Jupiter is much further from the Sun than Mars and is passed by the Earth every 13 months, so it’s brilliant in the night sky for much of every year. In a small telescope the four moons discovered by Galileo, all of them ‘mini-planets’ comparable in size to our own Moon or Mercury, change position from night to night as they orbit the planet. Look also for the flattening of Jupiter’s poles, due to its rapid rotation, and the dark ‘belts’ which are the true gaseous surface of the planet. The bright yellow bands are high-altitude clouds of ammonia crystals.
As Isaac Asimov said, “The Solar System consists of Jupiter plus debris”. Jupiter is more massive than all the other planets put together, one per cent of the mass of the Sun, and the only one whose barycentre (the centre of mass about which it and the Sun orbit) lies outside the surface of the Sun itself. In the first half of the 20th century there was a widespread belief that Jupiter was solid, but still hot from its formation; then that it was solid, but overlaid with ice. This was the ‘Wildt model’ of Jupiter, a metal core, overlaid with rock, overlaid with ice, which was widely endorsed at the time, e.g. in Patrick Moore’s Guide to the Planets (1957). James Blish’s classic story ‘Bridge’, expanded into the novel They Shall Have Stars (aka Year 2018) portrays an experimental engineering project on the supposed surface, remotely controlled, using different forms of ice formed at high pressures.
It had been known for many years that Jupiter’s atmosphere contains methane and ammonia, but the flyby probes revealed that it’s mostly hydrogen and helium. They also revealed that Jupiter has far more internal heat than expected, generated by the slow separation of helium towards the core of the planet which is still continuing more than four billion years after its formation. Jupiter’s outer core consists of hot superconducting liquid hydrogen, within which the magnetic field is generated, and the inner core is a solid lattice of hydrogen in metallic crystalline form with a temperature of 50,000 degrees. Most experts including Sir Patrick continued to insist that there ‘must’ be a further core within that of rock and/or metal, but two Pioneers, two Voyagers, the Galileo orbiter and flybys by Ulysses, Cassini and New Horizons all failed to detect one, although they found such ‘solid’ cores within Saturn, Uranus and Neptune without trouble. The current Juno orbiter has settled the question – there is no ‘solid’ rock or metal core down there, though there are denser regions within the crystalline hydrogen which may be the remains of asteroids captured during Jupiter’s formation. Jupiter really is a failed star: the increasing densities, inwards, of the four large Galilean moons, imply that Jupiter emitted still more heat in its early history and may even have sustained fusion reactions for a time, but they have long since failed for lack of sufficient mass to keep up the compression. Jupiter would have to be at least seven times more massive to persist as a stable star, 2010 notwithstanding. Some recent studies suggest 13 times the mass of Jupiter would be needed, and only deuterium fusion would occur even in brown dwarfs up to 75 times the mass of Jupiter (Volker Bromm, Matthew R. Bate, ‘Star Formation’, Physics World, October 2004).
If we could see the volume of space controlled by Jupiter’s gravitational field, it would dominate a large area of the sky. Even the magnetic field would be about the size of the Full Moon, if we could see it. It was thought that the trapped particles within it came from the Sun and from the volcanic inner moon Io, but with the discovery of water geysers on the ice-covered moon Europa (the Galileo probe actually flew through one in 1992, though it wasn’t realised at the time) the most likely source is water vapour, split into hydrogen and oxygen by ultraviolet light from the Sun, and then accelerated to near the speed of light by the fast-rotating magnetic field. The combinations of forces make the dense belts ‘supralethal’, where an astronaut would receive a lethal dose in a millionth of a second. The computers on the Pioneer 10 and 11 probes passing Jupiter were nearly swamped by false commands generated by the particle radiation, and later probes have mostly remained further out. Juno was to have gone in really close at the end of its planned mission, but due to a failure in the propulsion system it is still in fairly distant orbit, with a ‘go’ to continue studying the poles until 2025 at least. Precession of its elliptical orbit is now bringing its instruments within range of the giant moons, with a Ganymede flyby already achieved successfully.
