The Curry's and PC World owner is due to unveil sales data from the Christmas period, when rival Comet collapsed.

BBC: French Connection and Thorntons down on trading reports

Deep Impact has now set its sights on comet Ison during a 36-hour period in mid-January.

BBC: Comet Ison caught on film by Deep Impact craft

That would give it an orbital period of 341 years the longest yet measured and far longer than, for example, comet Halley, which goes around the sun in a sprightly 76 years.

ECONOMIST: Comet Ikeya-Zhang is enlivening the skies