You have to imagine Jupiter as a big brute of a thing. This is not difficult. Jupiter is a big brute of a thing.

It is 300 times the mass of the Earth and plays tug of war with the Sun over the gravitational dominance for the Solar System.

The Sun wins, of course, but Jupiter is a big brute of a thing, remember, and doesn’t take second place lightly. The big brutish Jupiter had been, in scientists’ minds, locked in its orbit since the formation of the solar system four billion years ago, like a clockwork orrery.

But such an inflexible approach yielded four mysteries, spelt out by Dr Marek Kukula at Greenwich’s Royal Observatory as part of Horizon’s Secrets Of The Solar System.

  1. Venus and the Earth are about the same size. Mars, the other bit of near-sun rocky debris, is only the tenth of their size. How come?
  2. Uranus and Neptune are way too far out than models predict.
  3. The rocky and icy asteroid belts formed under very different circumstances but ended up in the same place. How come?
  4. The moon is a pock-marked bulls-eye, apparently the victim of excessive bombardment

The answer to these mysteries was partially revealed in the search for planets in other stellar systems.

The first was spotted in 1995 and since then all sorts of weird contortions of planets and orbits and stars have been yielded up by ever better telescopes.

At that stage “planet migration” became a thing among astronomers. Jupiter could not form close to the Sun, which would nick its raw materials. Yet so-called Hot Jupiters whizz around their stars plainly having found themselves there by the pinballing of violent migration.

Turns out – spoiler alert – that our Jupiter, too, was spiralling in towards the Sun but was held in check by Saturn. The net result was that it (a) hoovered up planet material (Answer 1) (b) Flung other planets and materials hither and thither (Answer 2 & 3 ) and (c) generally caused agitation and bother in the Solar System (answer 4).

One scientist even suggested that another ice giant was flung out of the solar system altogether, destined to wander the Universe like a huge Oliver Twist looking for home, warmth and acceptance.

Anyway, much of these ideas will have some solid basis when Juno ends its five-year mission to reach Jupiter and discover whether its core is rocky or whether it’s gas all the way down. Providing it shows respect to the grand old pinball wizard.

Secrets Of The Solar System is available on iPlayer