When Galileo Galilei first published his discoveries he cast them as anagrams, to keep them secret while ensuring his priority. Johannes Kepler, who was not given the key, tried to decode them and came up with, “There is a red spot in Jupiter which rotates mathematically” and “Mars has two satellites”. He wasn’t so far wrong with the second reading, because Galileo was actually announcing his glimpse of the rings of Saturn, which he misinterpreted as two large moons. However, students struggling with Kepler’s Laws have been known to suggest that he should have stuck to solving anagrams instead of studying planetary motions!
Jupiter’s atmosphere is intensely turbulent, powered mainly by heating from below. As gas rises and falls, Coriolis forces in the atmosphere force it to into counter-rotating bands around the planet, passing each other at hundreds of miles per hour, with extreme turbulence at the edges. Punched through that are thunderstorms the size of the Earth, with intense lightning activity, and the largest, three times the size of the Earth, appears to be a ‘soliton’, a standing wave without which the whole system would be unstable.
The Great Red Spot is visible in six-inch telescopes, although a larger aperture is needed to show the colour. The storm has been visible since the 17th century at least, and passing space probes have seen temporary smaller ones. Most other storms on Jupiter are white and dominated by ammonia crystals, but the Great Red spot projects five miles above the rest and it’s thought that its colours are due to phosphorus compounds formed by solar ultraviolet radiation. Between 1998 and 2000, three large white spots merged to form a single spot which turned red in February 2006. The two spots passed each other on 13th July that year, riding different airstreams in Jupiter’s atmosphere, but didn’t seem to interact – that time. (Keith Cooper, ‘Red Spots’ Close Encounter’, Astronomy Now, September 2006). The Little Red Spot was photographed not long after it formed by New Horizons on its way to Pluto, and was re-imaged by Juno in August 2018, revealing a mottled structure like the GRS when photographed by Voyager 2, while the GRS itself now has a complex spiral structure as it continues to shrink. It used to be three times the size of the Earth, but is now ‘only’ twice that size, If like Highlander ‘there can be only one’, and they can interchange rôles, then maybe the smaller one seen by Giovanni Cassini in 1665 isn’t the one we have now, and maybe the Little Red Spot is destined to replace it – though it has now lost its colour, at least for the time being.
On approach to Jupiter the Galileo Orbiter released an entry probe, which entered the atmosphere at 50 km per second, decelerating at 230g, on 7th December 1995. It had been hoped that it would go down one of the ‘blue holes’ in Jupiter’s atmosphere, where water vapour can be seen in the depths and there’s the possibility of airborne life, but instead it went down a still deeper brown hole, a hot spot with no water at all. Contact was maintained for 57 minutes as the probe descended by parachute, to a depth of 130 km, at a pressure of 20 bars and temperature of 150o C. 300 km. down the parachute will have failed, and the aluminium components would have begun to melt 1000 km down at 1500o, with complete destruction 1600 km down, at a pressure of 1500 bars.
Early astronomers believed Jupiter must be inhabited. To quote John Grant, “Since God was universal and since simple living things must occur on other worlds (because of spontaneous generation), then so should more complex beings, all the way up to Man. But God had created Man in his own image. Thus other worlds must be populated by lifeforms identical with those of Earth… Huygens [after whom the Titan lander was named] believed that the fact that Jupiter had four moons (only the four Galilean moons had then been discovered) betrayed a plentiful supply of hemp on the planet. His theory was born from the popular fashion of finding design in all parts of the Universe. Clearly, the only purpose of Earth’s Moon was to act as a navigational aid. Now, since Jupiter had four moons rather than just the one, this must mean that there were a lot of seafarers there. Hence a lot of boats. Hence a lot of sails – and hence a lot of ropes with which to pull the sails up and down. But… to make a lot of ropes, you need a lot of hemp! QED.” So there must be a lot of places like Dundee on Jupiter. (A Directory of Discarded Ideas, Ashgrove Press, 1981).
