Smithsonian at the Poles: Contributions to International Polar

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Cosmology from Antarctica Robert W. Wilson and Antony A. Stark Robert W. Wilson and Antony A. Stark, Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA. Corresponding author: R. W. Wilson (rwilson@cfa.harvard.edu). Accepted 25 June 2008. ABSTRACT. Four hundred thousand years after the Big Bang, electrons and nuclei combined to form atoms for the fi rst time, allowing a sea of photons to stream freely through a newly transparent universe. After billions of years, those photons, highly redshifted by the universal cosmic expansion, have become the cosmic microwave background (CMB) radiation we see coming from all directions today. Observation of the CMB is central to observational cosmology, and the Antarctic plateau is an exceptionally good site for this work. The fi rst attempt at CMB observations from the plateau was an expedition to the South Pole in December 1986 by the Radio Physics Research group at Bell Laboratories. No CMB anisotropies were observed, but sky noise and opacity were measured. The results were suffi ciently encouraging that in the austral summer of 1988– 1989, three CMB groups participated in the “Cucumber” campaign, where a temporary site dedicated to CMB anisotropy measurements was set up 2 km from South Pole Station. These were summer-only campaigns. Wintertime observations became possible in 1990 with the establishment of the Center for Astrophysical Research in Antarctica (CARA), a National Science Foundation Science and Technology Center. The CARA developed year-round observing facilities in the “Dark Sector,” a section of Amundsen– Scott South Pole Station dedicated to astronomical observations. The CARA scientists fi elded several astronomical instruments: Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), South Pole Infrared Explorer (SPIREX), White Dish, Python, Viper, Arcminute Cosmology Bolometer Array Receiver (ACBAR), and Degree-Angular Scale Interferometer (DASI). By 2001, data from CARA, together with that from Balloon Observations of Millimetric Extragalactic Radiation and Geophysics (BOOMERANG— a CMB experiment on a long-duration balloon launched from McMurdo Station on the coast of Antarctica) showed clear evidence that the overall geometry of the universe is fl at, as opposed to being positively or negatively curved. In 2002, the DASI group reported the detection of polarization in the CMB. These observations strongly support a “concordance model” of cosmology, where the dynamics of a fl at universe are dominated by forces exerted by the mysterious dark energy and dark matter. The CMB observations continue on the Antarctic plateau. The South Pole Telescope (SPT) is a newly operational 10-m-diameter offset telescope designed to rapidly measure anisotropies on scales much smaller than 1°. INTRODUCTION Cosmology has made tremendous strides in the past decade; this is generally understood within the scientifi c community, but it is not generally appreciated that some of the most important results have come from Antarctica. Observational
360 SMITHSONIAN AT THE POLES / WILSON AND STARK cosmology has become a quantitative science. Cosmologists describe the universe by a model with roughly a dozen parameters, for example, the Hubble constant, H0, and the density parameter, �. A decade ago, typical errors on these parameters were 30% or greater; now, most are known within 10%. We can honestly discriminate for and against cosmological hypotheses on the basis of quantitative data. The current concordance model, Lambda– Cold Dark Matter (Ostriker and Steinhardt, 1995), is both highly detailed and consistent with observations. This paper will review the contribution of Antarctic observations to this great work. From the fi rst detection of the cosmic microwave background (CMB) radiation (Penzias and Wilson, 1965), it was understood that deviations from perfect anisotropy would advance our understanding of cosmology (Peebles and Yu, 1970; Harrison, 1970): the small deviations from smoothness in the early universe are the seeds from which subsequent structure grows, and these small irregularities appear as differences in the brightness of the CMB in various directions on the sky. When the universe was only 350,000 years old, the CMB radiation was released by electrons as they combined with nuclei into atoms for the fi rst time. Anisotropies in the CMB radiation indicate slight differences in density and temperature that eventually evolve into stars, galaxies, and clusters of galaxies. Observations at progressively higher sensitivity by many groups of scientists from the 1970s through the 1990s failed to detect the anisotropy (cf. the review by Lasenby et al., 1998). In the course of these experiments, observing techniques were developed, detector sensitivities were improved by orders of magnitude, and the effects of atmospheric noise became better understood. The techniques and detectors were so improved that the sensitivity of experiments came to be dominated by atmospheric noise at most observatory sites. Researchers moved their instruments to orbit, to balloons, and to high, dry observatory sites in the Andes and in Antarctica. Eventually, CMB anisotropies were detected by the Cosmic Background Explorer satellite (COBE; Fixsen et al., 1996). The ground-based experiments at remote sites also met with success. The spectrum of brightness in CMB variations as a function of spatial frequency was measured by a series of ground-based and balloon-borne experiments, many of them located in the Antarctic. The data were then vastly improved upon by the Wilkinson Microwave Anisotropy Probe (WMAP; Spergel et al., 2003). The future Planck satellite mission (Tauber, 2005), expected to launch in 2008, will provide high signal-to-noise data on CMB anisotropy