New research on the TRAPPIST-1 system shows that the seven-planet system is between 5.4 and 9.8 billion years old, suggesting that it could be over twice as old as our Solar System. The age of the system is very important to understanding its habitability, as this a strong indication to the amount of radiation being released from its star. It can also tell us about the past, as it could reveal how much radiation it has already endured.
When the system was first announced in February 2017, scientists believed the system was at least 500 million years old. As this is the time taken for stars of such low mass – in this case, eight per cent the mass of the Sun – to contract to its current size. However there was not a known upper limit, as in theory, the system could be as old as the universe, which is 13.7 billion years old. So by understanding the age of this system, the conditions on the seven planets become clearer and more intriguing.
“Our results really help constrain the evolution of the TRAPPIST-1 system, because it has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago,” says Adam Burgasser, an astronomer at the University of California, San Diego. Burgasser teamed up with Eric Mamajek, the deputy program scientist for NASA’s Exoplanet Exploration Program based at NASA’s Jet Propulsion Laboratory (JPL), California, United States, to calculate TRAPPIST-1’s age.
There are many factors to take into account when considering how a star’s radiation affects a planet’s habitability. For instead, Burgasser and Mamajek confirmed that TRAPPIST-1’s radiation is relatively quiet compared to other ultra-cool dwarf stars. When you also include its old age, its radiation was most likely much less intense then it’s early years. But still, the planets sit extremely close to the star, which would mean the seven Earth-sized planets have been absorbing high-energy radiation for several billions of years. This could strip away the atmosphere and evaporate the liquid water, causing a similar environment to Mars.
On the contrary, the radiation is not as intense, and also the densities of TRAPPIST-1’s planets are lower than Earth. This could lead to the complex molecules within the planet evaporating into a thick atmosphere, which could trap large amounts of heat, creating a harsh environment comparable to Venus. As Burgasser explains, “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.”
In terms of lifespan, the TRAPPIST-1 star could stick around for a long time. In fact, it could last longer than then current age of the universe, which is 13.7 billion years old. The life of a Sun-sized star is roughly 10 billion years, larger stars have shorter lives because they tend to use their fuel faster than dwarf stars. “Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae,” Mamajek says. “But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe.”
The TRAPPIST-1 system is becoming a clearer picture with each set of research results. Future observations with NASA’s Hubble Space Telescope and James Webb Space Telescope will analyse the atmospheres of the planets, and how similar they are to Earth’s.
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