We propose a conceptual design study for a 12-metre wide-field spectroscopic survey telescope (WST) with simultaneous operation of a large field-of-view (3 sq. degree), high-multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 arcmin integral field spectrograph (IFS). In scientific capability these specifications place WST far ahead of existing and planned facilities. In only 5 years of operation, the MOS would target 250 million galaxies and 25 million stars at low spectral resolution plus 2 million stars at high resolution. Without need for pre-imaged targets, the IFS would deliver 4 billion spectra offering many serendipitous discoveries. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work in synergy with future ground and space-based facilities. We show how it can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; the origin of stars and planets; and time domain and multi-messenger astrophysics. WST’s uniquely rich dataset may yield unforeseen discoveries in many of these areas. The study will deliver telescope and instrument designs, cost estimates, an updated science white paper and survey plan, concept studies for data management, and a facility operation concept. The telescope and instruments will be designed as an integrated system and will mostly use existing technology, with the aim to minimise the carbon footprint and environmental impact. We will propose WST as the next ESO project after completion of the 39-metre ELT. Our consortium includes institutes from Australia, which has a strategic partnership with ESO and aims to apply shortly for full membership. Together with ESO and institutes in 9 European countries, our team has the necessary technical and scientific expertise, and brings 70 years of in-kind effort to the proposed study.

FIERCE aims at providing the long-needed step forward to tackle the challenges of stellar activity on the search for Exoearths. The detection and characterisation of other Earths, planets with the physical conditions to hold liquid water and thus potential life-sustaining environments, is a bold objective of present day astrophysics. This goal continuously pushes the development of new ground- and space-based instrumentation. However, the quest for other Earths is severely limited by astrophysical ``noise'' from the host stars, whose signatures distort the spectra that are used to detect and characterise them. Existing methods usually circumvent the problem without a detailed understanding of the individual sources of variability. This is insufficient to reach the required precision levels. To enable the full scientific success of major exoplanet research facilities a new approach is clearly needed. With FIERCE, the PI will employ his competitive team, together with the strong participation in cutting-edge ESO and ESA projects and missions, to break through in this obstacle. The ultimate goal is to i) develop novel approaches to identify, model, and correct stellar spurious signals in radial velocity measurements down to 10 cm/s, and ii) obtain a comprehensive understanding of the impact of stellar granulation and activity on the detection of exoplanet atmospheres. To this end, FIERCE will approach the problem of stellar ``noise'' from a whole new angle, building a dedicated facility, the Paranal solar Espresso Telescope (PoET). PoET will connect to the recently commissioned ESPRESSO spectrograph and, using the Sun as a proxy, allow to unambiguously identify and understand the sources of relevant variability in solar-type stars. Ambitious, timely, and feasible, this project will provide crucial information for the success of present and future major efforts aiming at detecting and characterising other Earths.