IT is commonplace fact in life — or the universe — for one item to be bigger, or smaller, than the other, even far bigger or far smaller in dimensions. But being bigger (or larger) by as much as 318 times is wholly uncalled for.

As you already know, planet Jupiter is 318 times larger than Earth. That is, it is more massive by that much. That is massive disparity! A group of scientists think that Jupiter is not a planet but a brown dwarf (a small ‘unlit’ star). It is akin to saying that blue whale, or an elephant are not animals but demons because their size just does not conform to worldly dimensions. We will return to it a little later.

Jupiter, as we know, is all clouds. Clouds of ammonia and methane crystals, with a small core to boot. The core is undoubtedly small, but stay put! It is still 15 Earths big. In the aspect of sizes and dimensions, planet Jupiter takes the cake ! Nothing in the Solar System can lay a similar claim. It alone occupies a whopping 71 per cent of all planetary material of the Solar System. Its thick atmosphere of hydrogen, helium, ammonia and methane reaches up tens of thousands of miles above the surface.

Despite being a vast way up, this really explains nothing unless you understand the basic fact that the gasses are highly concentrated as they build up near the surface and gradually become less concentrated with increasing altitude. Call them tenuous as they go up. It implies that for the first (say) 10,000km their volume may be the same as the last 10,000km but it has much more gas comparatively — meaning it is dense (the molecules and atoms are compressed). Scientifically speaking, the first distance stated above has a lot more molecules packed together than the last quoted, although the area remains the same. On Earth the same analogy is dealt with on a much smaller scale.

Tiring, is it ? But if you grasp the basics it becomes easier as well as enjoyable as you proceed further. More about Jupiter will prove my point.

Jupiter has been losing heat constantly since its birth, which was about 4.6 billion years ago! But the question is: how it continues to have that heat, or why it continues to spew out heat without let or hindrance? The first reason lies in the heat left over from the time the planet was formed, which is true for any planet except for the fact that smaller planets, on account of their low and insufficient gravity, failed to retain their intrinsic heat and gasses which were lost into space gradually, but inexorably. On the contrary Jupiter could hold on to its original stock and lost a very small amount as a consequence of various factors. At the same time, it replenishes what it loses. But the rate of loss is slightly higher than retention and that is why the planet contracts slightly with the passage of time, producing more heat in the process (interesting that as it contracts in size it becomes hotter). In a sense, its formation is still in progress. It might yet take a few million years before it blooms into full maturity. Maybe half a billion years or more.

The core of Jupiter consists of dense material like planet Earth. It is commonly called the rocky core, but high temperature and intense pressure deny the existence of similar material as in Earth’s case. It’s core is thought to be a hot mixture of iron, nickel, silicon and other heavy elements which gradually sank towards the centre, while lighter material and gasses floated (actually seeped) upward to form crust of sorts, as is true for all planets.

An important question of far reaching consequence has arisen: which way does heat travel? This question is of prime importance wherever the transfer of heat, or temperature is involved. And throughout the universe, in every nook and cranny, in all bodies big or small, whether dense or tenuous, hot or cold, the transfer of heat is taking place at every moment, in fact at every split second of the time invariably, without let or hindrance. But in which direction?

We observe the tea boil, we also see a cube of ice melt, then we observe the mighty Sun warm the Earth, likewise we know that the ocean warms up and the upper layer of water is warmed sooner and forms into clouds which eventually fall back on Earth in the form of rain, precipitation or snow. Things are happening — forever and at all times of the day or night, even in the middle of a hurricane or a blizzard. But remember that heat only and only travels in one direction: from hot to cold. Never from cold to hot.

I remember when, as an expression of disagreement, I argued with my science teacher way back in school. To make my point, I stated that ice melts and in doing so gives off its cold. He was wise and showed a lot of patience. It appeared that I triumphed in my argument — but it was short-lived! He said that in the act of melting, the ice is giving off heat, whatever heat it has. And it is ‘joining’ the surrounding region by equalling its temperature, for what is temperature save the amount of heat a body contains. In short, ice was not giving off its cold, instead it gave off its heat to be at par with the surrounding atmosphere.

Now the question, how come Jupiter, and for that matter, all four of the gaseous planets each have so much gas, but the others have so little. There is more than one reason for that. However, we will only take a look at one right now. As planets began to develop crust (the uppermost layer) their own action led to gradual breaking up of the surface of the crust.

It is common knowledge that when cooked at home, a pie or bread or any similar item develops a crust that cracks up a little after a while. At home, I say because professional cooks make sure that cracking or chaffing does not take place. In short, when the cracks appear in the newly formed crust of a planet with insufficient gravity it gives vent to the trapped gasses, chemicals and water, yes water! When that happens they escape, and escape rapidly. At this point in time gravity plays its part.

But in the case of smaller planets, as we know, gravity is not enough to trap them, or arrogate to themselves their own escaping matter. So that it is a huge volume of gas with nowhere to go. It is now up for grabs. Whoever wants it can have it for free. The Jovian planets being big and huge, with an irresistible gravitational field have the last laugh. The escaped matter, gravity and time permitting, has enough opportunity to form an envelope around the mother planet, yet they escape like a trapped animal suddenly let loose. When that happens, they are free to be scooped by the next planet. That being Mars — itself small and insignificant from the point of view of gravity, and which itself is going through the same process as the other planets and in all probability moons are, these planets have little to resist save surrender itself to a bigger master.

Remember that the same history is being enacted at Jupiter and co., so that they are inundated by a plethora of gasses: their own as well as the lot just stolen! Now these planets have gasses they can call their own! To the extent that billions of years later boys and girls on a small blue-green planet will employ everything in their power to defend the thieves of yore!

More about Jupiter in the last issue of the leviathan of the Solar System.

The writer is a professional astronomer and a former head of PIA Planetarium. He can be reached at

astronomerpreone@hotmail.com