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71.
Xu J Ramian GJ Galan JF Savvidis PG Scopatz AM Birge RR Allen SJ Plaxco KW 《Astrobiology》2003,3(3):489-504
We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs. 相似文献
72.
Michael F. A’Hearn Michael J. S. Belton Alan Delamere William H. Blume 《Space Science Reviews》2005,117(1-2):1-21
The Deep Impact mission will provide the first data on the interior of a cometary nucleus and a comparison of those data with
data on the surface. Two spacecraft, an impactor and a flyby spacecraft, will arrive at comet 9P/Tempel 1 on 4 July 2005 to
create and observe the formation and final properties of a large crater that is predicted to be approximately 30-m deep with
the dimensions of a football stadium. The flyby and impactor instruments will yield images and near infrared spectra (1–5
μm) of the surface at unprecedented spatial resolutions both before and after the impact of a 350-kg spacecraft at 10.2 km/s.
These data will provide unique information on the structure of the nucleus near the surface and its chemical composition.
They will also used to interpret the evolutionary effects on remote sensing data and will indicate how those data can be used
to better constrain conditions in the early solar system. 相似文献
73.
Curiosity’s Mars Hand Lens Imager (MAHLI) Investigation 总被引:1,自引:0,他引:1
Kenneth S. Edgett R. Aileen Yingst Michael A. Ravine Michael A. Caplinger Justin N. Maki F. Tony Ghaemi Jacob A. Schaffner James F. Bell III Laurence J. Edwards Kenneth E. Herkenhoff Ezat Heydari Linda C. Kah Mark T. Lemmon Michelle E. Minitti Timothy S. Olson Timothy J. Parker Scott K. Rowland Juergen Schieber Robert J. Sullivan Dawn Y. Sumner Peter C. Thomas Elsa H. Jensen John J. Simmonds Aaron J. Sengstacken Reg G. Willson Walter Goetz 《Space Science Reviews》2012,170(1-4):259-317
The Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) investigation will use a 2-megapixel color camera with a focusable macro lens aboard the rover, Curiosity, to investigate the stratigraphy and grain-scale texture, structure, mineralogy, and morphology of geologic materials in northwestern Gale crater. Of particular interest is the stratigraphic record of a ~5?km thick layered rock sequence exposed on the slopes of Aeolis Mons (also known as Mount Sharp). The instrument consists of three parts, a?camera head mounted on the turret at the end of a robotic arm, an electronics and data storage assembly located inside the rover body, and a calibration target mounted on the robotic arm shoulder azimuth actuator housing. MAHLI can acquire in-focus images at working distances from ~2.1?cm to infinity. At the minimum working distance, image pixel scale is ~14?μm per pixel and very coarse silt grains can be resolved. At the working distance of the Mars Exploration Rover Microscopic Imager cameras aboard Spirit and Opportunity, MAHLI’s resolution is comparable at ~30?μm per pixel. Onboard capabilities include autofocus, auto-exposure, sub-framing, video imaging, Bayer pattern color interpolation, lossy and lossless compression, focus merging of up to 8 focus stack images, white light and longwave ultraviolet (365 nm) illumination of nearby subjects, and 8 gigabytes of non-volatile memory data storage. 相似文献
74.
Hawkins S. Edward Darlington E. Hugo Murchie Scott L. Peacock Keith Harris Terry J. Hersman Christopher B. Elko Michael J. Prendergast Daniel T. Ballard Benjamin W. Gold Robert E. Veverka Joseph Robinson Mark S. 《Space Science Reviews》1997,82(1-2):31-100
A multispectral imager has been developed for a rendezvous mission with the near-Earth asteroid, 433 Eros. The Multi-Spectral Imager (MSI) on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft uses a five-element refractive optical telescope, has a field of view of 2.93 × 2.25°, a focal length of 167.35 mm, and has a spatial resolution of 16.1 × 9.5 m at a range of 100 km. The spectral sensitivity of the instrument spans visible to near infrared wavelengths, and was designed to provide insight into the nature and fundamental properties of asteroids and comets. Seven narrow band spectral filters were chosen to provide multicolor imaging and to make comparative studies with previous observations of S asteroids and measurements of the characteristic absorption in Fe minerals near 1 µm. An eighth filter with a much wider spectral passband will be used for optical navigation and for imaging faint objects, down to visual magnitude of +10.5. The camera has a fixed 1 Hz frame rate and the signal intensities are digitized to 12 bits. The detector, a Thomson-CSF TH7866A Charge-Coupled Device, permits electronic shuttering which effectively varies the dynamic range over an additional three orders of magnitude. Communication with the NEAR spacecraft occurs via a MIL-STD-1553 bus interface, and a high speed serial interface permits rapid transmission of images to the spacecraft solid state recorder. Onboard image processing consists of a multi-tiered data compression scheme. The instrument was extensively tested and calibrated prior to launch; some inflight calibrations have already been completed. This paper presents a detailed overview of the Multi-Spectral Imager and its objectives, design, construction, testing and calibration. 相似文献
75.
76.
Has the current US space policy improved the USA's overall strategic position? Does it affect favorably international partnerships? These questions are examined in terms of security, political economy, and influence. In today's context, where there are more space players, more options, more potential for unintended consequences, and higher stakes, unilateral action is more limited in its effectiveness than in earlier times. Surveying current US space policy, it is not clear that data-driven, analytically based decisions are being made to affect positively national independence, innovation, market creation, and international perceptions of the USA as a trustworthy partner. More promising are the steps taken to bolster a predictable space operational environment and economic competitiveness. Ultimately, in order to achieve American excellence and leadership, a ‘closed loop’ on the policy system is needed, to gauge regularly and systematically whether the US is achieving the desired national outcomes. 相似文献
77.
78.
Michael Potter 《Space Policy》1991,7(2)
The signing of an INF arms control treaty in 1987 and the reduction in East-West tension has resulted in a surplus of missiles. Getting rid of them remains a problem, but two distinct initiatives have been advanced in the USA and the USSR for their conversion into low-cost launchers. The author describes these two initiatives and discusses the political and economic issues they raise before speculating on the likelihood of their achievement. 相似文献
79.
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