In the constellation of Cygnus, 1,100 light-years from Earth, there’s a curious planetary system with five small planets orbiting all very close to their star Kepler-80. The system was discovered in 2012, but only now are astronomers able to confirm the exact dynamics of the system.
Undergraduate student Mariah MacDonald from the Florida Institute of Technology, together with her Professor Darin Ragozzine and collaborators from other universities, discovered that the four outermost planets have masses between four and six times that of Earth, with two of them being much wider due to puffy atmospheres.
This star system is known as a STIP (system with tightly-packed inner planets), and researchers are interested in STIPs because they can help us understand how planets, even in our own Solar System, reach their present-day orbit. The findings have been accepted for publication in the Astrophysical Journal, and are available online.
The planets most likely formed further away from the star, and at a later time moved from these outer orbits in a process called planetary migration. The migration had a secondary but important effect: It synchronized the rotational period. The planets are now said to be in resonance.
The five planets orbit Kepler-80 about every one, three, four, seven, and nine days. The resonance helps the system to remain gravitationally stable, and it has been observed in the moons of Jupiter as well as other exoplanets.
"The outer four planets return to almost exactly the same configuration every 27 days," said Ragozzine in a statement.
By using simulations, the team was able to show that resonance actually arises naturally from planetary migration. The entire system is within 12 million kilometers (7.3 million miles) from the star, less than 8 percent the distance between Earth and the Sun.
NASA’s Kepler observatory has discovered hundreds of other STIPs that have between three and seven members that take between one and 100 days to orbits their stars. This novel understanding of Kepler-80 will hopefully spearhead more investigations of STIPs and tell us something new on how planets form.