The rubber tracks (3) allow the Viking to travel over soft terrain such as desert, snow or mud because its load is evenly distributed over all four tracks, all of which are driven.

BBC: Factfile: Viking armoured vehicle

Skis were widely utilized in Central Asia and Europe, while snowshoes were common in the New World - probably because snow was more compact and less soft in the Old World, theorizes Huntford.

BBC: Where did skiing come from?

The experiment fell into deep snow in the far north of Sweden - and the possibility of a soft landing has the Strathclyde team hoping even more data can be recovered.

BBC: Sticking solar power station where the Sun shines

It takes seven or eight hours and strong legs to hike the whole crossing, past ice-blue crater lakes, over snow-covered ridges and through windswept mountain deserts, where totara trees cling to the soft black volcanic sand.

BBC: A return to Middle-earth