TRAPPIST-1: Scientists Learn About Planet H and the 7 Planets' Perfect Harmony

Scientists from the University of Washington (UW) used data from the Kepler Space Telescope to uncover more details about the seven exoplanets of the star TRAPPIST-1, particularly the outermost and least-known one of the bunch: TRAPPIST-1h. The new study also identified the orbital resonance of the innermost planets, revealing the harmonious relationship that keeps the planetary system stable.

The mysterious planet h

Planet TRAPPIST-1h - or planet h - is located in the outermost edge of the system and is thus the least understood of the seven Earth-sized planets orbiting the star, according to a report from the University of Washington. Now, the team led by UW's Rodrigo Luger was able to reveal a few key details about the uninhabitable planet such as its orbit around the star every 18.77 days.

Distant from its host star, planet h is an extermely cold region with an average temperature of 173 Kelvin (minus 148 F). The low temperature makes it highly unlikely to host life, although the researchers suggested that it likely spent several hundred million years as a warmer planet when the TRAPPIST-1 star was younger and brighter.

"We could therefore be looking at a planet that was once habitable and has since frozen over, which is amazing to contemplate and great for follow-up studies," Luger said.

Exoplanets' harmony in orbit

The scientists also observed the orbits of all seven TRAPPIST-1 planets, discovering that they're all locked in a complex dance in complete harmony. This is known as orbital resonance, a state where all of the planets' orbits are mathematically related with their gravitational pull tugging on each other and keeping them on course.

"All of this indicates that these orbital relationships were forged early in the life of the TRAPPIST-1 system, during the planet formation process," Luger explained in a statement from NASA. "The resonant structure is no coincidence, and points to an interesting dynamical history in which the planets likely migrated inward in lock-step."

The study was published in the journal Nature Astronomy.