It's on. The scientists are in place. NASA has confirmed it is ready.
An artist's illustration of NASA's New Horizons spacecraft as it flies by Ultima Thule (2014 MU69) in the Kuiper Belt beyond Pluto on Jan. 1, 2019. Photo: NASA/JHUAPL/SwRI
The most distant flyby by a space probe is set to happen, starting tomorrow, New Year's Eve. The New Horizons satellite, which gave us the first close-up glimpse of Pluto three years ago, is to fly past the furthest object man has reached. Nicknamed 'Ultima Thule', Latin for a mythical place beyond the limits of the known world, it is an object of rock and ice and is thought to date to the very earliest times of the solar system.
NASA lead investigator Alan Stern blogged that New Horizons will swoop three times closer to Ultima Thule than it did when it flew past Pluto.
He wrote: "On Saturday, Dec. 15, the New Horizons hazard watch team concluded its work, having found no moons or rings in the path of New Horizons on its planned closest approach to Ultima. With that information and a unanimous finding by our mission stakeholders team, I informed NASA that we are "go" to fly by Ultima on the trajectory that yields the best science. As a result, New Horizons will approach to within 3,500 kilometres (about 2,200 miles) of Ultima early on New Year's Day. There is no longer any chance we will divert to a farther flyby distance with consequently lower-resolution images."
He said that the exploration of Ultima Thule is fascinating because no-one is quite sure what New Horizons will find.
"What will Ultima reveal? No one knows. To me, that is what's most exciting-this is pure exploration and fundamental science!"
What scientists do hope is that Ultima Thule may give some clues as to what the early stages of planet formation look like.
Here is a guide from the BBC to what the next few days could be like:
How do I follow New Horizons?
Good question. The best way is to follow NASA's trajectory page for New Horizons. It counts down where the New Horizons is and when it is projected to encounter Ultima Thule.
There are also various twitter accounts counting down to the encounter.
Investigator Alan Stern is here.
His countdown feed is here.
What do we know about Ultima Thule?
Very little. The object was only discovered four years ago by the Hubble telescope in a search for potential targets that New Horizons could reach after its Pluto encounter.
Initially catalogued as (486958) 2014 MU69, it was given the more catchy nickname of Ultima Thule (Pronounced: Too-lee) after a public consultation exercise.
Like many Kuiper belt objects of its type, it is likely to be composed of dust and ices that came together at the dawn of the Solar System more than 4.5 billion years ago.
Theory suggests such bodies will take on an elongated or lobate form. Think potato or peanut.
Its surface should be very dark, having being "burnt" through the eons by high-energy radiation - cosmic rays and X-rays.
New Horizons will study Ultima's shape, composition and environment.
Scientists hope Ultima can provide insights on how these distant objects formed. One idea is that they grew from the mass accretion of a great many pebble-sized grains.
What can we expect from the flyby?
Don't blink, you might miss it. Unlike the encounter with Pluto in July 2015, there won't be increasingly resolved images on approach to admire. Ultima will remain a blob in the viewfinder pretty much until the day of flyby, which has 05:33 GMT (6.30pm NZDT) set as the time of closest approach.
However, the much reduced separation between the probe and Ultima (3,500km versus 12,500km at the dwarf planet) means that finer detail in the surface will eventually be observed.
The "mouthwatering" phase of the pass occurs in a roughly 48-hour period, centred mostly on the day-side of the object. Because New Horizons has to swivel to point its instruments, it cannot keep its antenna locked on Earth while also gathering data.
Controllers must therefore wait until later on New Year's Day for the probe to "phone home" a status update and to start to downlink some choice pictures.
And it will be 2 January before we see the first of these images, and 3 January before we get the best.
At a distance of 6.5 billion km, radio signals take over six hours to reach Earth.
"Our data rates are low - typical data rates max out around 1,000 bits a second and it's going to take 20 months to get it all back," explained New Horizons Principal Investigator Alan Stern. "Which is kinda cool because we'll be getting new presents from the Kuiper belt every week and every month though 2019 and most of 2020," he told BBC News.
What does New Horizons do afterwards?
The team working on the probe is going ask Nasa to fund an extended mission.
The hope is that the course of the spacecraft can be altered to visit at least one more Kuiper belt object sometime in the next decade.
It has just enough fuel reserves to be able to do this. Critically, it has sufficient electrical reserves to keep operating its instruments through this period, too.
New Horizon's plutonium battery may even allow it to keep talking to Earth as it leaves the Solar System.
The two 1970s Voyager missions have both now exited the heliosphere - the bubble of gas blown off our Sun. Voyager 2 has only recently done it, in November.
This occurred at a distance of 119 Astronomical Units (or 119 times the Earth-Sun distance, 149 million km). New Horizons is currently at 44 AU and clocking about three additional AU every year.
Its power system could probably run to about 100 AU, said Prof Stern.
"That's less than the Voyagers' distance but the interesting game is that the heliosphere breathes in and out by tens of astronomical units because of the solar cycle," he explained.
"No-one is good enough at predicting the solar cycle to tell you where the edge of the heliosphere will be in the mid-late 2030s when we go power-critical."
- RNZ, BBC