On 4 July, the US spacecraft Pathfinder, one of three launched last November, will enter the thin atmosphere of Mars. Though the Martian atmosphere is about 1 per cent of the Earth's, the buffeting will slow the spacecraft down from 7.5 kilometres a second to about 400 metres a second, or 900 miles an hour - which is slow enough for a parachute to open (rockets will help). Pathfinder will literally bounce into touch, bobbing on a cocoon of inflated airbags, before coming to rest on Martian soil. The touchdown will be in a region called the Ares Vallis, chosen because it seems to be a huge wadi or dried-up watercourse. A hatch will open, and out will pop a little wheeled robot rover called Sojourner, which will beetle about the immediate terrain, examining rock chemistry and reporting back to the lander, which will relay data and pictures back to Earth.

LRB 3 July 1997 | PDF Download