Monday, April 6, 2015

Re-creating a Giant

The main plot device in 2010: The Year We Make Contact is the transformation of Jupiter into a star. While most viewers accept the event as merely another plot device, some have taken it upon themselves to ascertain whether such an event would even be possible.


In the movie Jupiter is transformed by alien intervention into a ministar, the somewhat clumsily named Lucifer – a play on the mythical ’bringer of light’, as well as retaining the vowel flow of the original name.

[The name Lucifer has a long history in the Odyssey Universe, however. The very first drafts of the 2001: A Space Odyssey story called TMA-1 Lucifer. And this Lucifer was not a black slab, but a pyramid. But I digress.]

The slightly awkward name aside, the star in the movie shines just like we expect our own Sun to shine. Would this even be possible? Let us take a closer look.


Size comparison of Jupiter and a Brown Dwarf.


Before we delve into the specifics and get our hands dirty, let us establish a few facts by looking at what the stellar objects involved actually are. You might be surprised to learn there are few—if any—hard and fast borders between object classes in the Solar System, and thus by extension in the Universe.


Jupiter

Excluding the Sun, Jupiter is by far the most massive object in the Solar System. Out of the combined mass of all the planets the Jovian hunk gobbles a massive 77%, i.e. more than ¾ of the entire mass of the Solar System is contained in one single planet. Arthur C. Clarke even mentions this himself in the third installment of the Odyssey Sequence, 2061: Odyssey Three : the Solar System consists of "the Sun, Jupiter and some debris".

Jupiter's diameter is a whopping 142,796 kilometers (or 88,748 miles). That is 11 times the diameter of the Earth. The pressure at the center of the gas giant is 30,000 times the pressure at the center of the Earth. Indeed, the core of Jupiter is an Earth-sized center consisting of iron and silicates, surrounded by a shell of metallic hydrogen (hydrogen that has turned into a metal due to the immense pressure).

The chemical composition of Jupiter is incidentally quite the same as our Sun.

This is not cause for concern, it merely offers pause for thought.


Star Types

The Sun—also known by the Latin name Sol—is the central star of the Solar System, and is a typical G-type main sequence star. It alone amounts for 99.86% of the total mass of the entire solar system. There are other types of stars, as well, and for the purpose of this article we will focus on those.

The Sun is of course not the smallest possible star. There are much smaller stars—the so called red dwarves—that have roughly 7.5% the mass of the Sun's hydrogen. The problem is a red dwarf is still about 80 MJ (i.e. mass of Jupiter).

Exploding a star.

Red dwarves are the smallest stars that can maintain true fusion, characterized by fusing hydrogen into the heavier helium. There exists, however, another class of stellar object that are even smaller, the so called brown dwarves. A brown dwarf clocks in at a mere 13 MJ, and is nowhere near massive enough to give arise to hydrogen fusion. However a brown dwarf has enough mass to fuse deuterium, a variant of hydrogen.

To make matters more complex, there does not really exist any true and fixed boundary between a gas giant and a brown dwarf. Comparing a gas giant such as Jupiter to the smallest brown dwarfs reveals that they are essentially similar objects: the chemical composition is the same, the energy output is nearly the same, and remarkably the size is the same. To increase the confusion an additional class of objects has been added to the menagerie: the sub-brown dwarf, which is not really a star at all, but is considered by some a planetary body. Others state that a planet should be categorized as a sub-brown dwarf if is has been capable of fusion at some point during its lifetime. Perhaps interestingly, the smallest theoretical mass that could be classed as a sub-brown dwarf is equal to 1 MJ.

Perhaps it is not so wrong to call Jupiter a star, then.


Jupiter as a star

In the movie the moon Europa is portrayed as being in the habitable zone of the new star. This, of course, sets limits to the actual mass of the star. Europa orbits Jupiter at a distance of 0.004 AU (Astronomical Units); this unfortunately limits the mass of the new star to a maximum of 3 MJ. In order for Europa to maintain the orbit around the higher-mass body the speed of the moon would need to be increased, and higher speeds would cause unsustainable tidal forces within the satellite body. A larger mass star would need the moons/planets to orbit at such high speeds they would simply break up by tidal forces, considering their present composition. The limit of Lucifer thus seems to be rather rigidly set at 3 MJ.

Size comparison of Solar System objects.

If Jupiter could somehow be transmogrified into a star, it would not be much different from what it looks like now. A small brown dwarf does in fact not emit much more energy than Jupiter does at present. Jupiter already emits roughly 2.5 x as much energy as it receives from the Sun. The energy is "leftover" heat from when the gas giant was formed.

Jupiter as a sun would not shine as it does in the movie, either. While brown dwarfs do shine—after a fashion—the majority of the radiation that brown dwarfs emit are in the areas of the electromagnetic spectrum that have wavelengths either shorter or longer than that of visible light. Brown dwarfs do not glow for long, not even dully. When the deuterium is used up—which happens quickly—the brown dwarf transmogrifies again, and becomes a gas giant.

Do not worry, the cycle cannot repeat. There is no danger of Jupiter becoming a star every second million years.


Life on Europa?

If the moon Europa would lie in Lucifer's habitable zone after the cosmic transmogrification, in order to have a brightness similar to how bright the Sun is on Earth, Lucifer would need to be (0.004 AU/1 AU)2 = 1.6e-5 times dimmer. On Earth, Jupiter would appear to be a star ~(0.004 AU/4 AU)2 = 1e-6 times dimmer than the Sun, which would still make it the brightest object in the sky aside from the Moon. This brightness is impossible due to the mass limit set by the Jovian system itself, thus the new star would be dim indeed. Europa would be a dark, foreboding place.

Brown dwarfs emit high concentrations of ultraviolet light, however. This radiation is anathema to organic life, breaking down carbon compounds and whittling away any possible atmosphere any orbiting body may have. Ultraviolet radiation also breaks down any possible bodies of water into hydrogen and oxygen. With Europa’s mass being too small to retain hydrogen, causing it to escape into space, the radiation of Lucifer leaves Europa a dry, desolate body.

Coupled with the massive tidal forces heating the internals of the former moon, Europa would very quickly become utterly inhospitable and even more barren than it is at present.

Not a place for beach front property, clearly.


Conclusion

Even at our most charitable we must conclude that the scenario in the novel (and the movie) is not even remotely possible.

Even if we allow the monoliths to keep their magic properties, the laws of nature will put a stop to the nonsense in very short order. The scenario is poetic, and like most Clarkian fare ends on a hopeful, positive note.

We can however rest assured that it will forever remain poetry.



All images public domain.

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