The ultra-cool dwarf star of the intriguing TRAPPIST-1 planetary system is up to twice as old as our solar system, a study has found. TRAPPIST-1 is a system of seven Earth-size planets orbiting an ultra-cool dwarf star about 40 light-years away.
In a new study, researchers found that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago. At the time of its discovery earlier this year,scientists believed the TRAPPIST-1 system had to be at least 500 million years old. “Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years,” said Adam Burgasser, an astronomer at the University of California, San Diego in the US.
“This means the planets had to evolve together, otherwise the system would have fallen apart long ago,” said Burgasser, first author of the research published in The Astrophysical Journal. It is unclear what this older age means for the planets’ habitability. On the one hand, older stars flare less than younger stars, and researchers confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water, researchers said.
The equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h, they said. However, old age does not necessarily mean that a planet’s atmosphere has been eroded, said Eric Mamajek, deputy programme scientist for NASA’s Exoplanet Exploration Programme. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation.
A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate, researchers said. “If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years,” Burgasser added.