The TRAPPIST-1 Planets Are Older Than Earth

Artist's impression of some of the TRAPPIST-1 planets. ESO/M. Kornmesser/N. Risinger (skysurvey.org)

American astronomers have estimated the age of the seven-exoplanet system, TRAPPIST-1, and it turns out that it’s older than the Solar System. Using different types of estimators, researchers from NASA and the University of California San Diego claim that the system could almost be twice as old as ours.

The study, accepted for publication in the Astrophysical Journal, focuses on eight different properties of the star, such as rotation, magnetism, color, and composition. This allowed the researchers to claim that the system is likely as young as 5.4 billion years or as old as 9.8 billion years. The range of correct ages is obviously large, but this estimate is already revealing a lot about the system.

"Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years," first author Adam Burgasser, from the University of California San Diego, said in a statement. "This means the planets had to evolve together, otherwise the system would have fallen apart long ago."

The TRAPPIST-1 system is made of seven Earth-size exoplanets, each orbiting their tiny red dwarf star in a matter of days. But their orbits are not at random. They are synchronized in a so-called orbital resonance, so their periods are all in proportion with one another. They are also so close to their star that they are tidally locked, so one face is always in starlight, while the other is in perpetual darkness.

This latest estimate complicates the issue of “potential life” on these planets. Three of the seven planets are in the star's habitable zone, which makes it great for life. But red dwarfs, although dimmer stars like the Sun, are very active, releasing stellar flares and high-energy radiation. That is obviously pretty bad. The research tells us that the system is extremely stable to survive billions of years and that older red dwarfs are usually less active than younger red dwarfs. Yet could an atmosphere have survived for so long after being bombarded by radiation?

These are just a few of the complex notions we need to take into account to estimate their true habitability. Life on these planets appears to be unlikely, but no one can yet say for certain. And that’s what makes it interesting.

"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.

Ultra-cool red dwarfs like TRAPPIST-1 are very slow burners, and will continue to shine for 900 times longer than the current age of the universe.

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