You have all seen the spectacular footage of Felix Baumgartner’s jump from stratospheric heights. What a spectacular feat: technology, human courage and the beauty of the breathtaking view from the stratosphere converged into a few very special minutes. Now, the feat is done, the man has touched down in one piece, and the post-jump party is over. What could be next? How about jumping from the stratosphere of another planet? While we are at it, let’s chose the solar system’s planet with the largest atmosphere and the strongest gravity: Jupiter!
This is certainly not a realistic short-time proposal! But while it might take centuries for a jump from Jupiter’s stratosphere to become doable, we can let our imagination fly in the meantime. I will use our current knowledge of the Jovian atmosphere and of human physiology to outline what we would have to do to make it happen. It’s a fun thought experiment!
First of all, of course, we would need to have interplanetary travel to the location of our jump. Sure, this is not an easy task, but rather one with lots of issues to solve. However, humans have walked on the moon, spent over a year continuously in space, and sent unmanned spacecraft to Jupiter. So while we haven’t put a person near Jupiter yet, in principle this seems to be achievable. I won’t dwell on the commute to the jump any further, but speculate if and how the Jovian stratospheric jump itself would go.
As on earth, the first phase would have to be an ascent to the upper layers of the atmosphere. Felix Baumgartner used a helium balloon to reach his jumping altitude. This works on earth, because our atmosphere is mainly composed of nitrogen and oxygen, two gases denser than helium. The low-density helium, captured in the balloon, rises and allows an upward journey for a terrestrial skydiver. But the atmosphere of Jupiter is made up of hydrogen and helium – and hence is on average less dense than the helium in Felix’ balloon. A large polyethylene bag full of helium would sink on Jupiter like a salt-water filled bag in a freshwater swimming-pool. The Jupiter-Felix of the future will have to find another way to make his way up. There is no gas in existence which is less dense than the hydrogen which the majority of the Jovian atmosphere is composed of. A pure hydrogen balloon would be slightly positively buoyant on Jupiter – but probably not enough to lift a capsule with a skydiver, at a reasonable balloon size. Equally, a hot-hydrogen balloon would only work in the lower, denser layers of Jupiter’s atmosphere. A rocket might be the way to go up.
But where on Jupiter would we want to send our man up? Many of us still remember the nerve-wrecking delays to Felix Baumgartner’s jump, caused by some unfriendly winds in the Roswell, New Mexico area. Strong wind is simply not conductive for extreme skydiving. And if there is one place with strong winds in this solar system, it’s the atmosphere of Jupiter. This is a place with storms several times the size of earth. The Great Red Spot, the largest of them all, has been going on for at least 300 years. In addition to the hydrogen and the helium, which make up most of Jupiter’s atmosphere, methane, ammonia, hydrogen sulfide and water contribute to the volatile weather. Temperature-convection movements and differential rotation between the gases in the equatorial and the polar regions fuel the biggest theater of gas dynamics between Mercury and Pluto. An expert team of Jupiter-meteorologists will have to work very diligently to find the calmest possible spot in this wild Jovian atmosphere. Is it even possible to find such a spot? This is impossible to predict with any certainty a century before the assembly of this team, but I want to remain optimistic!
I warned you – this is not golf on Mars (easy: low gravity and no trees) – but an exceedingly complicated and challenging endeavor! So, now that we have Jupiter-Felix ready to jump, what will happen next? Just like Earth-Felix in 2012, he will accelerate downwards, courtesy of the universal forces of gravity. But since gravitational acceleration is a consequence of mass, and Jupiter’s mass is ~318 times that of Earth, its gravitational force is about 2 1/2 times what we are used to at home (24.79 m/s2 versus 9.78 m/s²). This increased gravity would have some potentially dangerous consequences: Jupiter-Felix would accelerate to higher speeds, with a higher likelihood of developing a dangerous spin. Stabilizers, like the fins on the tails of rockets, might be an unconditional necessity for high-altitude skydiving on Jupiter. The fall could be incomparably more risky than any skydive on Earth.
