Even though we like to complain about our weather, we live on a planet that almost seems to have been created specifically for humans (rather than humans having evolved to suit the conditions). Temperatures are generally moderate, and the worst effects of cosmic rays and radiation from the sun are mitigated by our atmosphere. Scientists call planets that enjoy this fortunate combination of conditions Goldilocks planets – not too hot and not too cold, but just right, as in the story of Goldilocks and the Three Bears, where Goldilocks tests three bowls of porridge until she finds the one that is just right. Goldilocks is just one of the new meanings added to the Cambridge dictionary that are connected with space exploration and colonization.
What if conditions were to change to make life on earth impossible? We find another one, of course. Planets in our own solar system don’t fit the bill. Unmanned spacecraft, such as the Pioneer and Voyager space probes and the Galileo orbiter, have shown us, for example, that the Martian atmosphere is too thin to protect us, and the planets of the outer solar system, Jupiter, Uranus, and Neptune, as well as having toxic atmospheres, are far too cold to support human life.
(Incidentally, previous editions of the Cambridge dictionary described Pluto as the ninth planet. It has now been demoted, no longer significant enough to be called a planet, and is now classified as a dwarf planet, like hundreds of others, and has the more impersonal designation 134340.)
We need to look beyond our solar system to find terrestrial planets (also known as earth-like planets) that might be more suitable for human habitation. Some of these exoplanets, or extrasolar planets (planets that orbit stars other than our sun), may yet prove to be habitable. The question is: how do we get there? Spacefarer Tim Peake, the latest British astronaut to visit the International Space Station, is helping to pave the way. Perhaps we will soon all be able to become space tourists, zipping between the planets in spaceplanes. The countdown has begun!