  As we become aware of Earth's changing climate, and as we discover
terrestrial planets in other solar systems, we gain ever more reasons to study
the Earth's nearest neighbour and closest sibling, the only Earth-sized planet
besides our own that can be reached by our spacecraft. For the scientific and
programmatic reasons outlined in this document, Venus is a compelling target
for exploration. The science themes important for Venus research - comparative
planetology and planetary evolution - are common to all of planetary and
exoplanetary science. Many of the payloads required - radar and atmospheric
remote sensing, in situ mass spectrometers - are common to mission proposals
for many other solar system targets, as are mission technologies like high rate
deep-space telecommunications technologies. Venus-specific technology
developments meriting special attention include high-temperature systems and
balloons. Venus is an excellent proving ground for fundamental understanding of
geophysical processes of terrestrial planets; an excellent proving ground for
techniques of analysis of exoplanets; an indispensable part of our quest to
understand the evolution of Earthlike planets. For all these reasons, Venus
will be an ever more compelling theme in the coming decades, and we therefore
recommend its inclusion in the Voyage 2050 plan. We recommend that ESA aim to
have launched at least two M-class Venus missions by 2050, including the
EnVision M5 geophysics orbiter, and an in situ element such as a cloud-level
balloon; or an L-class mission combining these elements.
