Astronomers confirm orbital details of TRAPPIST-1’s least understood planet

Scientists using NASA’s Kepler Space Telescope have identified a regular pattern in the orbits of the planets in the TRAPPIST-1 system that confirmed suspected details about the orbit of its outermost and least understood planet, TRAPPIST-1h.

An international team of astronomers, including a postdoctoral research associate at the University of Central Lancashire (UCLan), used data gathered by the Kepler Space Telescope to observe and confirm details of the seventh exoplanet orbiting the star TRAPPIST-1.

They confirmed that the planet, TRAPPIST-1h, orbits its star every 18.77 days, is linked in its orbital path to its siblings and is frigidly cold. Far from its host star, the planet is likely uninhabitable — but it may not always have been so.

This most recent research follows news in February when scientists announced that the system has seven Earth-sized planets. NASA’s Spitzer Space Telescope, the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) in Chile and other ground-based telescopes were used to detect and characterize the planets. But the collaboration only had an estimate for the period of TRAPPIST-1h.

TRAPPIST-1 is only eight percent the mass of our sun, making it a cooler and less luminous star. It’s home to seven Earth-size planets, three of which orbit in their star’s habitable zone—the range of distances from a star where liquid water could pool on the surface of a rocky planet. The system is located about 40 light-years away in the constellation of Aquarius and is estimated to be between three billion and eight billion years old.

This most recent TRAPPIST-1 research has been announced in a paper published in the journal Nature Astronomy. Dr Daniel Holdsworth, a postdoctoral research associate at UCLan‘s Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, is one of the European scientists involved in the project and helped to determine the rotation period of the star, through the analysis of spots on the stellar surface.

He said: “We have analysed 79 days of near-continuous data of the TRAPPIST-1 system obtained with the Kepler Space Telescope in its repurposed K2 configuration. The new data allowed us to measure the orbit of the outermost planet, TRAPPIST-1 h. We have determined the orbital period to be 18.77 days, which was exactly the period the team predicted. We also found the planet to be a little smaller than Earth, with an average temperature of -100ºC.

“Furthermore, we find that all the planets form a complex chain of orbital resonances, meaning they interact with each other, effectively pulling and pushing on each other as they pass. TRAPPIST-1 is now the record for the number of planets that are interacting like this, with the previous record being four planets. This is important for the formation theory of the system as these interactions were probably present during the early stages of the system. Once the planets are in this resonant chain, it is hard to escape, and so they probably all migrated towards their host star at the same time, and remained in this intricate dance.”

“The K2 data also allowed us to measure the rotation period and activity of the star, results of which can be used to tell us how old the star is. We found the rotation period to be about 3.3 days which means the star is middle-aged, between three and eight Gyr old, or three to eight billion years old.”

The research was funded by the NASA Astrobiology Institute via the UW-based Virtual Planetary Laboratory as well as a National Science Foundation Graduate Student Research Fellowship, the Swiss National Science Foundation, the European Research Council and the UK Science and Technology Facilities Council, among other agencies.

Read the full NASA press release –

View the paper –

Featured Image: Artists impression of the system TRAPPIST-1 belongs to.