Complex Origins Of Solar Systems
July 25, 2013

Researchers Shed Light On Solar Systems’ Complex Beginnings

John P. Millis, PhD for - Your Universe Online

Centuries ago, as astronomers began to discover the extent of our solar system, they also began to develop theories on how our Solar System was formed and how it evolved. The challenge was that the only model available was that of our own - other planetary systems would not be discovered until the later part of the 20th century - so researchers assumed that all solar systems would likely look like ours: central star, small rocky planets in the inner orbits, large gas giants farther out, nearly circular orbits, etc.

So models developed were meant to explain these characteristics. In general, lighter elements would make their way from the inner solar system out to the edges more readily, while more massive atoms would be bound up closer to the Sun. But in general, the motion of atoms throughout the solar system would be unidirectional.

In the last several decades, however, our knowledge of other solar systems has changed this view. In many cases super-Jupiters are found to orbit extremely close to their parent stars, sometimes within the orbit of our Mercury. To get a better picture of solar system formation, researchers have begun to develop methods to identify how the elements moved throughout and ultimately combined to form planets in the early solar system.

One method is to look for small crystalline particles that would have formed near the Sun, but been pushed out into the solar system to be absorbed by comets. Yet another study involves looking at traces of isotopes - an atom that has the same number of protons as a certain element, but a different number of neutrons - in the oldest meteorites.

Over time the isotopes will decay into new elements called daughter elements. The relative abundances of these isotopes will indicate where they may have originated. Analysis of Aluminum isotopes, for instance, supports the view of a one-way movement of elements through the solar system. Conversely, oxygen isotopes would indicate a more complex version of events.

Now, Alan Boss from the Carnegie Institution has published a new model in The Astrophysical Journal that suggests that gravitational instabilities in the gas disk surrounding the forming Sun could explain these results. Over time the instabilities would draw elements inward, leading to an accretion on to the proto-star. The result would be an outburst of radiation, a phenomenon observed in other proto-star systems.

Because different elements like aluminum and oxygen would enter the proto-planetary disk by different mechanisms, Boss explains that his model would then expect the different, observed patterns.

"These results not only teach us about the formation of our own solar system, but also could aid us in the search for other stars orbited by habitable planets," Boss said. "Understanding the mixing and transport processes that occur around Sun-like stars could give us clues about which of their surrounding planets might have conditions similar to our own."