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From page 391... ... 15 Question 12: Exoplanets What does our planetary system and its circumplanetary systems of satellites and rings reveal about other planetary systems, and what can disks and exoplanets orbiting other stars teach us about the solar system? The past decade has seen extraordinary growth in our knowledge of planetary systems around other stars, as well as in the conditions of planet formation and the remarkable diversity and abundance of exoplanets.1 These advances have been supported by continuing exoplanet discoveries, ground-breaking observations afforded in part by new facilities, and a progression from planet detection to detailed study and characterization of individual planets. Read the entire page →
From page 393... ... QUESTION 12: EXOPLANETS 393 FIGURE 15-1 A selection of discoveries in exoplanet research in the past decade, with a layout intended to capture the explosive recent expansion of scientific understanding. Read the entire page →
From page 394... ... 394 ORIGINS, WORLDS, AND LIFE FIGURE 15-2 Exoplanets currently detected by Kepler (red) and other means (black) Read the entire page →
From page 395... ... QUESTION 12: EXOPLANETS 395 protoplanetary nebula. Coordinating research between studies of these disks and models of solar system formation can greatly advance our understanding of planetary system formation. Read the entire page →
From page 396... ... 396 ORIGINS, WORLDS, AND LIFE exoplanet system masses, suggesting that solids may have already accreted into larger (≥ cm) sizes by this time (Manara et al. Read the entire page →
From page 397... ... QUESTION 12: EXOPLANETS 397 Q12.2b Is the Solar System Architecture, with Multiple Outer Giant Planets That Formed Beyond the Water Ice Line, a Common or Uncommon Outcome of Planet Formation in the Galaxy? How Common Was Giant Planet Migration? Read the entire page →
From page 398... ... 398 ORIGINS, WORLDS, AND LIFE matches the overall composition of elements heavier than helium in primitive meteorites. Whether stellar composition in general is a proxy for planet composition can be begun to be assessed by measuring volatile-poor and volatile-rich exoplanet bulk densities. Read the entire page →
From page 399... ... QUESTION 12: EXOPLANETS 399 Strategic Research for Q12.3 • Determine noble gas abundances and isotope ratios, and the stable isotope ratios in the atmospheres of Venus and Mars with spacecraft observations and in situ probes. • Characterize exoplanets smaller than sub-Neptunes, including their mass–radius relations, surface or atmospheric emission, and orbital period ratios with telescopic observations and modeling studies. Read the entire page →
From page 400... ... 400 ORIGINS, WORLDS, AND LIFE Strategic Research for Q12.4 • Determine the physical and orbital properties of exoplanets in multi-planet systems to understand their dynamical histories with telescopic observations. • Characterize impact conditions that would produce detectable dust signatures in exoplanetary systems with numerical simulations and models. Read the entire page →
From page 401... ... QUESTION 12: EXOPLANETS 401 FIGURE 15-3 Origin of solid bodies (Q12.3) and their evolution (Q12.5) Read the entire page →
From page 402... ... 402 ORIGINS, WORLDS, AND LIFE • Determine how solid bodies over a broad range of conditions relevant to exoplanets evolve through geologic time with modeling and theoretical research on processes including, for example, solidification of magma oceans; solid-state mantle convection; thermally and chemically driven dynamics in metallic cores; and dynamos generated in liquid metals and silicates. • Determine thermophysical properties of ices, silicates, and metal alloys under the ranges of pressure and temperature conditions and compositions relevant to exoplanets with first-principles simulations and laboratory experiments. Read the entire page →
From page 403... ... QUESTION 12: EXOPLANETS 403 Q12.6d How Does the Evolution of the Host Star Affect Planetary Atmospheres, Including Photochemistry and Escape Processes? The Sun's changing output has had a dramatic impact on atmospheric evolution in the solar system, and the effect of host stars on exoplanets is likely to be similarly important. Read the entire page →
