Since the goal is to find Earth-like planets orbiting Sun-like stars, the Sun is an ideal proxy, as it is the only one astronomers can fully resolve. Dedicated instruments with high-precision spectrographs have been developed to observe the “Sun-as-a-star,” such as the High Accuracy Radial velocity Planet Searcher North (HARPS-N) solar telescope and the HARPS spectrograph (HELIOS). The main drawback is that only disc-integrated spectra are obtained, precluding a detailed analysis of individual stellar features.

According to the team, what is needed is a telescope that can offer three vital things: 1. Spatially resolved spectroscopy with very high wavelength stability 2. Very high spectral resolution to adequately resolve photospheric line asymmetries 3. Extended wavelength coverage, for the simultaneous observation of thousands of spectral lines probing different physical conditions.

This, they claim, can be achieved by linking the ESPRESSO spectrograph to a solar telescope — in this case, PoET. The solar telescope will observe the Sun at different spatial scales, corresponding to sunspots and solar granules, and send the light it gathers to ESPRESSO via optical fibers. The overall system involves three telescopes, starting with the main telescope (MT) developed by Officina Stellare. This telescope has a Gregorian configuration, standard for solar observations, and will observe small areas of the solar disc.