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Venus and Earth :

The four terrestrial planets, in true colors and to scale
Figure 1 : The four terrestrial planets, in true colours and to scale

The first two questions of the Cosmic Vision plan focus on the formation of planets and life, and on the solar system itself. Central to both of these goals is the study of the terrestrial planets. The three such planets in our Solar System – Earth, Mars, and Venus – show a wide range of evolutionary pathways, and so are key to understanding planets and their habitability everywhere, including in other stellar systems. Earth Observation research is well established, and Mars exploration, ongoing for nearly two decades, has its dedicated MREP funding line.

The NASA Magellan and ESA Venus Express missions to Venus have revealed a complex, dynamic planet with surprising similarities and differences from Earth, and yet it remains the least understood of these three planets. Further Venus exploration to find the causes of these differences is crucial to understanding how the Solar System works and the conditions for planet formation and the emergence of life.

It is of particular relevance in this era of discovery and characterisation of terrestrial planets in other stellar systems and their habitability.