  Exoplanet science is booming. In 20 years our knowledge has expanded
considerably, from the first discovery of a Hot Jupiter, to the detection of a
large population of Neptunes and super-Earths, to the first steps toward the
characterization of exoplanet atmospheres. Between today and 2025, the field
will evolve at an even faster pace with the advent of several space-based
transit search missions, ground-based spectrographs, high-contrast imaging
facilities, and the James Webb Space Telescope. Especially the ESA M-class
PLATO mission will be a game changer in the field. From 2024 onwards, PLATO
will find transiting terrestrial planets orbiting within the habitable zones of
nearby, bright stars. These objects will require the power of Extremely Large
Telescopes (ELTs) to be characterized further. The technique of ground-based
high-resolution spectroscopy is establishing itself as a crucial pathway to
measure chemical composition, atmospheric structure and atmospheric circulation
in transiting exoplanets. A high-resolution spectrograph covering the visible
and near-IR domains, mounted on the European ELT, will be able to detect
molecules such as water vapour, carbon dioxide and oxygen in the atmospheres of
habitable planets under favourable circumstances. E-ELT HiRES is the perfect
ground-based match to the PLATO space mission and represents a unique
opportunity for Europe to lead the world into the era of exploration of
exoplanets with habitable conditions. HiRES will also be extremely
complementary to other E-ELT planned instruments specialising in different
kinds of planets, such as METIS and EPICS.
