  Since the first discovery of a planet outside of our Solar System in 1995,
exoplanet research has shifted from detecting to characterizing worlds around
other stars. The TESS (NASA, launched 2019) and PLATO mission (ESA, planned
launch 2026) will find and constrain the size of thousands of exoplanets around
bright stars all over the sky. Radial velocity measurements are needed to
characterize the orbit and mass, and complete the picture of densities and
composition of the exoplanet systems found. The Ariel mission (ESA, planned
launch 2028) will characterize exoplanet atmospheres with infrared
spectroscopy. Characterization of stellar activity using optical spectroscopy
from the ground is key to retrieve the spectral footprint of the planetary
atmosphere in Ariel's spectra. To enable the scientific harvest of the TESS,
PLATO and Ariel space missions, we plan to install MARVEL as an extension of
the existing Mercator Telescope at the Roque De Los Muchachos Observatory on La
Palma (SPAIN). MARVEL consists of an array of four 80 cm telescopes linked
through optical fibers to a single high-resolution echelle spectrograph,
optimized for extreme-precision radial velocity measurements. It can observe
the radial velocities of four different stars simultaneously or, alternatively,
combine the flux from four telescopes pointing to a single faint target in one
spectrum. MARVEL is constructed by a KU Leuven (Belgium) led collaboration,
with contributions from the UK, Austria, Australia, Sweden, Denmark and Spain.
In this paper, we present the MARVEL instrument with special focus on the
optical design and expected performance of the spectrograph, and report on the
status of the project.
