A Nasa probe is to start photographing the icy world of Pluto, to prepare itself for a historic encounter in July.
The New Horizons spacecraft has travelled 5bn km (3bn miles) over nine years to get near the dwarf planet.
And with 200m km still to go, its images of Pluto will show only a speck of light against the stars.
But the data will be critical in helping to align the probe properly for what will be just a fleeting fly-by.
Pluto will be photographed repeatedly during the approach, to determine the probe’s position relative to the dwarf planet, explained Mark Holdridge, from the Johns Hopkins University’s Applied Physics Laboratory (JHUAPL) in Baltimore.
“We then perform a number of correction manoeuvres to realign our trajectory with the reference trajectory, thus ensuring we hit our aim point to travel through the Pluto system,” he said.
Any initial correction is likely to be made in March.
When New Horizons arrives at Pluto it will be moving so fast – at almost 14km/s – that going into orbit around the distant world is impossible; it must barrel straight through instead.
One complication is that the seven different instruments aboard the spacecraft need to work at different distances to get their data, and so the team has constructed a very elaborate observation schedule for them all.
But what this means is that very precise timing will be required to make sure the flyby runs smoothly.
The closest approach to Pluto is set for around 11:50 GMT on 14 July – at a miss distance of roughly 13,695km from the surface.
Mission planners want the exact timings nailed to within 100 seconds. New Horizons will know then where and when to point the instruments.