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Pages 305-324

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From page 305... ... This is only possible with a large, high-contrast, direct-imaging space telescope. Directly imaging and obtaining spectra of objects 10 billion times fainter than their host stars is a remarkable challenge. Read the entire page →
From page 306... ... 306 PATHWAYS TO DISCOVERY IN ASTRONOMY AND ASTROPHYSICS FOR THE 2020s typically just a few times that of the zodiacal cloud; observations with the Roman CGI may also improve exozodiacal dust constraints. Terrestrial exoplanets now appear to be common enough to detect in substantial numbers with sufficient resources. Read the entire page →
From page 307... ... E-Q3: How do habitable E-Q3a: How are potentially habitable environments formed? environments arise and evolve E-Q3b: What processes influence the habitability of environments? Read the entire page →
From page 308... ... transiting E-Q1e, bright stars and potentially habitable planets objects, exomoons, and planetary ring E-Q2a orbiting KM stars systems PLATO: find planets orbiting bright stars; precisely determine planet and star properties; asteroseismology Read the entire page →
From page 309... ... Radio observations >10 GHz and high resolution Lyman alpha (>~30,000) for photoevaporation and inferring stellar mass loss rates UV observations of E-Q2a, HST limited UV transit capability UV space telescope: R >1,000 spectroscopy; planets and host stars E-Q2c, monitor atmospheric escape; high-contrast E-Q2d, imaging of planets to detect UV absorbers; E-Q3c time-resolved UV stellar flux High-resolution O/IR E-Q2a, R >~1e5 O/IR spectroscopy (8–10 m telescopes) Read the entire page →
From page 310... ... Line, 2018, "Characterizing Earth Analogs in Reflected Light: Atmospheric Retrieval Studies for Future Space Telescopes," Astronomical Journal 155(5) Read the entire page →
From page 311... ... In this complex, turbulent, and dynamic environment, clouds of dense molecular gas are produced that are the sites of star formation. Within these molecular clouds, dense cores form that eventually gravitationally collapse and often fragment further to form stars with a wide range of masses. Read the entire page →
From page 312... ... Shifting to local studies of Milky Way molecular clouds, there have been substantial developments in our understanding of the many relevant physical scales and processes associated with star formation. Surveys of local star-forming regions with Spitzer provided the first complete censuses of their low-mass protostars and analyzed their spatial distributions relative to the cloud structures. Read the entire page →
From page 313... ... have substantially improved estimates of young star luminosities and thereby ages, an essential aspect of characterizing the star formation histories of molecular clouds as well as for establishing protoplanetary disk lifetimes. Additional measurements of precise kinematics of young stellar populations from Gaia have increased the number of known nearby clusters and moving groups, facilitating more robust investigations of their initial mass functions, chemical homogeneity, and multiplicity statistics as a function of age. Read the entire page →
From page 314... ... Laboratory experiments, including microgravity studies of dust particle collisions, chemical measurements of ice mantle formation and sublimation, and analyses of meteorites, provide critical inputs for both theoretical models and the interpretation of astronomical data. Building on these many achievements over the past decade, this appendix discusses the opportunities for making further progress in characterizing and understanding the state of the ISM in the Milky Way and nearby galaxies, star formation, and planet formation, greatly assisted and informed by the contributions of more than 150 science white papers from the broader community. Read the entire page →
From page 315... ... Studying the formation of molecular clouds requires observations of regions where dramatic changes in temperature, density, and chemistry are occurring. In particular, it is critical to track the "CO-dark" gas, where CO is underabundant. Read the entire page →
From page 316... ... (Right) Three-phase Interstellar Medium in Galaxies Resolving Evolution with Star Formation and Supernova Feedback (TIGRESS) Read the entire page →
From page 317... ... F-Q2b. What Is the Origin and Prevalence of High-Density Structures in Molecular Clouds and What Role Do They Play in Star Formation? Read the entire page →
From page 318... ... While filaments likely dominate the mass budget of the dense molecular gas where stars form, the understanding of their formation, fragmentation, as well as the degree to which they contain sub-structure remain controversial. Furthermore, it is not clear whether filaments are a widespread and critical step in star formation across galaxies of different properties. Read the entire page →
From page 319... ... , is needed to distinguish heating by turbulent dissipation, stellar radiation, and/or cosmic rays. To address the role of magnetic fields in cloud structure and dynamics, high-resolution (<0.1 pc, ~10" [arcsec] Read the entire page →
From page 320... ... Insights on how magnetic fields mediate the collapse process can also be obtained from measurements of field morphologies -- for example, from polarized submillimeter to centimeter dust emission and Zeeman splitting from key molecular line tracers. With such refined observational constraints, we can assess core lifetimes, their susceptibility to fragmentation and binary star formation, and ultimately the link between core masses and the stellar IMF. Read the entire page →
From page 321... ... are especially important for probing high-mass star formation in environments with very high dust extinction, as well as better penetration of high optical depths in the densest parts (generally smallestscales) of infalling low-mass cores. Read the entire page →
From page 322... ... IS PLANET FORMATION FAST OR SLOW? A robust determination of the epoch of planet formation is a challenge for the coming decade. Read the entire page →
From page 323... ... , and magnetic fields. Read the entire page →
From page 324... ... in disks. Aside from better characterizing the different potential transport process, continued efforts to measure turbulence are highly desirable because of the diverse roles it plays in planet formation -- from limiting the collisional growth of solids, to affecting the formation of planetesimals, and beyond to regulating the structures of gaps and the migration of protoplanets in gas disks. Read the entire page →

From page 305...

... This is only possible with a large, high-contrast, direct-imaging space telescope. Directly imaging and obtaining spectra of objects 10 billion times fainter than their host stars is a remarkable challenge.