Key Questions Guiding SEEC Research
Are We Alone in the Universe?
Does life exist on other planets, and if so, how do we know what to look for? Identifying and understanding the necessary ingredients for a planet to support life is one of NASA’s greatest science goals. By studying ways that a planet responds to its surrounding environment, SEEC researchers are pioneering methods to detect life on other worlds. For example, life on Earth has evolved with the planet’s environment, producing changes in the atmosphere called "biosignatures," telltale signs that the planet supports life. Oxygen produced through photosynthesis is considered modern Earth’s primary biosignature. Different planets may have different types of dominant biosignatures, such as biogenic methane and organic haze. In tandem with considerations of possible biosignatures, it is also critical to consider biosignature “false positive” biosignatures generated by abiotic processes to determine how to distinguish them from true signs of life.
Studies of biosignatures must consider how life both acts on and is impacted by its environment. Thanks to a diverse set of scientific expertise and cutting-edge modeling tools, SEEC research can tackle these problems from an interdisciplinary perspective, examining how possible biosignatures can be affected by a planet’s atmospheric, oceanic, climatic, stellar, geological, and biological systems. For example, biosignatures can be impacted by the star a planet orbits. Stars with different ultraviolet radiation levels will cause different chemical makeups of planets’ atmospheres, and different colors of stars could drive the evolution of different vegetation pigments on a planet’s surface.
Related Researchers
Vladimir Airapetian, Giada Arney, Shawn Domagal-Goldman, Nancy Kiang, Ravi Kopparapu, Avi Mandell, Elisa Quintana, Tom Barclay, Melissa Trainer, Geronimo Villanueva
Related SEEC Projects
- Arney et al. - "Atmos: Studies of Exoplanet Atmospheres Enabled by a Versatile 1-D Photochemical-Climate Model"
- Kiang et al. - "Land Planets: Foundations for Understanding the Distribution of Surface Habitability and Life Inside the Habitable Zone"
- Kopparapu et al. - "Determining the Atmospheric Composition and Rotation Rates of Habitable Zone M-dwarfs Planets with Thermal Phase Curves and Transit Spectra"
- Quintana et al. - "Where to Search for Habitable Worlds"
How Do Planets Work?
What factors influence the composition of a planet’s interior, surface, and atmosphere, and what can we detect about these processes across interstellar distances? Many different physical, chemical, and geological processes combine to produce the observable characteristics of a planet’s environment. In the future, some of these characteristics will be visible through powerful NASA telescopes. In order to detect a planet’s distinct traits, however, researchers must better understand how these processes affect each other and change over time.
There are so many important components that make a planet unique, including global circulation dynamics, photochemistry, top-of-atmosphere escape processes, hydrological cycles, volcanism, outgassing, and climate. In order to define a planet’s environment and assess whether it could support life, researchers must develop a complete picture of how these processes interact and evolve over time. To better understand these processes and their observable consequences, SEEC researchers are using a variety of models, including global climate models, photochemical models, and atmospheric escape models.
Related Researchers
Vladimir Airapetian, Giada Arney, Tony Del Genio, Shawn Domagal-Goldman, Thomas Fauchez, Alex Glocer, Scott Guzewich, Wade Henning, Nancy Kiang, Ravi Kopparapu, Weijia Kuang, Avi Mandell, Luke Oman, Alex Pavlov, Jeremy Schnittman, Linda Sohl, Kostas Tsigaridis, Michael Way
Related SEEC Projects
- Airapetian et al. - "Measuring Magnetic Field Effects in Hot Gas Giants: Implications for Atmospheric Loss"
- Arney et al. - "Atmos: Studies of Exoplanet Atmospheres Enabled by a Versatile 1-D Photochemical-Climate Model"
- Fauchez et al. - "Clouds and Hazes: Critical parameters to assess rocky exoplanet habitability with JWST?"