Now on Earth, once Felix Baumgartner had deployed his parachute, the most dangerous part of his jump was over. What was left was to dangle below the parachute, and eventually set foot on solid ground. But on Jupiter there is no solid ground! On this gas giant the atmosphere transitions into a liquid and then metallic hydrogen core without a distinctive boundary. The hydrogen/helium pressure will continually increase the longer Jupiter-Felix falls, until the density of the atmosphere becomes equivalent to the density of his body, at which point he stops descending. Or, rather, at which point his charred remains stop descending. Because, in concert with the atmospheric pressure also the ambient temperature increases.
Why do we know that? Because a similar descent had been done by an unmanned space-probe. In 1995, the Galileo atmospheric entry probe descended into Jupiter’s atmosphere until it reached a point where 23 atmospheres and a temperature of 153 °C incapacitated its transmission system, and the contact with the Galileo orbiter was lost. Such a temperature would definitely kill any human. And hydrogen gas at 23 atmospheres has not nearly the density of a human’s body, so this equilibrium point would only be reached much deeper, at even higher, completely intolerable temperatures. Our Jupiter-Felix of the future would have to have a system to completely halt his descent before he reaches such hellish conditions. Merely slowing down his fall with a parachute would not be enough. Again, rocket boosters sound like a very good idea here.
In the absence of a real planetary surface, earthist scientists have arbitrarily designated the layer with 1 atmosphere of ambient pressure as the surface of Jupiter – just like the pressure on Earth’s surface. While it would prove deadly to fall to a vastly lower level, where the temperatures rise unbearably, it is not necessary to stop at the altitude where the atmospheric pressure is 1 atmospheres. The Jovian free fall can continue well below that level.
Now, Felix Baumgartner had to bring a supply of oxygen to breathe for his record breaking skydive. At an altitude of 39 kilometers, there is simply not enough of it in the atmosphere anymore for a human to survive. Future-Felix would have to do the same: even in the thicker layers of the Jovian atmosphere, there is no oxygen at all. In the early phase of his fall, in the upper layers of the Jovian atmosphere, he could breathe the pure oxygen he brought along. But as soon as he falls below the layer where the pressure exceeds 1 atmospheres, he has to be careful. Breathing oxygen at a pressure of more than about 1.6 atmospheres is dangerous!
I am assuming that our future extreme athlete is wearing a flexible pressure suit similar to the one Felix Baumgartner wore. This means that when he encounters excess ambient pressure, he needs breathe gas at that pressure. Otherwise he would run the risk of having his lungs crushed. In a sense, his situation becomes similar to that during a scuba dive, where the breathing gas must be of the same pressure as the ambient water pressure. Scuba divers typically breathe air, with an oxygen content of 20%. At a depth of about 70 meters, when the ambient pressure is 8 atmospheres, the partial pressure oxygen reaches 1.6 atmospheres (20% of 8 – equivalent to 1.6 atmospheres of pure oxygen) and oxygen becomes very toxic. Anyone breathing air at such a pressure runs the risk of a sudden seizure – there is a very grizzly video on Youtube of a guy with a helmet-cam having such a deadly experience. Hence, once Jupiter-Felix falls below the level of the Jovian atmosphere where the ambient pressure reaches 1.6 atmospheres, he can’t breathe pure oxygen anymore. It will be necessary that he then starts diluting his breathing gas with the helium and hydrogen of Jupiter’s atmosphere.
So, is a stratospheric jump on Jupiter simply not doable? Certainly, it would be a very challenging project. We currently don’t have the technology to do it, yet. But I am hoping for continued technological progress driven by human imagination and the desire to push boundaries. Red Bull Stratos II: Jupiter? I definitely hope to watch it sometime as an old man! Earth is a nice planet (and I am a strong advocate of not messing up its biosphere). But the intensity of our planetary home’s weather can’t keep up with the atmospheric spectacle of Jupiter’s atmosphere. A freefall through these erratic layers of gas would certainly provide some utterly amazing views. I really hope somebody will do it!