NASA has issued the final commands to its New Horizons spacecraft ahead of the probe’s historic mission to explore a distant icy world four billion miles from Earth.
The probe could get to within 2,200 miles of the mysterious dwarf planet Ultima Thule before beaming images back to Nasa.
Ultima will become the most distant object ever explored by humanity when New Horizons shoots past it at around 5:33am GMT on New Year’s Day.
The dwarf planet sits at the very edge of the solar system, around one billion miles beyond Pluto in a region known as the Kuiper Belt.
In studying the 19-mile-wide object, scientists hope to get a better understanding of the ancient worlds that dominate the outer reaches of our star system.
Nasa has now confirmed it has sent its final commands to the probe ahead of Tuesday’s flyby.
The message included a two-second timing correction to ensures New Horizons point its cameras in the right place as it whizzes past its target.
“The spacecraft is healthy and we’re excited!” Mission Operations Manager Alice Bowman said.
New Horizons will snap thousands of photos as well as taking other scientific data in the hours leading up to and just beyond the flyby.
Scientists at Nasa are unsure what the New Horizons mission will uncover on Ultima.
Dr Alan Stern, the mission’s principal investigator, said: “What will Ultima reveal? No one knows. To me, that is what’s most exciting—this is pure exploration and fundamental science.”
Officially known as 2014 MU69, experts believe Ultima Thule is about 20 miles across, and has a red colour.
Scientists know it is a strange shape based on the unusual way it reflects sunlight, and some think the object may actually be a pair of space rocks.
Hal Weaver, a project scientist on the mission, said the icy world was “probably the most primitive object ever encountered by a spacecraft, the best possible relic of the early Solar System”.
Data collected by New Horizons will reveal what Ultima looks like, what it’s made of, how cold it is, and whether it has any moons.
The readings will also uncover whether Ultima has an atmosphere – one of the key components for life.
“In the space of one 72-hour period, Ultima will be transformed from a pinpoint of light — a dot in the distance — to a fully explored world,” Dr Stern said.
“It should be breathtaking.”
New Horizons, which is about the size of a baby grand piano, was launched in 2006 to explore Pluto’s surface.
After its successful flyby of the planet in 2015, mission planners won an extension from Nasa to prolong the probe’s journey.
They settled on an object deep inside the Kuiper Belt, the so-called “twilight zone” stretching beyond Neptune.