Space Studies Board organized a workshop to conduct a systematic cross-disciplinary examination of the state of the field. Its purpose was to assess the current state of the field and identify future studies that might contribute to important research goals in star and planet formation, the frequency of planetary systems, the nature of non-luminous matter on scales up through cosmological, the behavior of matter under extreme conditions, and the evolution of atmospheres of objects ranging in mass from planetary through stellar.

The state of the field as summarized at the workshop by 21 invited experts is vigorous: substellar-mass objects are now being detected or characterized, on a regular basis, by roughly a half dozen different techniques, both ground- and space-based, with additional approaches nearing the maturity necessary to conduct successful searches. Much of the activity is a result of individual or small-team, principal-investigator-based, projects, rather than large-scale “mission-type” programs, although some of the discoveries have been made with instruments (e.g., the Hubble Space Telescope and Keck telescope) that are the result of large-scale public or private programs. Additional to the availability of large or space-based telescopes are the maturation and ready availability of sensitive detector systems. However, a substantial ingredient in the success of the searches is the invention of novel data-processing schemes (in turn enabled by high-speed and high-capacity computers), calibration techniques (such as the iodine cell utilized in the radial-velocity program), and the autocatalytic growth of observing networks linked by electronic mail and able to confirm transient events (e.g., microlensing networks).

Powerful computers also have allowed modeling efforts to move from highly approximate schemes to capabilities more in line with the new data available. In particular, frequency-averaged or “gray” model atmospheres have given way to fully frequency-dependent models, handling tens of millions of spectral lines, essential both for synthesizing spectra to compare with data and for properly characterizing atmospheric energy balance.

The discovery of a cohort of Jupiter-mass planets in close orbits around their parent stars has stimulated more elaborate hydrodynamical models of SMO formation, again enabled by high-speed computers. Because SMO interiors are under high pressure and (except for the most massive or youngest objects) moderately degenerate, the behavior of matter under extreme conditions is a crucial issue in understanding the formation and evolution of these bodies. Theoretical and experimental advances in high-pressure physics have led to improved characterization of the physical properties of SMOs.

FINDINGS

As a result of the presentations and discussions at the workshop and subsequent deliberations, the Steering Group for the Workshop on Substellar-Mass Objects formulated a number of findings about the current state of research related to SMOs. These findings are organized under headings related to the five questions posed in NASA 's request for an examination of pertinent issues (see preface).

Status of Current Research Activities

The study of SMOs is currently in a state of high vigor after several decades of false starts and frustrations. The key to the new successes lies in technological advancements in ground-based telescopes buttressed by results from key spacecraft programs and theoretical studies of growing power and fidelity. The challenge for NASA and other funding agencies is to foster these programs in such a way that they contribute to NASA's ultimate



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