Have you ever wondered which places on Earth most resemble other planets? For some of us, imagining the landscape of other worlds might just be for fun, but scientists and engineers wonder about what the otherworldly places on Earth can tell us about neighbours like the Moon and Mars.
Working in the most unusual places on Earth can help us to prepare for human flights, robotic missions and the search for life beyond our own planet. These 'analogues' are chosen because they are similar in one way or another to particular planetary environments. They can be used for technical tests and research before the effort and expense of a launch into space.
The most hostile environments on Earth are home to unusual life forms. By studying these 'extremophiles' that can cope with extreme heat, cold, pressure or radiation on Earth, astrobiologists can consider whether certain environments in space might be home to similar tiny creatures. Needing unspoiled land, often without vegetation, means that astrobiologists and geologists often find themselves in very remote places.
Past research for ESA includes expeditions to Svalbard in conjunction with NASA. The teams visiting this remote island far to the north of Norway included geologists, biologists and engineers, and their tests included some of the instruments now working on Mars aboard the Curiosity rover.
Sites like the Atacama Desert, recently used to test a sampling rover for ESA's ExoMars mission, are valuable. Trials can find out what sort of terrain a rover can cross, what kind of slopes it can go up and down, and whether it can sample the surface.
The analogue sites are not all forbidding and inaccessible. Among the useful venues are impact craters in Arizona, USA, and the Rio Tinto river near Seville in Spain. A detailed catalogue of analogues on Earth for missions to the Moon and Mars was recently commissioned by ESA to help researchers.
"We examined what kind of interesting areas there are on Mars and the Moon, and how to find something similar on Earth," says Oliver Angerer, Human Exploration Science Coordinator for ESA.
"For example, if you want to study lava tubes on Mars, what is the nearest equivalent on Earth? Depending on your mission requirements, you can choose Iceland, Hawaii or Tenerife."
Sites listed in ESA's Catalogue of Planetary Analogues are scattered over all seven continents and include impact craters, lava flows, deserts and tundra.
The catalogue draws on the experience of a large network of planetary scientists and was compiled for ESA's General Studies Programme by researchers at the UK's Open University. It includes details of everything from the nearest petrol station to what kind of dangerous wildlife might be living nearby.
"I am particularly pleased with the amount of practical information included. The OU did a really excellent job on that side," says Oliver.
And what about a Mars or Moon analogue as a holiday destination?
"There are a lot of places in this catalogue that I would like to visit," says Oliver. "So far, I haven't been to the Dry Valleys in Antarctica, which is an amazing area for field activities. It's the closest you can get to being on another planet while staying on Earth."