NASA named the rover which forms part of the Mars Pathfinder mission Sojourner following a year-long worldwide competition; the winner was Valerie Ambroise of Bridgeport, Connecticut, who suggested it be named after Sojourner Truth, a nineteenth-century black feminist and campaigner for the abolition of slavery, who invented the name to replace her slave name Isabella Van Wagener when she was freed.
Sojourner is hardly a common word these days, to the extent that one British newspaper mistakenly remarked just after the lander arrived on Mars on 4 July 1997 that NASA had found it particularly appropriate because it means “traveller”, an unfortunate error copied from the original press release of the Jet Propulsion Laboratory two years earlier that announced the rover’s name.
Its principal sense in English is “(a person or thing) which stays in some place only for a short time”; though this necessarily implies moving from place to place, it is the stay which is emphasised, not the travelling. In origin, it means “to spend the day (somewhere)”: it derives from the Latin subdiunare, with that meaning, whose root is diurnum, “day”, from which we get diurnal (and also journey, which originally meant the distance one could travel in one day).
The other core meaning of sojourn in English is temporariness. The Bible employs this sense, in I Chronicles, when it says “For we are strangers before thee, and sojourners, as were all our fathers: our days on the earth are a shadow, and there is none abiding”. (It was this biblical association that caused Sojourner Truth to adopt it as her first name.)
As a working unit Sojourner may indeed be a temporary resident of Mars, but the one thing we are pretty sure of is that in the long term the Mars rover will be staying more or less where it is, either until the dust storms of the thin Martian atmosphere wear it to nothing, or some future curator collects it and puts it in the Museum of Mars.