- Glocer et al. - "Dynamics of Upper Atmospheres of Terrestrial Exoplanets Around Active K to M dwarfs as a Factor of Habitability"
- Guzewich et al. - "Simulating Factors Influencing Habitable Exoplanets with ROCKE3D"
- Kiang et al. - "Land Planets: Foundations for Understanding the Distribution of Surface Habitability and Life Inside the Habitable Zone"
- Kopparapu et al. - "Determining the Atmospheric Composition and Rotation Rates of Habitable Zone M-dwarfs Planets with Thermal Phase Curves and Transit Spectra"
- Kuang et al. – "Habitability of Magnetic Exo Terrestrial Planets"
- Lopez et al. - "Steam Worlds not Water Worlds: Assessing The Maximum Size of Habitable Planets"
- Lopez et al. - "Photo-evaporative Atmospheric Escape Across Parameter Space"
- Pavlov et al. - "Ion molecular reactions in the planetary atmospheres. Applications to current Mars, early Mars, early Earth and exoplanets
- Quintana et al. - "Where to Search for Habitable Worlds"
- Schnittman et al. - "Modeling eccentricity effects with chemistry-coupled GCM simulations"
What makes a planet habitable?
A planet’s habitability, or ability to harbor life, results from a complex network of interactions between the planet itself, the system it’s a part of, and the star it orbits. The standard definition for a habitable planet is one that can sustain life for a significant period of time. As far as researchers know, this requires a planet to have liquid water. To detect this water from space, it must be on the planet’s surface. The region around a star where liquid surface water can exist on a planet’s surface is called the “habitable zone.” However, this definition is confined to our understanding of current and past life on Earth and the environments present on other planets. As researchers learn more and discover new environments in which life can sustain itself, the requirements for life on other planets may be redefined.
Different types of planets may drive processes that help or hinder habitability in different ways. For example, planets orbiting low-mass stars in the habitable zone may be tidally locked, with only one hemisphere facing the star at all times. Some planets may be limited to only periodic or local habitable regions on the surface if, e.g., they experience periodic global glaciations or are mostly desiccated. In order to understand the full range of planetary environments that could support life and generate detectable biosignatures, we require more detailed and complete models of diverse planetary conditions. In particular, understanding the processes that can maintain or lead to the loss of habitability on a planet requires the use of multiple coupled models that can examine these processes in detail, especially at the boundaries where these processes intersect each other.
Related Researchers
Vladimir Airapetian, Giada Arney, Tony Del Genio, Shawn Domagal-Goldman, Thomas Fauchez, Alex Glocer, Scott Guzewich, Nancy Kiang, Ravi Kopparapu, Weijia Kuang, Avi Mandell, Luke Oman, Jeremy Schnittman, Linda Sohl, Kostas Tsigaridis, Michael Way
Related SEEC Projects
- Arney et al. - "Atmos: Studies of Exoplanet Atmospheres Enabled by a Versatile 1-D Photochemical-Climate Model"
- Glocer et al. - "Dynamics of Upper Atmospheres of Terrestrial Exoplanets Around Active K to M dwarfs as a Factor of Habitability"
- Guzewich et al. - "Simulating Factors Influencing Habitable Exoplanets with ROCKE3D"
- Kiang et al. - "Land Planets: Foundations for Understanding the Distribution of Surface Habitability and Life Inside the Habitable Zone"
- Kuang et al. – "Habitability of Magnetic Exo Terrestrial Planets"
- Schnittman et al. - "Modeling eccentricity effects with chemistry-coupled GCM simulations"
- Way et al. - "Impact of Extreme Space Weather on Climates of Terrestrial-Type Exoplanets"
Finding Habitable Planets
How do we find life outside our solar system? We start by looking for planets that resemble Earth, the only planet we know of that is habitable. This means we look for planets that are roughly the same size as Earth and orbit the right distance from their star to support liquid water at the surface, known as the habitable zone. Early planet hunters, like NASA’s Kepler/K2 mission, have discovered thousands of planets orbiting distant stars, including several that are small, like Earth, and reside in their star’s habitable zone. NASA’s Transiting Exoplanet Survey Satellite (TESS), will search for small planets that orbit stars in our solar neighborhood. Because these planets are much closer to us than the planets discovered by Kepler/K2, astronomers will be better able to characterize them and potentially find some with solid surfaces and detectable atmospheres.
