The European Space Agency (ESA) has held an hour-long hangout to explain what's likely to happen when its Rosetta spacecraft touches down on Comet 67p.

On Sunday, after a final manoeuvre, the spacecraft will start a 14-hour descent.

Operations manager Sylvain Lodiot says the agency expects Rosetta to land somewhere inside a 600 x 400 metre footprint target zone, to be refined on September 30 (European time) as it descends. The mission plan calls for touchdown at 10:40PM UTC (11:40PM in the UK) but that pesky speed of light problem means we won't know what's happened for about 40 minutes.

While the descent will be gentle – below one metre/second – Rosetta wasn't designed for a landing, so it will certainly bounce and tumble after its first touchdown, and Lodiot expects damage to the solar panels or instruments.

Before that, flight director Andrea Accomazzo said, the world will get a very close look at the comet, and the descent should provide insights into its internal structure beyond those already gleaned by the Philae lander.

Rosetta is now around 4.1 km from the centre of the comet, or about 2.1 km from its surface, having made a slightly closer approach and then received a “kick” from the comet from subsequent orbits.

Claire Vallat of ESA/ESAC (the European Space Astronomy Centre) told the hangout most of Rosetta's instruments will remain in service right up to the end: the GAIDA dust instruments and VIRTIS spectrometer will be out of action.

However, she said, “it's an extraordinary opportunity” to get another close-up view of the comet: the region where dust and gas mix, the morphology of the surface, the solar wind's interaction with the comet are all on the science list.

Hi @ESA_Rosetta! Comet #67P on 20 Sep 16 from a distance of 14km (more at https://t.co/iyNItSmDr7) pic.twitter.com/eEEXKTHK2y — Rosetta OSIRIS (@Rosetta_OSIRIS) September 20, 2016

“We'll be able to study the surface with unprecedented resolution” Vallat said. “We are trying to get as complete picture as possible”.

While there's a sentimental affection for Rosetta, it's already near its end of life: as it gets further away from the Sun, its propellant will freeze, making any further manoeuvres impossible; and it's already suffering shortages of power. ®

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