Mini Alien Star System is a Clockwork Wonder
The compact star system maintains its intricate balance through orbital resonance.
When NASA's Kepler space telescope detected the "mini-solar system" of Kepler-80 in 2012, astronomers were astonished by how crowded it was. There are five worlds all orbiting their star well within the distance Mercury orbits the sun.
The discovery of Kepler-80 -- and other compact star systems like it known as Systems with Tightly-spaced Inner Planets, or "STIPs" -- challenges our understanding of how planets form, even adding an extra perspective to how Earth may have evolved.
Now astronomers have taken a long, hard look at Kepler-80, which is located around 1,100 light-years away, and are beginning to understand what makes it tick.
One of the biggest questions challenging our understanding of this system is how could all the exoplanets maintain their apparently stable orbits in such a small region? Wouldn't their motions have been thrown into dynamical chaos long ago?
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Each exoplanet has an orbital period (or "year") of just one, three, four, seven and nine days. Whipping around the star at such high speed and close proximity should pose a problem; their gravities should interfere with one another.
And in new research to be published in the Astrophysical Journal, they do affect one another, but not in the negative sense. Researchers were able to precisely measure the orbital periods of all the planets and detected very slight gravitational tugs as they passed one another. The technique is known as transit timing variations and it has been used by Kepler before to detect the gravitational tug of worlds that remained undetected.
These precise measurements led the researchers to discover that all five worlds are in a tight, synchronized dance that maintains the stability of the whole star system.
"The outer four planets return to almost exactly the same configuration every 27 days," said Darin Ragozzine, of Florida Institute of Technology, in a statement.
This synchronicity is known as orbital resonance. As Kepler-80 formed, the tight orbits of the planets it contained evolved into a clockwork-like balance, ensuring their orbits remained stable.
The four outer exoplanets are thought to be of between four to six times the mass of Earth and the two outermost worlds have diameters that are twice as large as the inner worlds. It is therefore thought the two outer worlds are gas giants.
After carrying out computer simulations of the evolution of Kepler-80, the researchers think all the worlds formed in much wider orbits, eventually migrating closer to the star. Over time, their orbits started to synchronize and settled into this uniquely compact state.