This is it. After a journey of more than nine years and 3 billion miles (4.8 billion kilometers), NASA's New Horizons spacecraft will finally arrive at Pluto tomorrow.
If you aren’t excited, you should be. For many people, this will be the only time that a world as significant as Pluto will slowly come into view and then be captured in images by a spacecraft. Only future generations that possibly explore other dwarf planets in the outer Solar System or perhaps planets beyond will experience anything quite like it.
"After nine and a half years in flight, Pluto is well worth the wait," New Horizons principal investigator Alan Stern said in a statement from the mission operations center at the John Hopkins University Applied Physics Laboratory in Laurel, Maryland. For those that were around to see it, the last time something of this magnitude occurred was in 1989, when Voyager 2 flew past Neptune.
Last night at 11:23 p.m. EDT (this morning at 4:23 a.m. BST), New Horizons moved within one million miles (1.6 million kilometers) of Pluto, speeding towards the dwarf planet and its five moons at 30,800 mph (49,600 km/h). It will arrive tomorrow at 7:49 a.m. EDT (12:49 pm BST), although owing to the vast distances involved and a one-way communications time of 4.5 hours, we won’t know if it has been successful until the end of the day. The first signals and data are expected back at 8:53 p.m. EDT Tuesday (1:53 a.m. BST Wednesday).
Artist's impressions like this are all we've got to go on right now, but by tomorrow we'll know what Pluto and Charon really look like. Credit: NASA/JHUAPL/SwRI
Despite the long journey time, the flyby will last just over two hours. The best images can be expected on Wednesday, but it will take 16 months for all of the data taken by the spacecraft to be sent back to Earth. This is due to both the distance and the low bit rate of the spacecraft, which has the ashes of its discoverer Clyde Tombaugh on board.
New Horizons will perform hundreds of tiny movements during its pre-programmed flyby to observe Pluto, Charon and the other four moons: Hydra, Nix, Styx and Kerberos. Some glamour shots of Pluto will be among the first data that are sent back, considering the public excitement surrounding the mission. Much more data concerning the solar wind at Pluto, its composition and so on will be gathered by the seven instruments on board the spacecraft and slowly fed back to Earth over the next few months.
During the flyby, the spacecraft will come as close as 7,800 miles (12,500 kilometers) from Pluto. For comparison, one of the most famous shots of Earth, The Blue Marble, was taken by the Apollo 17 crew from a distance of 28,000 miles (45,000 kilometers). The images that we'll see of Pluto – which is two-thirds the size of our Moon – will be 300 times better than anything seen of it at the moment.
Several intriguing geological features have already been spotted on Pluto. Credit: NASA/JHUAPL/SWRI
Among the science hoped to be gleaned, scientists will attempt to spot signs of an atmosphere on both Pluto and its moon Charon. As the spacecraft shoots past, it will look back and observe the Sun’s light coming through the atmospheres belonging to these bodies. It will also view the night side of Pluto as lit by Charon, which appears about as bright as the full Moon does on Earth in the sky.
One of the big surprises so far has been the differing appearance of Charon and Pluto. The former has an unexplained dark region at its pole but is otherwise mostly grey, while Pluto seems to be more red. Considering that they were thought to have both been influenced by an early collision, this difference is strange. Also on Pluto, possible cliffs have been spotted, and its geology is starting to prove fascinating. One particularly interesting feature is a darker region shaped like a "whale’s tail."
Many such features and more will be observed up-close by New Horizons. For the most part, what we'll find remains a mystery. Features we definitely won’t see, though, include the mysterious "dark spots" on Pluto’s equator. Owing to the relatively short flyby, this feature will have rotated out of view of New Horizons.
New Horizons, artist's impression shown, launched atop an Atlas V rocket back in 2006. Credit: NASA/JHUAPL/SWRI
The excitement is now reaching fever pitch, especially considering at present there is no other mission to Pluto planned in the future. And despite the long journey time and extensive number of operations that will take place at the system, there is much science that will go unanswered. Astronomer Mike Brown, famed for the discovery of fellow dwarf planet Eris that led to Pluto being demoted from the ninth planet of the Solar System, tweeted: “Amazing how fast this is all going to come and go and how much we will wish we saw but didn't.”
Hundreds of Pluto-sized objects are thought to be in the Kuiper belt at the edge of the Solar System, one or several of which New Horizons will explore after Pluto. For now, though, it's time to sit back and prepare for one of the most exciting moments in the history of space exploration. Eighty-five years after its discovery, Pluto is finally about to reveal its secrets.