OUR RESEARCH

AEThER combines astronomy, astrophysics, cosmo- and planetary chemistry, planetary physics and dynamics, experimental and theoretical petrology, and mineral physics to answer fundamental questions about the nature of exoplanetary solar systems and the characteristics that lead rocky planets to have clement surfaces suitable for the development of life. The final product of this project will be a new perspective on what kinds of planets in what stellar environments are most likely to develop habitable surfaces where life can thrive and then be remotely detected.

OUR APPROACH

Principal Investigator

Anat Shahar, Carnegie Institution for science

Proposing Institution

Carnegie Institution for Science, Earth and Planets Laboratory

Participating Institutions

Center for Astrophysics | Harvard & Smithsonian
Howard University
Observatoire de Paris
Pennsylvania State University
University of California Los Angeles
University of Maryland
University of Oxford
University of Rochester
University of Washington

A revolution in astronomy occurred almost 3 decades ago when astronomers discovered the first planet orbiting a Sun-like star outside of our Solar System. Today we know there are thousands of planets orbiting other stars and each of these planetary systems has its own architecture. The next step is to understand the general characteristics of those exoplanets.  The majority of exoplanets have been detected using the transit method where the light from a distant star dims as a planet passes between the star at Earth. This method is most likely to detect exoplanets with orbital periods of days to at most a few years. Longer observing times are needed to detect planets, such as Jupiter with a 12- year orbit, if we are to detect exoplanetary systems more like our own. Carnegie astronomers employ two methods, radial-velocity and astrometry, both of which use ground-based telescopes that provide the opportunity to look for longer period planets.  The detection of planets distant from their star also opens the possibility of direct imaging of the planet with the next generation of telescopes as close-in planets will be difficult to resolve from the blinding light of the host star. A step that is within reach, barely, with the current class of large telescopes is measurement of the composition of exoplanet atmospheres. Detection of water, carbon dioxide, methane, or oxygen in exoplanet atmospheres provides an opportunity to look for the compositional signatures that may be diagnostic of life on the surface of the exoplanet. Detection of time-varying atmospheric compositions, for example in carbon dioxide or sulfur dioxide, may be a signature of a volcanically active planet.Our goal is to explore all these avenues to characterize exoplanets, to find out whether our Solar System is unique, or common, and to focus the search for extraterrestrial life to those exoplanets that are most likely to provide the conditions suitable for the development and sustainment of life.

The presence of a planetary magnetic field is critical for maintaining a habitable environment by magnetically shielding the surface from high-energy charged particles. Its existence hinges on the bulk composition of the mantle and core that controls cooling and solidification rate of the interior. The most basic measurement we need to make of planets is their densities, which we will get from measuring the masses of transiting exoplanets. We also need to measure the compositions of planet-forming material, as a starting point for laboratory measurements and models that translate density into internal structures and dynamics. The bulk composition of a planet depends on the constituents of the star’s protoplanetary disk, i.e., the planetary building blocks, and the mechanisms by which they accumulate to form a planet. Composition will determine material properties associated with heat and mass transport, like melting temperature, thermal and electrical conductivity, viscosity, and the abundance and partitioning of radiogenic isotopes.  Earth is known to have had both an internally generated magnetic field and life over the last 3-4 Gyr, implying that the occurrence of terrestrial magnetic fields and life may be correlated. Determining how the interior differentiates and cools requires experimental studies in mineral physics and geodynamic models.

Volatiles are planetary constituents that evaporate easily but are necessary for habitability, such as water, carbon, and nitrogen. The protoplanetary disks surrounding young stars inherit their elemental composition from the gas that formed their stars, which can vary across the Galaxy. Unless trapped as ices or by reactions within rock, volatiles may evaporate from the disk as the agglomeration of solids small pebbles into comets and asteroids and then into planets proceeds.  Determining volatile inventories available to exoplanets requires integration of astronomical observations of planet-forming disks, measurements of meteorites from our solar system, theoretical simulations of planetary growth, differentiation, and evolution, and complementary experiments necessary to feed into the simulations.

Planetary atmospheres can change over time as volcanic eruptions release gases from the planetary interior and plate tectonics cycles material between the surface and interior. The surface environment is controlled by interactions between the atmosphere, ocean, and crust. Creating and maintaining a surface with liquid water, a temperate climate, and some exposed land requires three components: (1) the right amount of stellar heating, (2) a formation history that allows a primary atmosphere to be outgassed, and (3) geologic sources and sinks that provide long-term volatile cycling. Although stellar heating is controlled by orbital distance, the latter two are controlled by formation, internal dynamics and bulk composition. Determining how the interior affects the surface and atmosphere requires integrating astronomical observations of stars and disks, theoretical simulations of planetary evolution, and experiments to determine what elements go into the different layers of the interior of planets.