G'day and welcome to another edition of Ask ARSE.
The space where followers of ARSE come together and prod us for answers about the deep unknown.
Today's question comes from a special friend in our Australian Space Society.
The nature of the gas giants in our solar system is a hefty steak to chew.
Particularly the giantest gas giant and fifth planet from the sun, Jupiter.
But let's get to the question first and attack the blanks after.
"Hi ARSE. If Jupiter is a flammable gas giant can we light it on fire with enough power like a massive nuclear warhead? I read your blog about brown dwarf stars and if Jupiter lit up would it turn into one? Cheers for the sweet memes and the cool gear." - Aaron, Perth.
Well thank you for the kind message Andrew.
Firstly, let's look at Jupiter and really get to know what it is from the outside in.
What is Jupiter?
Although Jupiter is the largest planet in our solar system at two-and-a-half times the mass of all the planets combined, it's mass is only one thousandth of our sun. Although Jupiter's size is equivalent to 1,321 Earths, it's mass is only equal to 318 Earths.
Why?
It's makeup is primarily hydrogen, which might get your nuke senses tingling, but don't jump the gun just yet. Around one quarter of Jupiter's mass is helium, which is less dense than air and not flammable. The core of Jupiter is expected to be a rocky, metal mass even though the outermost parts are not a well-defined, solid surface.
Each Earth year, Jupiter's size decreases by about 2cm due to compression of its core.
Funnily, if Jupiter's mass grew by 60%, its size would shrink considerably. Its core would stack on more pressure and compress the planets insides further, making the volume of Jupiter decrease.
Generally, as far as planets go, the smaller the core the larger the gaseous outermost parts.
The gassy planetary atmosphere is the largest in the solar system at over 5,000 km in altitude. Because it has no surface, the base of its atmosphere is universally agreed upon as the point which atmospheric pressure is equal to 100kPa.
The clouds over Jupiter are made from ammonia crystals and possibly ammonium hydrosulfide. The long, gassy bands around Jupiter are tell-tale signs of different latitudes or tropical regions. They're then divided again into two classes; darker parts called belts and lighter ones called zones. The conflicting patterns of belts and zones cause violently turbulent weather with wind speeds of up to 360km/h.
But for the purposes of this question, Jupiter is a comparatively teeny rock with a mixed layer of gases around it, despite it looking like a space goliath.
Pictured: A brown dwarf
What is a star?
Stars are objects consisting of a plasma sphere held together by its own gravity.
Stars are formed when a gravitational collapse of hydrogen and helium and trace amounts of heavy elements. When the core of a potential star is dense enough, hydrogen consistently converts into helium through nuclear fusion while the soon-to-be-stars interior carries heat away from the core. The stars internal pressure prevents collapse under its own gravity and should the star be around 40% larger than our sun it will become a red giant.
Red giants are formed when hydrogen fuel in its core is expended and begins to fuse heavier elements in its core. Eventually, a red giant will become either a:
- White dwarf - a star with the density of our sun but the size of Earth
- A neutron star - a collapsed core
- Or if the star was big enough, a black hole
A red dwarf is a considered a "true" star burning hydrogen to helium. So Jupiter does have the early prerequisites of a burning star. Red dwarfs are accepted as the smallest and coolest version of a true star.
But wait... There's more.
A brown dwarf has limited burning capacity and has limited fusion of trace deuterium (one of two stable isotopes of hydrogen) only. Unlike other larger stars, brown dwarfs do not have the ability to trigger sustained nuclear fusion of hydrogen into helium in their cores. This is why they're often referred to as failed stars.
They're almost stars.
Can we turn Jupiter into a star with a nuclear warhead?
So, can we turn Jupiter into a low-mass brown dwarf star using a thermonuclear warhead?
No.
Can we turn it into a true star, like a red dwarf?
Not even close.
The nuke isn't the problem, it's the mass of Jupiter.
It's simply too small to sustain even the smallest nuclear fusion reaction.
It's like trying to spark a lighter in the wind.
While most brown dwarfs are slightly smaller than Jupiter, they are still upwards of 80 times more massive.
They're hardly packed, compressed and the pressure of their atmosphere is enough to chain a massive reaction like an exploding LPG gas bottle. Jupiter is simply too "fluffy" with not enough atmospheric pressure.
When brown dwarfs are ready to turn into a red dwarf there is no stopping them.
Forcing a gas giant into a brown dwarf is almost impossible without density and pressure.
We'll let a friend, George Dowson from the University of the United Kingdom explain in technical detail:
In very brief - in order for fusion to happen, the positively charged nuclei of to atoms have to be brought close enough together that the nuclear strong force (which has a range of up to 3 femtometres or 3 millionths of a nanometer!) to bind them together. At that 3 fm distance the electrostatic repulsion of two positive charges is enormous.
If you brought two protons within just 10 femtometres of each other and then released them, you’d have to factor in relativistic motion as they would accelerate apart at a rate of 688,622,754,491,018,000,000,000,000 m/s^2. If they weren’t limited by the speed of light and kept up this acceleration for 1 second, they’d be going 2.3 quintillion times the speed of light at the end of that second. Or fast enough to cross the visible universe in 1.2 seconds.
(In a real event, this acceleration only happens for a fraction of a nanosecond and drops off rapidly, but safe to say, they fly would apart at insane speeds. And of course they cannot exceed the speed of light in any event.)
The only way to overcome such a huge repulsive force is to have the nuclei moving so fast their momentum overcomes the repulsion (like throwing two repelling super magnets together fast enough they hit despite the repulsion), or by compressing them so much they are forced together (like using a hydraulic press to force two super magnets to touch).
In a hydrogen bomb, fusion occurs when the pressure and temperature reaches 50–100 billion atmospheres and 100 million Kelvin. In the centre of the sun, the pressure (caused by the gravitational mass of the sun) is actually higher - at around 250 billion atmospheres, allowing a lower fusion temperature of 15 million Kelvin.
Keeping the units the same, the temperature and pressure at the centre of Jupiter is just 0.1 billion atmospheres and 0.025 million Kelvin. Too small and too cold.
To become a low-mass brown dwarf, Jupiter would need to be at least 13 times more massive in its current state. Anything lower than this and Jupiter is in the grey area of being a sub-brown dwarf - or a nearly an almost failed star - or a gas supergiant as it is.
Although Jupiter would need to be about 75 times as massive to have a fusion reaction and become a full fledged star, one red dwarf discovered is only about 30% larger than Jupiter.
How?
Again, it's density.
The red dwarf mentioned is far denser than Jupiter despite its size.
Even so, Jupiter still radiates more heat than it receives from the sun through contraction, the same reason it shrinks by 2cm every Earth year. When it was formed, Jupiter was much hotter and approximately twice the size we see it today.
Thanks for the question mate and being a ripper member of the space society.
Please share with a mate to spread ARSE!
#Space_Aus
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