A long, long time ago, in a galactic nebula not too far away, our sun and solar system was born from a swirling cloud of elements - molecular hydrogen, helium, carbon, molecular oxygen, iron and a smattering of others.
The standard model for this process - the core-accretion theory - was one of the simplest and most elegant theories in astronomy. It relied of only a few basic physic and chemistry principles driven predominantly by gravity.
It explained why all of the planets orbit the sun in the same direction as the sun itself spins. It explained why the orbits of the planets are close to circular and in or near the plane defined by the sun's equator.
It also accounted for why the inner planets are rocky with iron cores and why the outer four planets are gas giants composed of hydrogen and helium. It was a theory that seemed to explain the solar system perfectly.
Indeed, it was such an elegant and simplistic theory that astronomers assumed that it would apply to all of the solar systems in the universe. Unfortunately, that is not the case.
In the mid-1990s, astronomers discovered the first exo-planet orbiting a nearby star. Since then the number of planets discovered about other stars has multiplied into the thousands. Astronomers now have enough planetary systems that they can do statistical analyses. It turns out that our solar system is not so common or typical.
For example, the most common type of exo-planet is a super-Earth somewhere in size between our planet and Neptune, not found in our neighbourhood. Gas giants have been found orbiting their stars at distances closer than Mercury.
Planetary systems have been observed with planets orbiting in the opposite direction to the spin of their Suns or whipping around their Suns in highly elliptical orbits. Some exo-planets have even been detected in polar orbits.
All of this has forced scientists to reconsider how solar systems might form. Most astronomers agree that the core-accretion theory has some things going for it. Planets are the leftovers from the formation of stars. They are generated from the heavier elements.
It is possible that eccentric orbits result from the interaction of planets formed in very close orbits. It has also been postulated that the large planets in tight orbits might have arrived close to their stars through orbital decay. But a comprehensive theory has yet to be developed.
However, more recent research on our solar system might offer up additional data for consideration. It turns out that our solar system might be a little older than previously thought.
The age of the Solar System can be estimated by looking at the ratio of isotopes of certain elements. The first estimates came from considering the ratio between lead-207 and lead-206. Both isotopes are generated as the end product of radioactive decay but by different pathways. Consideration of their relative abundance can be used to date the rock that they are found in.
In the case of meteorites or extra rocks leftover from the very formation of the planets, the ratio of isotopes gives us the age of the solar system. But lead is not the only element or isotope that can be used for determining age.
Examining the ratio of aluminum to magnesium allows scientists to examine smaller time scales. Recent research has resulted in is a revision of the age of the solar system by about 1 million years. Given that it is about 4.568 billion years old, a million years here or there shouldn't be a big deal.
But the difference is enough to suggest that the solar system was born in a cloud of dust and gas similar to that seen in the Orion Nebula. Within the cloud, giant stars burned hot. They produced huge amounts of high energy ultraviolet light. These photons applied pressure to the surrounding media.
As a result, these giant stars existed within a slowly expanding bubble of gas expanding outward to carve out a cavity. As the cavity expanded, it pushed the gas and dust ahead of it and into the expanding gas and dust spheres of other gas giants. This resulted in an increased density in the surrounding cloud leading to increased gravitational pull and initiating the collapse of the cloud into our solar system.
This model suggests that if this is a common mechanism for solar system formation, the resulting planetary structure would be influenced by the surrounding stars. Gravitational attraction by giant stars could easily distort the orbit of any planets formed. Further, it would help to explain the richness of elements such as iron, nickel, and copper within our solar system.
The best part is that everything around us would be made from star dust generated billions of years ago. We are stardust, we are golden.
