Chuanfei Dong is looking to the stars to try to answer one of astronomers\u2019 most vexing questions: Are there other habitable planets in our universe?<\/strong><\/p>\n Dong<\/a>, an assistant professor of astronomy, specializes in the physics of plasma, the fourth state of matter. Our sun and other stars are composed of plasma, and Dong\u2019s knowledge of how these hot, electrically charged gasses work helps him understand the impact of stars on exoplanets\u2014planets outside our solar system\u2014and on their potential habitability.<\/p>\n Dong says surface habitability comes down to one thing: atmosphere. A planet\u2019s atmosphere needs the right balance of gasses to support the conditions for most life to thrive. \u201cFor example, on the moon and Mercury, there\u2019s practically no atmosphere. Mars\u2019 atmosphere is very thin,\u201d he says.<\/p>\n Scientists can learn a lot about the evolution of an exoplanet\u2019s atmosphere by studying the activity of nearby stars. Stellar magnetic activity, like coronal mass ejections\u2014the eruption of plasma from the stellar surface\u2014can impact the atmospheres of exoplanets over time. To predict whether an exoplanet could be habitable, Dong calculates the loss of its atmospheric gasses to space, due to stellar activity. By running numerical simulations, he\u2019s able to estimate whether any atmosphere remains. \u201cIf there\u2019s no atmosphere, then intelligent life like us cannot survive on the surface of a planet.\u201d<\/p>\n Arts <\/em>x Sciences<\/em> spoke with Dong about his research and his involvement as an institutional principal investigator on the Mauve mission, which will begin in 2025 and could provide answers to the mystery of exoplanet habitability.<\/p>\n A<\/em>xS<\/em>: Your work straddles the fields of astronomy and physics. What inspired you to pursue this research on the habitability of exoplanets?<\/strong> The Mars Atmosphere and Volatile EvolutioN<\/a> (MAVEN) spacecraft was launched by NASA to study how the Martian atmosphere escaped from an early warmer wet Mars. We know Mars had a thick atmosphere in the past, but today\u2019s Mars has almost no atmosphere. One of the primary objectives of this mission is to study the solar wind stripping, which needs plasma. So, we need to use the knowledge of plasma to study how those charged particles streaming away from the sun interact with the planetary atmosphere.<\/p>\n Most of our knowledge used to study exoplanets is based on what we learn from our solar system, because observation is highly limited for those exoplanets. Traditionally, astronomers were the ones to detect those exoplanets and characterize them, but about 10 years ago, planetary science, earth science, space physics, all the people from these disciplines, including me, jumped in together to study and characterize exoplanet habitability. I use my knowledge in space plasma physics, and I found it\u2019s very suitable to study how stellar wind and activity interact with those exoplanets.<\/p>\n How does your work studying plasma relate to the search for habitable exoplanets?<\/strong> A star, or the sun, is a plasma ball basically. In order to understand how stellar activity impacts exoplanets, we need to understand the origin of the stellar activity\u2014and that requires knowledge of plasma physics.<\/p>\n You may have heard about solar flares, or solar storms. During those events, the radiation becomes much higher, and the star releases a huge amount of mass that impacts the planets. Those flare events, or stellar storm events, can be explained by the breaking and rejoining of magnetic field lines\u2014an ubiquitous process in plasmas. With my knowledge in plasma physics, I can understand the origin of stellar activity, including flares and coronal mass ejections.<\/p>\n What does understanding the origin of the stellar activity tell you about the habitability of a planet? Are there key factors that you consider in order to make a prediction as to whether an exoplanet is habitable or not?<\/strong> Stellar wind, stellar activity, is very important in removing heavy elements like oxygen [from the atmosphere]\u2014heavy compared to hydrogen or helium. When we define habitability, especially for intelligent surface-based life, the atmosphere is one of the most important factors. For example, on the moon and Mercury, there\u2019s practically no atmosphere. Mars\u2019 atmosphere is very thin.<\/p>\n The reason I study atmospheric escape is, if I have the escape rate, I can calculate how much atmosphere will be stripped away during the process. And in most cases, we know how old a system is. If I do an integrated calculation of the escape rate over time, that is the total amount of the escaped atmosphere, then I can estimate if there\u2019s anything left or not. If there\u2019s nothing left, then there\u2019s no atmosphere. If there\u2019s no atmosphere, intelligent life like us cannot survive on a planet. The main point is, I want to link habitability to the existence of an exoplanet\u2019s atmosphere.<\/p>\n
\nDong:<\/strong> [Researching] the habitability of exoplanets is highly interdisciplinary. We need knowledge from different fields. When I did my PhD at the University of Michigan, I mainly focused on plasma physics and the solar wind interaction with Mars.<\/p>\n
\nFor my Sloan fellowship proposal last year<\/a>, that\u2019s what I was thinking about\u2014how to combine my research of plasma physics and exoplanetary science.<\/p>\n
\nAfter we understand the stellar activity, we can study how it impacts those planetary systems. I published one paper in 2018, in which I predicted that those close-in exoplanets orbiting around the Trappist-1 star [a red dwarf star with seven Earth-size exoplanets] have no atmospheres. Recently, observations from the James Webb Space Telescope (JWST) on the inner two planets verified what I predicted several years ago.<\/p>\n