  One of the most exciting scientific challenges is to detect Earth-like
planets in the habitable zones of other stars in the galaxy and search for
evidence of life.
  The ability to observe and characterise dozens of potentially Earth-like
planets now lies within the realm of possibility due to rapid advances in key
space and imaging technologies. The associated challenge of directly imaging
very faint planets in orbit around nearby very bright stars is now well
understood, with the key instrumentation also being perfected and developed.
Such advances will allow us to develop large transformative telescopes,
covering a broad UV-optical-IR spectral range, which can carry out the detailed
research programmes designed to answer the questions we wish to answer:
  Carry out high contrast imaging surveys of nearby stars to search for planets
within their habitable zones. Characterise the planets detected to determine
masses and radii from photometric measurements. Through spectroscopic studies
of their atmospheres and surfaces, search for habitability indicators and for
signs of an environment that has been modified by the presence of life.
  Active studies of potential missions have been underway for a number of
years. The latest of these is the Large UV Optical IR space telescope (LUVOIR),
one of four flagship mission studies commissioned by NASA in support of the
2020 US Decadal Survey. LUVOIR, if selected, will be of interest to a wide
scientific community and will be the only telescope capable of searching for
and characterizing a sufficient number of exoEarths to provide a meaningful
answer to the question - Are we alone?.
  This paper is a submission to the European Space Agency Voyage 2050 call for
white papers outlining the case for an ESA contribution to a Large UVOIR
telescope.
