After New Horizons: Will Humans Ever Walk on Pluto?
On January 1st, 2019, the New Horizons probe will pass within 10,000 km of a relic of stone and ice left over from the beginning of the solar system. Ultima Thule, which means "beyond the known world", is the furthest object we've ever tried to study up close and marks successful end of the probe's career. Anticipating the fly-by on New Year's Day and inspired by New Horizons' original mission, the fly-by of Pluto in 2015, we explore what it would take to get a human crew to actually set foot on everyone's favorite dwarf planet and they'll find when they get there.
From Earth to Pluto: Distance Makes the Heart Grow Fonder
As the images came back from New Horizons in 2015, showing us Pluto for the very first time, the dramatic shots of the dwarf planet inspired the imaginations of billions. Having actually seen the dwarf planet up close, many must have asked what it would be like to set foot on Pluto.
We don’t have to rely only on our imaginations—having recently been there with New Horizons, we know a lot about the path a human crew would take and have worked out the math meticulously. New Horizons' biggest challenge was covering the distance from Earth to Pluto and ensuring the probe had what it needed to get there, but once that work was done and the New Horizons probe left Earth, everything else was programmed in so all we had to do was wait for it to get there.
A manned missions biggest challenge, meanwhile, is just getting off the planet we’re already on. To travel the billions of miles between Earth and Pluto, the amount of fuel you would have to bring with you isn't a major problem for New Horizons, but for a manned mission, it would be prohibitive. Chemical fuels are heavy and you eventually hit a limit on how much mass a rocket can lift off the planet. It's called the Rocket Equation, and there is no escaping its math.
Don't give up though. There is a way for us to get a ship capable of traversing the distance between Earth and Pluto off the planet. It’s just been sitting in a drawer at NASA for half a century.
Project Orion: Save Time and Travel to Pluto Like a Boss!
Project Orion is possibly the most heavy metal-inspired plan for humanity to ride off into outer space that anyone has ever come up with.
In the late 1950s, the space race was new, and so was nuclear power. Scientists were hard at work trying to get rockets into orbit, but this was also the early days of the space program where rockets twisted off in different directions before exploding fifty feet off the ground. Asking rocket scientists to build a rocket that could travel the distance between Earth and Pluto was a good way to get yourself laughed at and ignored.
Not for Freeman Dyson though. When the American aerospace firm General Atomic looked to Dyson, a renown British physicist, for help, all they wanted was a rocket that used nuclear power to get into orbit. What Dyson gave them has captivated the imagination of engineers ever since.
Project Orion, as the design came to be known, was a ship powered by atomic fire. By dropping a nuclear bomb behind the ship, setting it off, and repeating as necessary, you could ride the collective force of multiple atomic fireballs into the heavens like an absolute hellion. The only thing Project Orion doesn’t do is howl at the moon upon lift-off.
Not only that, but once in space, Project Orion takes full advantage of Newtonian physics. By building up momentum in a vacuum, the ship reaches speeds completely unattainable when using chemical propellant.
General Atomic wanted to get into orbit, but Dyson gave them a ship that could get them anywhere in Solar System. With one problem.
This ship would be an ecological catastrophe for the planet if it launched from the surface. Even people at the time saw that powering rockets with nuclear explosions would rain enough fallout into the atmosphere over time that it would poison the planet, so Project Orion never got off the ground. But what if there was a way around this problem?
Building secure structures in space aren’t new, we’ve done it with the International Space Station. Just like the ISS, parts of an Orion ship could ride conventional rockets into orbit. Once there, you'd only need to assemble it. Sure, it'd be outrageously expensive, and sourcing the nuclear material for all those bombs might be a problem, but it is possible.
Once completed, you’d have a nuclear-powered ship big enough to support a human crew. Using nuclear explosions to build speed, our crew could cover the 5 billion kilometer (3 billion mile) distance between Earth and Pluto in about 2 years. The round trip would take less travel time than it took for New Horizons to even reach Jupiter.
Overcoming Time and Distance, Pluto Would Be Within Reach
Now that we know it’s possible, in theory, to make it to Pluto and back, all that’s left is figuring out what to do when we got there.
We've always known that Pluto has a weak gravitational pull, but New Horizons confirmed that it's about 1/2 of the Moon's. With so little gravity, our crew would be 1/12 the weight they were on earth. A crew member weighing 82 kg (180 lbs) on Earth would weigh only about 7 kg (15 lbs) on Pluto. The ship would need to slow to about 800 m/s (2600 ft/s) to get into a stable orbit. Riding a wave of nuclear momentum, this is no small thing.
Since nitrogen ice covers much of the surface, a lander would have to find a flat stretch of rock set down, a challenge not that different than when we landed on the moon. There is little reason to believe that life could survive in the extreme conditions this far out, so unlike Saturn's moon Titan or other ocean bearing moons in the solar system, there's little worry about contaminating the surface. While there is data that suggests an ocean might exist under the surface ice, no one expects to find life on Pluto.
And if our crew isn't careful, they won't last long either. Almost 3.9 billion miles from the sun, the temperature hovers between -382 and -364 Fahrenheit (-230 and -220 degrees Celsius). No one knows what the climate would be like, but where there is an atmosphere, winds may reach as high as 230 mph (370 kph)
Our crew came prepared though, so as the first human to leave the lander sets foot on Pluto, they will see some amazing sights.
Charon, Pluto's largest moon, has a tidally locked orbit. This means that if our crew can see Charon from where they landed, it will never move across the sky. Charon is also much closer to Pluto than our moon is to Earth, so our crew would see a moon many times larger than ours looks when it is full. If a full moon on Earth is the width of your thumb relative to the observer, for our human crew on Pluto, Charon would appear as large as your fist in the sky.
It takes sunlight between 4.5 and 6.5 hours to travel the distance to Pluto, while it only takes 8 minutes travel time for sunlight to reach Earth. The difference in in intensity at these distances means that while staring at the sun on Earth is incredibly discomforting and dangerous, the diminished intensity of the sunlight on Pluto would be such that our crew could look right at it without discomfort. The sun would look like a normal star—only it would be 650 times brighter than anything else in the sky, something no human has ever seen.
Towering Razor Blade Ridges and Giant Spires
If the lander set down in the equatorial region, the dominant feature of the landscape might be gargantuan spires and bladed ridges made of methane ice. Rising as tall as skyscrapers, these might result from the seasonal sublimation of Pluto’s icy surface as it gets closer to the sun. The same process occurs on Earth, though at a much more reasonable scale of a meter or two.
New Horizons to Explore
Pulling together the resources something like this would be more than any one country could afford. Sadly, projects of this scale would require a collaborative international effort that is difficult to build in the best of times. But, if future humans can find the will, resources, and time to travel to Pluto, who's to say what we cannot do? After our crew finishes there, they might decide to keep chasing after New Horizons and give Ultima Thule a look too.
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