The first confirmed detection of an exoplanet came in 1992, followed by the first detection of an exoplanet orbiting a star in 1995. Improved observational techniques have since seen the rate of discoveries accelerate and up until now astronomers have uncovered 692 planetary systems and 884 planets outside of our own solar system.
With a multitude of other planetary systems to study, perhaps the biggest surprise to scientists is how very few resemble our own solar system. In fact, far from being ordinary as astronomers first suspected, so far only one planetary system (HD 13931 b) has been detected which resembles our own.
One major concept that now needs to be rethought since studying these multiple planetary systems is our understanding of frost lines, or a particular distance away from a sun beyond which it gets too cold for rocky planets to form. As the theory goes, when a planetary system is forming the dust inside the frost line melts eventually forming rocky planets like the Earth and Mars. Further out past the frosty side, however, the dust stays gassy accounting for gas giant planets such as Jupiter, Saturn and Neptune.
As astronomer Mike Brwn from Caltech, explains: “Before we ever discovered any [planets outside the solar system] we thought we understood the formation of planetary systems pretty deeply. It was a really beautiful theory. And, clearly, thoroughly wrong.”
In addition, unlike Earth’s solar system in which the innermost planet Mercury revolves around the Sun in 88 days, rocky exoplanets have been discovered with orbits lasting as little as 3.7 days. So far the evidence is beginning to suggest our solar system is far from ordinary, and may even be a bit of a freak compared to the norm. As University of California astronomer Steve Vogt, comments:
“We are now beginning to understand that nature seems to overwhelmingly prefer [planetary] systems that have multiple planets with orbits of less than 100 days..So our solar system is, in some sense, a bit of a freak and not the most typical kind of system that Nature cooks up.”