However, that has not stopped new entrants from continuing to join the fray, with novel twists on the basic scanning-probe design.

ECONOMIST: MONITOR

Nasa's efforts to locate MPL are continuing with cameras on board the orbiting probe Mars Global Surveyor scanning the planet's surface.

BBC: Mars probe canyon crash theory

Daniel Langleben, of the University of Pennsylvania, in Philadelphia, uses a brain-scanning technique called functional magnetic-resonance imaging to probe his subjects' honesty.

ECONOMIST: Lie detection