In his books “Worlds in Collision”, et seq, Immanuel Velikovsky maintained that somewhere in the last 5000 years, Jupiter exploded and released a comet which sterilised Mars, wrecked Earth and became the planet Venus. At the visible surface of Jupiter gravity is about 2.5 g, and it isn’t possible for something the size of Venus to escape intact from something the size of Jupiter; even the old idea that the Moon split off from the proto-Earth is dynamically impossible. Although Velikovsky insisted there are no records of Venus prior to 1500 BC, there’s an unbroken sequence of Venus images in Mesopotamian art going back to 4000 BC. There is considerable evidence for catastrophe in the inner Solar System between 3000 and 2000 BC, including an impact in Iraq which gave rise to the Flood legend (see asteroid notes to come), but this is probably due to the break-up of a super-comet from the outer System.
80% of Jupiter’s composition in hydrogen, and 18% of the remainder is helium. Helium is named after helios, the Sun, because it was first discovered in the spectrum of sunlight, then in natural vents in Texas and Kansas (the first helium-filled airship was the US Shenandoah). The element exists in two isotopes with very different properties, both potentially useful to high-tech civilisations. Helium-4 exists on Earth in small quantities, released by radioactive decay. In liquid form it’s the coldest substance in the Universe, only just above Absolute Zero. It has negative surface tension, so it will climb out of an open-topped container and flow down the sides; it has superfluidity, so you can pump it both ways along the same pipe at the same time; and when used as a refrigerant it promotes superconductivity, reducing the resistance of electrical conductors to zero. So it has many possible uses, for instance in power transmission and many systems requiring high-energy magnetic fields, including radiation shielding for manned spacecraft. The superfluidity of liquid helium II was discovered, named and explained Peter Leonidovich Kapitza (1894-1984), at Cambridge in 1930-37 (Simon Mitton, Fred Hoyle, A Life in Science, Aurum, 2005). Kapitza received the Nobel Prize in 1978. Outside the Sun the largest repository of helium is in the atmosphere of Jupiter, and Isaac Asimov suggested that helium would be the planet’s major export to the Solar System. (‘The Element of Perfection’ in View from a Height, Dobson, 1964).
However the lighter helium-3 may prove to be even more important. If we ever master controlled fusion, for energy generation or spaceship propulsion, the most promising reaction seems to be the fusion of deuterium (heavy hydrogen) with helium-3. The theory was examined in detail by the British Interplanetary Society’s interstellar probe study, Project Daedalus (BIS, 1978). Deuterium is plentiful on Earth, particularly in sea-water, and Helium-3 is found in small quantities in solar wind deposits on the lunar soil, but claims that it could solve the USA’s energy problems seem highly questionable. To meet even 10% of the US energy requirement, so much lunar soil would have to be strip-mined that the scar would become visible from Earth with the naked eye, in only three years! (America at the Threshold, Report of the Synthesis Group on America’s Space Exploration Initiative, US Government Printing Office, 1991.) Helium-3 can be manufactured in nuclear reactors, but that would generate so much waste energy that the plant would have to be on the Farside of the Moon to protect the Earth!
In ASTRA’s Interplanetary Project, leading to my books “New Worlds for Old” and “Man and the Planets” (1979 and 1983), we realised that there was an easier way to get at Jupiter’s resources. Project Daedalus studied how an interstellar probe could be sent within 60 years – a human lifetime – to Barnard’s Star. The propulsion system was to be ‘pulsed fusion’ and the 50,000 tonnes of deuterium and helium-3 required was to come from the atmosphere of Jupiter (A.R. Martin, ed., Project Daedalus, British Interplanetary Society, 1978.). Gregory L. Matloff then pointed out that the same propulsion system could be used to make Gerard K. O’Neill’s proposed space settlements mobile, to reach Alpha Centauri in 430 years (‘Utilisation of O’Neill’s Model 1 Lagrange Point Colony as an Interstellar Ark’, Journal of the British Interstellar Society, Dec.1976), and I discussed the implications in the JBIS ,Sept. 1983, and in Analog, ‘Project Starseed, or, Nuclear Waste Saves the World’, (Feb. 1985) and ‘Fermi Paradox – the Final Solution?’, May 1986.
