Kepler’s K2 Mission Spies Details of Exoplanet TRAPPIST-1h

TRAPPIST-1h is shown as covered in ice, similar to Jupiter’s icy moon Europa. Image credit: NASA.

TRAPPIST-1, an ultracool middle-aged dwarf star found in the constellation of Aquarius, which lies at 38.8 light-years from Earth. This relatively small size and low luminosity star was the focus of the scientific community in February 2017 when astronomers announced that the star hosts at least seven planets, TRAPPIST-1b, c, d, e, f, g and h.

All of seven exoplanets orbiting the star TRAPPIST-1 are similar in size to Earth and Venus, or slightly smaller, and have very short orbital periods. Their orbits are not much larger than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System.

The star is much less luminous than the sun and it is only a bit larger than the planet Jupiter with just 8% of our Sun’s mass, this dimmed world is name after the ground-based Transiting Planets and Planetesimals Small Telescope (TRAPPIST), the facility that first found evidence of planets around it back in 2015. 

Now, an international team of astronomers, led by Rodrigo Luger, a doctoral student at the University of Washington, Seattle, lead author on a paper published on May 22 in the journal Nature Astronomy, who has confirmed that the outermost planet, TRAPPIST-1h, orbits its host star every 18.77 days, and is linked in its orbital path to its siblings and is frigidly cold. This world is far from it parent star and is likely uninhabitable, but it may not always have been so.

The TRAPPIST-1 system contains a total of seven Earth-size planets. Three of them — TRAPPIST-1e, f and g — dwell in their star’s so-called ‘habitable zone.’ Image credit: NASA.

The TRAPPIST survey is led by Michael Gillon of the University of Liège, Belgium, who is also a coauthor on this research. The astronomers studied the TRAPPIST-1 system in greater detail using 79 days of observation data from K2 and they were able to observe and study four transits of TRAPPIST-1h across its star, discovering that TRAPPIST-1’s planets appear linked in a complex dance known as an orbital resonance, where their respective orbital periods are mathematically related and slightly influence each other.

“Resonances can be tricky to understand, especially between three bodies. But there are simpler cases that are easier to explain,” Luger said. For instance, closer to home, Jupiter’s moons Io, Europa and Ganymede are set in a 1:2:4 resonance, meaning that Europa’s orbital period is exactly twice that of Io, and Ganymede’s is exactly twice that of Europa. TRAPPIST-1’s seven-planet chain of resonances established a record among known planetary systems, the previous holders being the systems Kepler-80 and Kepler-223, each with four resonant planets.

“These orbital connections were forged early in the life of the TRAPPIST-1 system, when the planets and their orbits were not fully formed,” Luger said. “The resonant structure is no coincidence, and points to an interesting dynamical history in which the planets likely migrated inward in lock-step. This makes the system a great testbed for planet formation and migration theories.”

Sources: NASA, Wikipedia, sci-news, University of Washington,