Just last night, I found an interesting question in my inbox, "Out of interest, what is the closest that Rosetta gets to Planck during the fly-by?"
It was from Stuart Lowe, member of the Planck Low Frequency Instrument team at Jodrell Bank Observatory in the UK.
We asked Trevor Morley, one of the Flight Dynamics specialists at ESOC working on Rosetta, if he could help. He sent these minimum separation distances from Rosetta:
Planck : 1.225 million km at 03:39 CET on 12 November.
Herschel: 1.456 million km at 07:53 CET on 12 November
That's quite a distance, but tiny compared to what Rosetta's already covered since the start of her mission. By the time the swingby has been completed, this figure will be almost 4500 million km!--Amruta