In the BIS proposal, the factories to concentrate the Daedalus propellants were to be ‘aerostats’, huge hot-air balloons (R.C. Parkinson, ‘Propellant Acquisition Techniques’, in “Project Daedalus”, op cit) – minimum diameter 212 metres, to support 85-tonne nuclear-powered factories. With 10% excess lift capacity, it was calculated that they could beat the downdraughts of the dark belts, which would be of order 25 metres/sec.. Arthur C. Clarke described a similar vehicle for Jupiter research in the story ‘A Meeting with Medusa’. To keep outside the radiation belts the operation would be conducted remotely from Callisto, the outermost of the Galilean moons, and this was why Nigle Calder’s Spaceships of the Mind (BBC, 1978) envisaged future conflict between Earth and Jupiter for the resources of the Asteroid Belt.
However, to expect nothing worse in the atmosphere of Jupiter seems optimistic, and Gordon Ross and I decided to use a Waverider instead, with a variant of the spacecraft designed by Prof. Terence Nonweiler at Queen’s Collge, Belfast, in 1962. With 290 kph airstreams meeting in opposite directions, the Voyager photographs in 1979 showed turbulence features typically 100 km across, and above the visible clouds Clear Air Turbulence may be extensive. This once dreaded killer on Earth can now be detected by radar, but over Jupiter only powered aircraft may be able to avoid it. At Mach 6, which was the design speed of the Royal Aircraft Establishment Waverider airliner (J. Pike, ‘Efficient Waveriders from Known Axisymmetric Flow Fields’, NASA/University of Maryland 1st International Hypersonic Waverider Symposium, 1990), an aircraft would simply slice through turbulence in any case. If the factory maintains that speed, incoming shuttles won’t have to slow down any further (the shockwave typically detaches from a Waverider leading edge at around Mach 2.4), and more importantly outgoing shuttles will not have to use so much of the fuel they came for, to get away.
Docking and undocking shuttles, in a gravity 2.535 times Earth’s, will paradoxically be easier with a factory in powered flight than with the underside of an aerostat which will be stationary in its airstream. Gordon designed a Waverider flying factory with a docking boom on top of the fin, approached as in mid-air refuelling on Earth, so that the shuttles don’t have to enter the shockwave over the factory’s upper surface. (Duncan Lunan, Man and the Planets, Ashgrove Press, 1983; Duncan Lunan and Gordon Dick, ‘Flight in Non-terrestrial Atmosphere, or the Hang-glider’s Guide to the Galaxy’, Analog, January 1993; Duncan Lunan, Incoming Asteroid! What could we do about it?, Springer, 2013.)
In Jupiter’s atmosphere there’s chemical energy potentially available, with a great deal of free hydrogen. Chlorine could be used, as in the Mesklinites’ flame-throwers in Hal Clement’s novel Mission of Gravity; a chlorine jet would be hypergolic (igniting on contact) in Jupiter’s atmosphere. However, the reaction would only work in sunlight, and at Mach 6 the Waverider isn’t fast enough to keep up with Jupiter’s whirling rotation. If the shuttles are coming in from Callisto, as the BIS team planned, then they can bring in oxygen to use instead, from the ice on that moon; there is oxygen on Jupiter, in the water-droplet layer which we see through ‘blue holes’ in the dark layer, but it’s a long way down. But most probably the factory would be fusion-powered, since the factory is refining the fuels needed, and that will need a lot of onboard energy.
