Our solar system is the rarest kind of four types of planetary system, suggests new research
To us everything seems normal. Our planet, blue and bursting with life, sits in the middle of the “habitable zone” around the Sun, with burning hot Venus inwards and lifeless Mars beyond. Giant gas planets exist way farther out.
That’s as how it should be, right? Not at all. Two new studies published (here and here) in the scientific journal Astronomy & Astrophysics reveal that our solar system is, in fact, in a class of its own.
Exoplanetary systems are a puzzle to astronomers. Data from the Kepler Space Telescope—the discoverer of the first big tranche of exoplanets—found that in many planetary systems the planets tend to resemble their neighbors. For example, if there are three planets orbiting a star then they all tend to be a similar size and mass.
However, Kepler’s data was limited. “It was not possible to determine whether the planets in any individual system were similar enough to fall into the class of the ‘peas in a pod’ systems, or whether they were rather different—just like in our solar system,” said study lead author Lokesh Mishra, researcher at the University of Bern and Geneva and NCCR PlanetS.
Artist impression of the four classes of planetary system architecture.
Combing through the data the researchers actually chanced upon four classes of star systems:
- Similar: the masses of neighbouring planets are similar to each other. About eight out of ten planetary systems around stars visible in the night sky have a this architecture.
- Ordered: the mass of the planets tends to increase with distance from the star—just as in our solar system. This is the rarest class.
- Anti-ordered: the mass of the planets roughly decreases with distance from the star.
- Mixed: the planetary masses in a system vary greatly from planet to planet.
A new architecture framework allows researchers to study an entire planetary system at the systems ... [+]
How and why planetary systems have different architectures could be down to the mass of the gas and dust disk from which the planets emerge, suggests this research. “From rather small, low-mass disks and stars with few heavy elements, ‘similar’ planetary systems emerge,” said Mishra. “Large, massive disks with many heavy elements in the star give rise to more ordered and anti-ordered systems (while) mixed systems emerge from medium-sized disks.”
Although planets colliding with each other, or being ejected from their star systems, also has an impact on what a planetary system ends up looks like, the takeaway is that the end is baked-in from the beginning.
“Now, for the first time, we have a tool to study planetary systems as a whole and compare them with other systems,” said study co-author Yann Alibert, Professor of Planetary Science at the University of Bern and NCCR PlanetS. “A remarkable aspect of these results is that it links the initial conditions of planetary and stellar formation to a measurable property—the system architecture,” said Alibert. “Billions of years of evolution lie in between them [and] for the first time we have succeeded in bridging this huge temporal gap and making testable predictions.”
The solar system is rare—and we could soon find out why.
Wishing you clear skies and wide eyes.