From page 404... ... 404 ORIGINS, WORLDS, AND LIFE • Determine the connection between exoplanet observables and atmospheric properties and dynamics by conducting theoretical and modeling studies to include the following: simulations (1D and 3D) with hazes and clouds; radiative-microphysical feedbacks; volatile transfer between atmospheres and surfaces; and interactions with the solar wind including the influence of magnetic fields on atmospheric escape processes. Read the entire page →
From page 405... ... QUESTION 12: EXOPLANETS 405 Uranus and Neptune and what this can tell us about sub-Neptune magnetic field generation remains uncertain, owing to very incomplete knowledge of the Uranus and Neptune field configurations and properties. Q12.7d What Factors in the Formation and Evolution of Planets Define the Crossover Regime Where a Planet Becomes Either a Super-Earth or a Sub-Neptune? Read the entire page →
From page 406... ... 406 ORIGINS, WORLDS, AND LIFE Q12.8a What Can Observations of Circumplanetary Material Reveal About the Formation and Evolution of Circumplanetary Systems? The composition of rings and moons hinges on conditions in their precursor circumplanetary disks, as well as their subsequent evolution. Read the entire page →
From page 407... ... QUESTION 12: EXOPLANETS 407 Q12.9a Which Among the Necessary Ingredients and Conditions Required by Life on Earth Can Be Inferred or Detected on Exoplanets? All known life requires the presence of liquid water as a solvent in which oxidation and reduction reactions can occur. Read the entire page →
From page 408... ... 408 ORIGINS, WORLDS, AND LIFE Q12.9c What Can We Learn About False Positive and False Negative Detection of Life on Exoplanets from Earth History? Environmental contextual information will be critical to distinguish true biosignatures from abiotic "false positive" mimics. Read the entire page →
From page 409... ... QUESTION 12: EXOPLANETS 409 Q12.10 DYNAMIC HABITABILITY The geologic records of Earth, Mars, and Venus show us that planetary habitability is highly variable in space and time. Exoplanet observations soon will offer us the opportunity to address fundamental questions about how a planet's habitability depends on orbital distance, mass, stellar type and other factors. Read the entire page →
From page 410... ... 410 ORIGINS, WORLDS, AND LIFE Q12.10d How Does Atmospheric Chemical Evolution Affect Habitability? Atmospheric chemistry is critical to habitability and the emergence of life. Read the entire page →
From page 411... ... QUESTION 12: EXOPLANETS 411 have generated considerable discussion in the literature in recent decades (e.g., McKay et al. Read the entire page →
From page 412... ... 412 ORIGINS, WORLDS, AND LIFE SUPPORTIVE ACTIVITIES FOR QUESTION 12 • Observations of solar system planets and moons through transit spectroscopy and direct-imaging as analogs to exoplanet observations, including hemispherically averaged fluxes as a function of orbital phase and time; observations of particle and gas opacity in the giant planets and Venus as a function of phase angle to help determine the dependence of reflectivity and scattering on particles and clouds in exoplanet atmospheres; and ultraviolet-/near-infrared-scattered light observations from the poles of the giant planets for comparison with future direct imaging of giant exoplanets. • A census of protoplanetary disks, young planets, and mature planetary systems across a wide range of planet–star separations to determine how the initial composition and conditions in a protoplanetary disk influence the diversity of resulting planets. Read the entire page →
From page 413... ... QUESTION 12: EXOPLANETS 413 DeMeo, F., and B Carry. Read the entire page →
From page 414... ... 414 ORIGINS, WORLDS, AND LIFE Laneuville, M., C Read the entire page →
From page 415... ... QUESTION 12: EXOPLANETS 415 Reinhard, C.T., S.L. Olson, E.W. Read the entire page →

From page 391...

... 15 Question 12: Exoplanets What does our planetary system and its circumplanetary systems of satellites and rings reveal about other planetary systems, and what can disks and exoplanets orbiting other stars teach us about the solar system? The past decade has seen extraordinary growth in our knowledge of planetary systems around other stars, as well as in the conditions of planet formation and the remarkable diversity and abundance of exoplanets.1 These advances have been supported by continuing exoplanet discoveries, ground-breaking observations afforded in part by new facilities, and a progression from planet detection to detailed study and characterization of individual planets.