German Aerospace Center's (DLR) 'Mole' device has started digging the surface of Mars and has reached an estimated depth of around 35 centimetres, NASA revealed. 'Mole' landed around 4,000 hammer blows over a period of four hours in its first sequence. Sent to Mars aboard NASA's InSight lander, 'Mole' will deploy 14 temperature sensors to measure Mars' internal temperature distribution.