The planets TESS discovers will be the touchstone planets for many years to come, allowing more powerful telescopes like the upcoming James Webb Space Telescope to look at them in greater detail. The Webb telescope will be able to probe planet atmospheres and look for biosignatures that could only be attributed to life on that planet. Future missions may one day directly image other planets, allowing researchers to complete a census of our galaxy and better understand not only if other habitable planets exist, but how common they are.
Related Researchers
Vladimir Airapetian, Giada Arney, Shawn Domagal-Goldman, Thomas Fauchez, Ravi Kopparapu, Avi Mandell, Tyler Groff, Eric Lopez, Michael McElwain, Aki Roberge, Neil Zimmerman, Maxime Rizzo, Bill Danchi
Related SEEC Projects
- Fauchez et al. - "Clouds and Hazes: Critical parameters to assess rocky exoplanet habitability with JWST?"
- Kopparapu et al. - "Determining the Atmospheric Composition and Rotation Rates of Habitable Zone M-dwarfs Planets with Thermal Phase Curves and Transit Spectra"
- Lopez et al. - "Steam Worlds not Water Worlds: Assessing The Maximum Size of Habitable Planets"
- McElwain et al. - "Exoplanet Spectroscopy Technologies"
What Can Earth Tell Us About Exoplanets?
Earth is our only example of a planet that is habitable and inhabited. For this reason, it is the prime example researchers look to when understanding habitability and life that may exist elsewhere. Using Earth as a model, researchers can use information about its environment to better understand the habitability of other planets in our solar system and beyond. Scientists can also apply what is known about Earth to study the histories of other planets and whether they may have once been able to support life. These analyses may consider factors such as the chemical evolution of Earth’s atmosphere through time, its atmospheric dynamics and loss, and the impact of surface and biological processes on the environment. The rich data available on Earth can also be used to validate exoplanet models, making these tools more applicable to a diverse array of worlds. Extending these validated models to other planetary systems, such as by varying the orbit and type of host star, will allow researchers to consider what impacts these processes have on a planet’s ability to support life.
Just as Earth can guide our understanding of other habitable worlds, exoplanets can help us place Earth and our solar system into a broader context, informing us of how common habitable conditions are. Exoplanets at earlier stages of evolution could also shed light on processes that operated on Earth or other planets in the solar system in the past. Discovering and exploring other habitable worlds will help us understand whether Earth and other planets in our solar system are rare or simply a standard outcome of planetary formation.
Related Researchers
Vladimir Airapetian, Giada Arney, Tony Del Genio, Shawn Domagal-Goldman, Thomas Fauchez, Alex Glocer, Scott Guzewich, Nancy Kiang, Ravi Kopparapu, Weijia Kuang, Avi Mandell, Luke Oman, Jeremy Schnittman, Linda Sohl, Kostas Tsigaridis, Michael Way
Related SEEC Projects
"Atmos: Studies of Exoplanet Atmospheres Enabled by a Versatile 1-D Photochemical-Climate Model" "Dynamics of Upper Atmospheres of Terrestrial Exoplanets Around Active K to M dwarfs as a Factor of Habitability" - Guzewich et al. - "Simulating Factors Influencing Habitable Exoplanets with ROCKE3D"
- Kiang et al. - "Land Planets: Foundations for Understanding the Distribution of Surface Habitability and Life Inside the Habitable Zone"
- Kuang et al. – "Habitability of Magnetic Exo Terrestrial Planets"
- Schnittman et al. - "Modeling eccentricity effects with chemistry-coupled GCM simulations"
- Way et al. - "Impact of Extreme Space Weather on Climates of Terrestrial-Type Exoplanets"
