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Exploring the Worlds of TRAPPIST-1

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TRAPPIST-1 System. Credit NASA.

In 2016, Belgian scientists first discovered TRAPPIST-1, a planetary system composed of a star orbited by seven Earth-sized rocky exoplanets (planets outside of our solar system). TRAPPIST-1 is located 40 light years away from our solar system and is the most studied planetary system other than our own. Now, the race is on to uncover the mysteries of the TRAPPIST-1 exoplanets. Do they contain water? Do they have atmospheres? Is there a possibility of life out there?

AU’s Thomas Fauchez, a research assistant professor in the Department of Physics and a space scientist at NASA Goddard Space Flight Center, is part of an international collaboration of scientists that works on sophisticated computer models to help answer these questions. We asked Fauchez to explain his groundbreaking work and the importance of TRAPPIST-1 as scientists search for signs of life and learn more about our own solar system and how our planets compare with its exoplanets.

Q: Key to your research is the use of earth science and climate models to study the environments of TRAPPIST-1. How are these models applicable to studying TRAPPIST-1?

We use multi-model comparisons to improve how we predict and interpret telescope observations of exoplanets. Global climate models are used by many climate scientists around the world to predict the past, present and future of Earth’s climate. They are extremely complex because they attempt to simulate and connect together all known surface and atmospheric phenomena of Earth. They are, for instance, used to predict current and future climate change. They were first developed to understand Earth, but exoplanets, specifically the rocky, Earth-like ones orbiting the TRAPPIST-1 star, can also benefit from the use of such models. We are using the earth science and climate models to make predictions about what the exoplanets’ potential climate may look like under certain atmospheric compositions. This is how we, exoplanet climate scientists, study exoplanet habitability.

All seven planets discovered in orbit around the red dwarf star TRAPPIST-1 could easily fit inside the orbit of Mercury, the innermost planet of our solar system. Credit: NASA.

Q: You have a particular focus on the exoplanet TRAPPIST-1e. Can you explain the significance of this exoplanet?  

A: The exoplanet TRAPPIST-1e is the fourth out of seven exoplanets orbiting a tiny red dwarf star in the TRAPPIST-1 star system. Crucially, the planet’s orbit lies within the habitable zone of TRAPPIST-1 and so may have a temperate climate suitable for liquid water to exist on its surface.

Q: While there’s much excitement around the James Webb Space Telescope for the amazing images of space, its mission encompasses what it will be able to tell us about the worlds beyond our own. Can you talk about how the James Webb Space Telescope will be used to gain insights into TRAPPIST-1? How does this intersect with your models?

We have yet to detect an atmosphere on any of the TRAPPIST-1 exoplanets. We are expecting the James Webb Space Telescope to make such a finding. The J.W.S.T. and others such as the European Extremely Large Telescope, the Thirty Meter Telescope or the Giant Magellan Telescope may soon be able to characterize, through transmission, emission or reflection spectroscopy, the atmospheres of rocky exoplanets orbiting nearby red dwarf stars. As our work shows, modelling goes hand in hand with the observations of telescopes. The modelling of exoplanet atmospheres is an essential step prior to telescope observation.

The exoplanet TRAPPIST-1e with a modern Earth-like atmosphere as modeled by four global climate models. Credit: Jay Friedlander and Britt Griswold, NASA Goddard Space Flight Center

Q: Your team has published three new research papers in Planetary Science Journal. What were the findings?

Overall, the aim of our project is to refine our models, tweak them as necessary, and to make sure they roughly agree before using them to interpret data from telescope observations. Our new findings concern the exoplanet TRAPPIST-1e.

We showed for the first time how the use of a specific global climate model will be able to impact data interpretation and planning of telescope observational campaigns. In short, the team found that the four exoplanet climate models we were comparing predicted similar climate, but with some notable differences, mostly attributed to discrepancies in the amount and altitude of clouds. We simulated the transmission spectroscopy as seen by J.W.S.T., which is how the telescope observes light from the star crossing the exoplanet’s atmosphere and the number of transits the telescope must observe to detect an atmospheric signal. This light is modified by the presence of gas in the exoplanet’s atmosphere that creates a transmission spectrum.

When comparing our models, we found that differences about clouds and water vapor led to a wide margin of error of 50 percent variation in the predicted observation time that would be needed to detect such an atmosphere with the telescope. It is the first time that such uncertainty has been estimated. The data can help scientists determine the appropriate number of transits the telescope would need to make. 

Furthermore, the team believes that our international collaboration will not only pave the way for robust modelling of potentially habitable distant worlds, but we are also connecting our efforts to find life beyond Earth with studies of our own changing climate.

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