Our solar system follows a definite pattern, with small rocky planets close to the sun and large gaseous planets farther away. On a macro level, such a pattern seems to make sense.

At the beginning of the Sun's formation, the abundant energy of the new solar wind would have pushed lighter materials like hydrogen and helium into the outer layers of the solar system, leaving only rocky materials behind.

It would seem that most solar-like systems would follow the same pattern, but as humans explore more and more extrasolar galaxies, we are finding that this is not the case. Our solar system seems to be an exception. Having studied other galaxies, we have found that gaseous planets far from their stars are very rare. In our solar system, all the gaseous planets are cold, but among other confirmed extrasolar planets, the number of cold planets does not exceed 20 percent.

With computer simulations, we can get a first look at why. In immature galaxies, the stuff that forms all the matter of future star systems comes from protoplanetary disks, which are composed of liquid gas and dust. Since the gas is usually ionized, it interacts with the magnetic field of the central star. Turbulence can form in the protoplanetary disk due to the collision and collection of dust.

Physically, being able to describe this system in terms of magnetohydrodynamics, the calculations are difficult to describe, but with modern supercomputers, we can spot some general trends. Low-mass planets do not strongly disturb the general structure of the protoplanetary disk. Their interaction within the protoplanetary disk induces the formation of spiral density waves.

Since the pull of the outer spiral is greater than that of the inner spiral, the planet moves closer to the star, which is called Type Ⅰ migration. High-mass planets (more than 10 times the mass of the Earth, or just below the masses of Uranus and Neptune) not only induce density waves but also create openings in the protoplanetary disk. This means that although the internal pull is still there, it becomes smaller, so the planet moves closer to the star as it forms, which is called Type II migration. Both types of migration bring the planet closer to the star, so hotter planets are more common.

So why did Jupiter form so far from the Sun?

It has long been hypothesized by the Great Voyage model that Jupiter had roamed toward the inner solar system and then back to the outer reaches, and at one point it moved close to where Mars is today. The planet's movement had a profound effect on the solar system, changing the nature of the asteroid belt and making Mars smaller than it should be.

The universe is vast, there are 300 billion stars in the Milky Way and 300 billion possibilities for life to exist, and there may be habitable Earths like Earth, but the vast majority of planetary systems will not be like our home system, the Solar System.