The three main science drivers of ESPRESSO as defined by ESO are:

• The search for rocky exo-planets: The high-precision radial velocity achievable with ESPRESSO (<10 cm/s in the HR and UHR modes) should allow the detection and characterization of Earth-mass planets in the habitable zone of GKM stars (the Earth imposes a velocity amplitude of 9 cm/s onto the Sun). ESPRESSO will thus fill the gap of rocky exo-planets with measured masses in the temperate region of solar-like stars. Coupled with the large collecting area of the VLT, ESPRESSO will be capable of determining the masses of planets around faint stars (e.g., most Kepler-validated planets) and follow-up the new candidates coming from new space missions like Gaia, TESS or PLATO. Also, ESPRESSO will play an important role in the characterization of exo-planet atmospheres.
• The possible variation of physical constants: The standard model of particle physics depends on many (≈ 27) independent numerical parameters that determine the strengths of the different forces and the relative masses of all known fundamental particles. Two of these parameters are the fine-structure constant (α) and the proton-to-electron mass ratio (µ). Their constancy has been demonstrated on timescales of a few years. Astronomy, however, gives the opportunity to test this constancy in Gyr timescales by observing the spectra of distant quasars. Only a high-resolution spectrograph that combines a large collecting area with extreme wavelength precision can perform these tests precisely. A relative variation in α or μ of 1 ppm leads to velocity shifts of about 20 m/s between typical combinations of transitions. ESPRESSO is expected to provide an increase in the accuracy of the measurement of these two constants by at least an order of magnitude compared to VLT/UVES.
• The chemical composition of stars in nearby galaxies: To understand galaxy formation, we need to know the chemical composition of local galaxies. ESPRESSO will give the chance to have a first but important glimpse into this, although extremely large telescopes will be needed for a definitive answer.

Apart from these main scientific questions, ESPRESSO will be an outstanding tool to explore many areas of astronomical research such as asteroseismology, the study of metal-poor stars, the expansion of the Universe, galactic winds, etc. A summary of these can be found in Pepe et al. (2014).

Science Verification papers

The Science Verification phase of ESPRESSO (in 4-UT mode only) is foreseen to take place in February 2019 and the corresponding call for proposals will be advertised in due time. In this section, we will summarize the outcome of this phase.

Selected Science Results

ESPRESSO can be used for a variety of science. A handful of published science cases will be outlined here.

Published Papers involving ESPRESSO

• Through telbib (ESO Library)
• Papers with the mention of ESPRESSO in their abstract from ADS