And yet, questions remain about what these worlds are like and whether they could host life.
Ariel, however, will not answer the latter question as it will focus its attention on worlds that appear least likely to host life as we know it on Earth.
Some of these worlds, for example, reach temperatures of more than 2,000C, and yet, these hellish conditions will reveal to Ariel many of the molecules swirling in their atmospheres.
The Ariel Consortium Project Manager, Paul Eccleston, of STFC RAL Space, said: “This represents the culmination of lots of preparatory work by our teams across the world over the last five years in order to demonstrate the feasibility and readiness of the payload.
“We now go full speed ahead to fully develop the design and start building prototypes of the instrumentation on the spacecraft.”