ISSN:0094-243X    

DOI:10.1063/1.39307

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new scientific discipline has emerged in recent years, stimulated partly by advances in instrumental capability and partly by scientific discoveries. It is the study of systems of planets—their origins, existence, and properties—and of the interactive processes which link the planets with their central star. Two broad foci exist in this field—the first is the study of ‘‘other planetary systems.’’ For evolved systems, this means the detection and characterization of planets around the nearby stars, while for systems still in their natal phase it means the investigation of processes in regions where stars and planets may be forming. The second focus is the study of ‘‘our planetary system’’—the paradigm whose origin and evolution (both past and future) we wish to understand, and which affects us most directly. It is the thesis of this paper that the study of planetary systems will be a key discipline of the 21st century, and that it requires several observatories on the moon for its ultimate development.

ISSN:0094-243X    

DOI:10.1063/1.39347

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39300

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39302

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We consider uses of observatories on the Moon for addressing problems in composition and structure of planetary atmospheres. The focus is on the science which can be uniquely done from the Moon or, at least, best done from the Moon. These fall into three categories, phenomena close to the solar direction, phenomena requiring removal from the near‐Earth environment for observation (e.g., phenomena requiring continuous time coverage over time scales of hours, observations required outside the magnetosphere, and observations required away from the geocorona), and phenomena not observable from the Earth’s surface which require very large telescopes or interferometric arrays.

ISSN:0094-243X    

DOI:10.1063/1.39309

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Observations of the long‐term variations in the motions and morphology of the cloud systems in the atmospheres of Jupiter, Saturn, Uranus and Neptune have been hampered by terrestrial atmospheric effects, a limited range of accessible band passes, the necessity to sacrifice spectral resolution to achieve reasonable spatial resolution, and the inability to observe the planets when they are near the sun. A lunar‐based observatory would allow an intensive, coordinated observing program which could optimize both spatial and spectral resolution of the dynamic structures in the Jovian (Jupiter and Saturn) and Neptunian (Uranus and Neptune) atmospheres. The lunar site would eliminate many of the observing obstacles. During the early phases of lunar development, an optical telescope of the 1–2.5 meter class, equipped with an adequate sunshade, will make an effective long‐term contribution to our understanding of cloud variability in the Jovian and Neptunian atmospheres. Although a larger IR‐optimized facility would provide finer spatial resolution of the data in the 7‐micron region and yield a sensitive probe for temperature variations above the clouds, a 1–2.5 meter class telescope in the airless environment of the moon will provide adequate belt‐zone discrimination on Jupiper at these wavelengths. Tunable filters, allowing a judicious selection of frequency intervals within the methane absorption bands, will allow specific tailoring of the observing sequences to optimize the altitude discrimination, while minimizing data rates.

ISSN:0094-243X    

DOI:10.1063/1.39363

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39351

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39358

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Excess infrared radiation above photospheric levels provides the basis for diagnosing the presence of circumstellar disks surrounding solar‐type pre‐main sequence (PMS) stars, and for determining the evolutionary timescales for these disks. Analysis of a large and representative sample ofcurrently knownsolar‐type PMS stars in Taurus‐Auriga shows that for those stars with agest<3 Myr, ∼1/2 exhibit excess 2.2 &mgr;m and 10 &mgr;m emission consistent with that expected from optically thick disks extending inward to the stellar surface. By an aget∼10 Myr, fewer than 10% of our sample show evidence of dust emission from optically thick disks, and hence must have accreted or destroyed their disks, or may have begun to assemble distributed gas and dust into larger bodies. Hence, the timescale over which diskssurviveas infrared‐luminous, optically thick structures ist≤10 Myr. Out of a sample which contains 33 solar‐type PMS stars surrounded by optically thick disks (typical age,t∼3 Myr), 3 show evidence of inner holes. These holes are signified by small near‐infrared (&lgr;≤25 &mgr;m) excesses arising in optically thin regions located atr<1 AU, and large far‐infrared excesses produced in regionsr≳1 AU. Disks with inner holes may be ‘‘transition structures’’ which have begun to assemble material into larger bodies in the terrestrial planet region. The frequency of occurrence of transition structures in our sample suggests that agivendisk evolves from an optically thick disk to an optically thin structure on a timescale,t∼0.3 Myr. Those stars whose disks have become optically thin in their inner regions show no evidence of either 1) excess optical and ultraviolet radiation believed to be produced in a boundary layer, or 2) strong H&agr; and broad forbidden line emission thought to arise in energetic winds.

ISSN:0094-243X    

DOI:10.1063/1.39359

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper studies the problem of using a telescope like the Hubble Space Telescope (HST), only larger and sensitive to a wider range of wavelengths, to image systems of planets like the solar system around other stars. We treat both reflected starlight and thermal radiation from the planets. We include the instrumental effects of aperture diffraction, scattering due to the Power Spectral Density (PSD) of telescope mirror surface errors, and telescope thermal emission. We compute the integration time required to achieve a signal‐to‐noise ratio (S/N)=5 for photon‐statistical random errors only, which is a necessary but not sufficient criterion for detection at a confidence level of 5 standard deviations. A cold telescope on the Moon with 16 m aperture and the optical quality of HST could detect and characterize planets around nearby stars. Its scientific capabilities would be particularly powerful in the infrared. Because the planet signals are generally weaker than the background, sources of systematic error require careful scrutiny.

ISSN:0094-243X    

DOI:10.1063/1.39365

出版商:AIP    

年代:1990

数据来源: AIP