The National Academies Press

Currently Skimming:

Pages 407-433

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 407... ... 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. Read the entire page →
From page 408... ... 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 409... ... The Exoplanet Science Strategy (ESS; NAS 2018) identified two overarching goals: ● Understand the formation and evolution of planetary systems as products of the process of star formation, and characterize and explain the diversity of planetary system architectures, planetary compositions, and planetary environments produced by these processes. Read the entire page →
From page 410... ... Q12.1a How Does a Disk's Bulk Composition Affect the Diversity of Resulting Planetary Materials? Meteoritic studies tell us that the bulk composition of the solar nebula was similar to the composition of the solar photosphere, providing direct evidence that stellar composition can be used to constrain overall circumstellar disk composition (e.g., Johnson et al. Read the entire page →
From page 411... ... Disk observations have begun to probe the earliest stages of planet formation. Estimates of the total mass in sub-cm sized particles in 1 to 3 Myr old disks (Ansdell et al. Read the entire page →
From page 412... ... Saturn. Diverse exoplanet systems display evidence of more complex planetary outcomes. Read the entire page →
From page 413... ... be low. Several lines of exploration within the solar system and of exoplanet systems will help to answer fundamental questions about rocky planet formation. Read the entire page →
From page 414... ... Q12.3c What Processes Produce Compact Exoplanet Systems and How Do They Differ From Conditions in Our Inner Solar System That Yielded No Surviving Planets Interior to Mercury? The existence of compact systems of Earth to sub-Neptune sized planets has been one of the most intriguing discoveries of the Kepler mission. Read the entire page →
From page 415... ... if possible, spin state (e.g., Gratia and Lissauer 2021) Read the entire page →
From page 416... ... FIGURE 15.3. Origin of solid bodies (§12.3) Read the entire page →
From page 417... ... atmospheric properties? Metallic cores are considered the usual location of dynamos, but liquid silicates have sufficient electrical conductivity under high pressure/temperature conditions, suggesting that dynamos could also be generated in magma oceans of, e.g., super-Earths. Read the entire page →
From page 418... ... Q12.6a What Determines the Division Between Gas-Rich and Solid-Body Planets? In the solar system, there is a clear distinction between the four giant planets with puffy hydrogendominated atmospheres and all other solid planetary bodies. Read the entire page →
From page 419... ... Q12.6e What Processes Impact the Evolution of Atmospheric Chemistry, Cloud and Haze Formation in Diverse Planetary Atmospheres? The number of planetary atmospheres in the solar system is limited, but even so great diversity in composition and chemistry is seen. Read the entire page →
From page 420... ... Q12.7 GIANT PLANET STRUCTURE AND EVOLUTION The interior structure of a giant planet is the result of both formation and evolution processes. For many giant exoplanets, both mass and radius have been measured, providing estimates of the density of these planets. Read the entire page →
From page 421... ... Q12.7d What Factors in the Formation and Evolution of Planets Define the Crossover Regime Where a Planet Either Becomes a Super-Earth or a Sub-Neptune? As noted in Q12.2, the most commonly detected exoplanets are super-Earths and sub-Neptunes (see Figure 15.1k and Fulton et al. Read the entire page →
From page 422... ... and/or gravitationally confining ring material. Detection and characterization of exomoons and circumplanetary disks would enhance our understanding of the formation, evolution, and lifetime of circumplanetary systems, as well as the potential for habitable exomoons. Read the entire page →
From page 423... ... biosphere. But Earth would have looked quite different at different times in its history. Read the entire page →
From page 424... ... Q.12.9b What Biosignatures Can Be Sought on Exoplanets Analogous to Earth, Including Past Phases of Earth History? The metabolisms powering life on Earth may produce detectable byproducts, which could be sought as biosignatures in exoplanet atmospheres with future telescopes. Read the entire page →
From page 425... ... Strategic Research for Q12.9 ● Determine the environmental requirements of life on Earth to inform the limits of habitability on exoplanets through field and laboratory investigations, and studies of "extreme" forms of Earthly organisms (e.g., organisms that survive at very low or high temperatures or in high radiation environments) Read the entire page →
From page 426... ... Q12.10b What Constraints Can Be Placed on the Presence of Liquid Water on Exoplanets? The composition of a planet's atmosphere determines surface temperatures via the greenhouse effect, which in turn determines whether surface liquid water can exist. Read the entire page →
From page 427... ... Strategic Research for Q12.10 ● Determine the presence or absence of atmospheres on potentially habitable rocky exoplanets via telescopic observations, including transit spectroscopy, thermal phase curve analyses, and reflected light spectroscopy (NASEM 2021) , and via comparisons to solar system planets. Read the entire page →
From page 428... ... environments so that the plausibility of abiotic explanations can be evaluated, and their environments' habitability assessed. Q12.11b Are Biosignatures Observable on Exoplanets in the Near Future? Read the entire page →
From page 429... ... 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 430... ... Crossfield, I Read the entire page →
From page 431... ... Kaltenegger, L., W.A. Traub, and K.W. Read the entire page →
From page 432... ... Mumma, M.J., G.L. Villanueva, R.E. Read the entire page →
From page 433... ... Shields, A.L., S Ballard and J.A. Read the entire page →

From page 407...

... 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.