Why doesn’t Rosetta need to be shielded against impacting dust grains from Comet 67P/Churyumov-Gerasimenko?
Close to the Sun, comets release large quantities of dust and gas to make the magnificent tails that stretch through space and can sometimes be seen from Earth. When ESA’s Giotto mission crossed the path of Comet Halley in 1986, it was travelling at 68 kilometres per second. At that speed it was ‘sandblasted’ by dust grains. The spacecraft was struck 12 000 times, each one eroded a little more of the spacecraft’s shielding until 7.6 seconds before closest approach, the spacecraft plunged into a particularly dense region. The collision of a ‘large’ one-gram particle sent it spinning, temporarily breaking contact with Earth. Rosetta will not experience this violence because, rather than making a headlong rush at Churyumov-Gerasimenko, it will fall gently into step with it. By keeping pace with the comet, the impact velocity of the dust grains is very much reduced and so Rosetta does not need the bulky shielding that Giotto required.
