A star system discovered by the Kepler Space Telescope has five planets packed into tight orbits in an unusual configuration known as a resonance.
Kepler-80, located 1,100 light years from Earth, is orbited by five small planets all orbiting in an area 150 times smaller than Earth’s orbit around our Sun.
The planets orbit so close to the star and to each other that Kepler was able to determine each one’s orbital period by their gravitational influences on one another.
Their “years” are one, three, four, seven, and nine Earth days.
Undergraduate Mariah MacDonald and assistant professor of physics and space sciences Darrin Ragozzine, both of Florida Institute of Technology, studied the planets and their strange orbital configuration.
Along with 11 co-authors, they are publishing their findings in the Astronomical Journal.
The researchers measured the four outer planets as having masses four to six times that of Earth. But while all four have similar masses, the two outermost planets are twice as large, likely due to their having thick atmospheres of hydrogen and helium.
It is unusual for scientists to be able to obtain such detailed estimates of the composition of multiple planets in a single system.
Kepler-80 is one of hundreds of Systems with Tightly-spaced Inner Planets or STIPs discovered to date. These systems typically are composed of three to seven small planets, all of which orbit their star in 100 days or less.
Even more strangely, Kepler-80’s four outer planets have synchronized or resonant orbits that keep the whole system gravitationally stable.
“The outer four planets return to almost exactly the same configuration every 27 days,” Ragozzine noted.
This arrangement likely occurred through a process of planetary migration, in which the planets moved closer to the star while still forming.
In computer simulations, such migration resulted in planets entering synchronized orbits much like those of Kepler-80.
Studying STIPs is providing scientists with new insights into planetary formation processes and could even yield new understanding of Earth’s origin.