Rosetta fly-by at asteroid (21) Lutetia: An overview

On the journey to its target comet 67P/Churyumov-Gerasimenko the ESA Rosetta spacecraft had a close fly-by at the main-belt asteroid (21) Lutetia at a heliocentric distance of r=2.72 AU, and a geocentric distance of Δ=3.05 AU. Closest approach occurred on 10 July 2010, 15:45 UT at a distance of ∼3170 km. Rosetta passed the asteroid with a relative fly-by velocity of 15 km/s. The fly-by strategy allowed continuous observations of (21) Lutetia before, during and for 30 min after closest approach, and the spacecraft to go through zero phase angle 18 min before closest approach at a distance of 16400 km from the asteroid. Most of the scientific instruments on board Rosetta were switched on obtaining imaging and spectral observations covering wavelengths from the UV to sub-mm, as well as in-situ measurements of the asteroid and its direct environment. A brief summary of the fly-by is provided concentrating mainly on an overview of the instrument operations, the visual appearance of the asteroid during the encounter, and a synopsis of the fly-by results published in this special issue.