planet passes in front of it. These known exoplanets are typically much closer to the host star and also much heavier than the planets in our own solar system. Based on the large statistics of exoplanetary systems now available, we know that up to half of all solar-like stars in the sky have Earth-mass planets. And some of these planets will be located in the habitable zone, a range of distances from a star where liquid water may exist on a planetary surface.
To detect solar-system like planetary systems, we need to directly image the area very close to the host star. Current telescopes allow us to directly image planets that are far away from their host star and only a few million years old so that they still ‘glow’ from the formation process. To directly image old and small planets in reflected starlight, we need a much larger telescope such as the Extremely Large Telescope (ELT) currently under construction. An ELT instrument that is built by LEOPARD scientists for the particular purpose of directly imaging planets in reflected starlight is EPICS.
Once we can directly image planets in reflected starlight, we can characterize their atmospheres and surfaces with techniques that are also used for remote observations of planets and even the Earth: spectroscopy and polarimetry from visible light to the near- infrared.
An instrument like EPICS will allow us to determine the chemical composition of their atmosphere, the abundance of different gases including oxygen and water vapor, the presence of clouds, liquid water and potentially even the presence of vegetation. Observations over extended periods will allow us to determine changes in the atmosphere and surfaces due to rotation and weather.