An extra large engine intake would also bring in atmosphere for processing. Thereby, at Mach 6, the factory eliminates or at least reduces the load on the compressor which is the first stage of processing on the aerostat. The gases then have to be liquefied in a compression turbine, then treated in a fractionating column to take off the ordinary hydrogen. On Earth that column would be at least 12 m. high (R.B. Hinckley, R.C. Reid, P.E. Glaser, ‘Recovery of Deuterium in the Atmosphere of Jupiter’, Second Conference on Planetology and Space Mission Planning, Annals of the New York Academy of Sciences, 163, Article 1, 1-558). Jupiter’s gravity may be some help, but it gives an idea of how big the factory has to be. Further treatment would then be needed to separate the deuterium from the helium and the helium-3 from the ‘normal’ helium-4; but those stages might be done in space, if industrial uses of helium-4 made it worth shipping out from Jupiter, as Isaac Asimov suggested (see above).
Otherwise, shipping out is enough of an undertaking to make it worth shedding all unwanted mass. From the upper atmosphere, to get into close orbit around Jupiter takes 42 kps, and to escape altogether needs 60 kps, but Jupiter’s 12.6 kps equatorial spin provides a quarter of the orbital velocity and a 290 kph airstream in the same direction supplies 0.08 kps; hypersonic factory flight can add up to 3 kps more. A shuttle can reach 10 kps in the atmosphere on scramjet thrust before engaging rockets, but a further 19-20 kps is still needed to reach orbit, while the transfer to Callisto is equivalent in energy terms to an interplanetary mission.
The BIS team specified Callisto as the base of operations because it’s the only one of the large moons outside the radiation belts. But space habitats’ shielding against cosmic rays will allow them to come into close orbit around Jupiter. The energy required to get there is nothing to a habitat which is fuelling up for the journey to the cometary halo or one of the nearer stars. Gordon assumed that before pickup the factory accumulates 60,000 lbs. of cargo, a typical payload for the present Space Shuttle, needing 1800-2000 flights to accumulate 50,000 tons of propellant. Ideally the shuttles would be a nuclear-powered version of Alan Bond’s HOTOL, more suitable for this purpose than his more recent Skylon design.
Because Jupiter’s magnetic field is generated not in the core, but in the liquid hydrogen layer overlying it, the field isn’t concentric with the planet. There’s an ‘eccentric cam effect’ – a radiation-free zone, extending to 7140 km above the clouds on one side of the planet, rotating with the invisible ‘System III’ of Jupiter’s interior. From a habitat in it, a manned, unshielded vehicle can descend into the atmosphere. Operations would normally be automated, but living space for a crew of two in the factory nose, with access from the fin, allow emergency repair. The factory’s wing-loading allows for extended glide at below design Mach number, for that. If it fails and the crew can’t get back to their shuttle, the escape system for’ard might be a capsule with a deployable hot-air balloon.
Would anyone go down there, willingly? At the visible surface gravity is 2.55 g; but standing up in a fairground rotor is a common test of strength, and aerobatic teams perform sustained sequences at higher g-loadings. Pilots could be acclimatised to it in centrifuges, or just by driving round the axis of their habitats at high speed, as the Skylab astronauts simulated gravity by running round the ring of lockers. With 90 km-deep sky to play around in, there are bound to be pilots who find some excuse to get down there. However, they could probably adapt to higher gravities: it’s been done with chickens raised in centrifuges under simulated Jupiter gravity (Ed Regis, “Great Mambo Chicken and the Transhuman Condition”, Viking, 1980).
As an ultimate extension of these ideas, in “Man and the Planets” we envisaged Jupiter being terraformed by converting enough of its hydrogen into oxygen, with flying fusion reactors, to turn it into a huge ball of water. As the Chinese proverb has it, “with sufficient fire you can cook anything”. There could be a civilisation living in lagoons, with giant lily-pads, kept open in the ice by sub-surface fusion power plants. That image had come from a BBC documentary about life on the Amazon; the real-life ones are Victoria Regia, featured in David Attenborough’s The Private Life of Plants. We suggested that to avoid becoming indolent the inhabitants should regard serving on the wind-power generators, mounted on the surrounding ice walls, as a form of National Service; otherwise there would be a danger of evolving into two distinct forms, like the Eloi and Morlocks of “The Time Machine” – putting a whole new complexion on the words, “Come with me and I will make you fishers of men”.
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