This guest post was written by Payal Shah, an undergraduate student at the University of Connecticut, for an assignment in the Fall 2019 Foundations of Modern Astrophysics class taught by Professor Cara Battersby. Payal is a Computer Science major and is double minoring in Astrophysics and Math. Payal’s biggest aspiration, besides getting a dog, is to find life. When not dreaming about that or caught up in schoolwork, you can find Payal playing volleyball, watching Avatar: the Last Airbender, or playing RPGs.
Orange hues of sunset dousing every mountain and valley as celestial bodies from the same solar system rise unbelievably huge in the sky — life on a TRAPPIST-1 planet wouldn’t be too far off from this. Discovered in 1999, TRAPPIST-1 was originally called 2Mass J23062928-0502285 since it was uncovered using the Two Micron All-Sky Survey, or 2Mass for short. Later, in May 2016, scientists located three planets orbiting the star using transit photometry with the TRANsiting Planets and Planetesimals Small Telescope or TRAPPIST. This led to the 2017 discovery of four more exoplanets orbiting the host star with the Spitzer Space Telescope and the – I kid not – Very Large Telescope at Paranal among a few more. TRAPPIST-1, an ultra-cool red dwarf star, is only slightly larger than our very own Jupiter, yet much more massive. It is located in the constellation Aquarius and is about 39.6 lightyears, or 12.1 parsecs for the more scientific souls, away from the Sun. TRAPPIST-1 is also much older than our 4.6 billion year old Sun at 5-10 billion years and is about 8% of its mass.
There are seven terrestrial planets orbiting the star — this is the largest amount in a solar system found to date! All the planets in the system except TRAPPIST-1c have densities low enough to indicate the presence of water in any state. TRAPPIST-1b and c are also unlikely to have the hydrogen-dominated atmospheres typical of usual gas giants. Such an atmosphere increases the likelihood of a planet with rocky terrain and water. TRAPPIST-1b and c experience heating from planetary tides to keep magma oceans in the rock mantles and TRAPPIST-1c may have volcanoes with silica magma on its surface. Six of the planets take anywhere from 1.5 days to 12.4 days to orbit their sun and the farthest planet, TRAPPIST-1h, orbits the host star every 19 days, which makes for insanely short years. In contrast, night and day on the planets seem eternal. The planets are all tidally locked so only one side of the planets permanently faces its sun, much like our moon. We only see one side of the moon since it is tidally locked with the Earth. This makes the development of life much more unlikely since one side is always lit and the other is always dark, but if the atmospheres of these planets were able to dissipate heat across their surfaces, life could still thrive. Up to six of the planets may have had a chance to be in the optimal habitable zone but three are observed to definitely be in this zone. These planets are TRAPPIST-1e, d, and f. From what scientists know, TRAPPIST-1e is the most likely to be habitable. It has the most Earth-like ocean world and would be an excellent choice for further study with habitability in mind.
The sad news for all anti-Earth fanatics is that K2 observations with Kepler revealed that several flares shoot off from the host star of the TRAPPIST system. This means unless there’s some way of avoiding this scalding hot ouch, living in TRAPPIST-1 is a no-go. The inner planets in TRAPPIST-1 may have lost a large amount of water due to this, but the outermost ones have likely retained most of theirs. Planets in the TRAPPIST-1 system orbit much closer to their host star than Earth does to the Sun, hence the short years, which puts the planets in danger of magnetic flares that are 10 to 10,000 times stronger than the most powerful geomagnetic storms Earth has seen. That is insanely dangerous because, aside from the awful radiation any sort of life would be exposed to, we would also have to worry about the planets getting their chemical composition upended. The flares occur on a regular basis and that type of exposure can permanently alter the chemical make-up of the planets and cause detrimental erosion to the atmosphere. If there was a strong enough magnetic field, the exoplanets could shield their atmosphere from the harmful effects of such eruptions but said magnetic field would have to be 10 to 10,000 Gauss to protect from the flares. For comparison, the Earth’s magnetic field is around 0.5 Gauss. That’s a lot of Gauss!
Ideally, if life were to exist on TRAPPIST-1, any possible life through abiogenesis (the process by which life emerges) on the planets would spread to the others in the system through panspermia, the transfer of life from one planet to another via space dust, asteroids, comets, etc. More specifically, abiogenesis describes how abiotic objects became living organisms, such as simple organic compounds, through natural processes. Panspermia is all the more likely when you consider that planets in the habitable zone have a separation of less than 0.01 AU from each other. The likelihood of interplanetary panspermia in TRAPPIST-1 is about 10,000 times higher than the likelihood of panspermia from Earth to Mars.
As for possible existing intelligent life on the planets, Astronomer Seth Shostak from SETI Institute has searched through 10 billion radio channels with his peers in search of signals from TRAPPIST-1 but unfortunately, no transmissions were detected. Further observations with the more sensitive Green Bank Telescope resulted in similar conclusions.
On that rather hopeless note, there’s still much more astrophysicists can learn from TRAPPIST-1. Now that we know a red dwarf can support a planetary system that will remain stable for over a billion years with multiple terrestrial planets orbiting it, we can safely assume that there may be other such systems and, fortunately, there are a multitude of red dwarfs in the universe for us to search around. This search will inevitably lead us to more planetary systems, many of which will likely turn out to be absent of life. However, they could be candidates for our next home if Earth is no longer an option — or a destination for a very exciting vacation!