and polarization that will reduce the error on some cosmological parameters to the level of 1%. Even in the era of CMB satellites, ground-based CMB observations are still essential for reasons of fundamental physics. Cosmic microwave background radiation occurs only at wavelengths longer than 1 mm. The resolution of a telescope (in radians) is equal to the observed wavelength divided by the telescope diameter. To work properly, the overall accuracy of the telescope optics must be a small fraction of a wavelength. Observing the CMB at resolutions of a minute of arc or smaller therefore requires a telescope that is 10 m in diameter or larger, with an overall accuracy of 0.1 mm or better. There are no prospects for an orbital or airborne telescope of this size and accuracy in the foreseeable future. There is, however, important science to be done at high resolution, work that can only be done with a large ground-based telescope at the best possible ground-based site— the Antarctic plateau. DEVELOPMENT OF ASTRONOMY IN THE ANTARCTIC Water vapor is the principal source of atmospheric noise in radio observations. Because it is exceptionally cold, the climate at the South Pole implies exceptionally dry observing conditions. As air becomes colder, the amount of water vapor it can hold is dramatically reduced. At 0°C, the freezing point of water, air can hold 83 times more water vapor than saturated air at the South Pole’s average annual temperature of �49°C (Goff and Gratch, 1946). Together with the relatively high altitude of the South Pole (2850 m), this means the water vapor content of the atmosphere above the South Pole is two or three orders of magnitude smaller than it is at most places on the Earth’s surface. This has long been known (Smythe and Jackson, 1977), but many years of hard work were needed to realize the potential in the form of new astronomical knowledge (cf. the recent review by Indermuehle et al., 2006). A French experiment, Emission Millimetrique (EMI- LIE) (Pajot et al., 1989), made the fi rst astronomical observations of submillimeter waves from the South Pole during the austral summer of 1984– 1985. Emission Millimetrique was a ground-based, single-pixel bolometer dewar operating at λ900�m and fed by a 45-cm off-axis mirror. It had successfully measured the diffuse galactic emission while operating on Mauna Kea in Hawaii in 1982, but the accuracy of the result had been limited by sky noise (Pajot et al., 1986). Martin A. Pomerantz, a cosmic ray researcher at Bartol Research Institute, encouraged the EMILIE group to relocate their experiment to the South Pole (Lynch, 1998).
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Smithsonian at the Poles Contributi
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Contents FOREWORD by Ira Rubinoff i
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Elaina Jorgensen, Alaska Fisheries
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CONTENTS vii Watching Star Birth fr
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x SMITHSONIAN AT THE POLES blooms i
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xii SMITHSONIAN AT THE POLES Change
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xiv SMITHSONIAN AT THE POLES Museum
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Advancing Polar Research and Commun
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James P. Espy (1785- 1860), the fi
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ology fueled hopes that the scienti
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Meteorologists also provided critic
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visualize weather patterns remotely
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in ice sheets. The latest collapse
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Cooperation at the Poles? Placing t
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British Association for the Advance
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cations, in which the Smithsonian s
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ence” (Robinson, 2006: 76), he ha
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Taylor, C. J. 1981. First Internati
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24 SMITHSONIAN AT THE POLES / KORSM
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36 SMITHSONIAN AT THE POLES / De VO
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From Ballooning in the Arctic to 10
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ern Svalbard in 1896 (Capelotti, 19
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FIGURE 2. The Andrée campsite in 1
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National Zoo in Washington, D.C.—
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FROM BALLOONING TO 10,000-FOOT RUNW
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e rapidly deployed to South America
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“Of No Ordinary Importance”: Re
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1942). Ethnological collecting had
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group. More importantly, Murdoch’
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gan to study the question of Indian
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small museums and culture centers i
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fer of Alaskan objects and informat
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fi rst time in polar research— di
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Boas, Franz. 1888a. “The Central
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Lindsay, Debra. 1993. Science in th
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From Tent to Trading Post and Back
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in befriending an extraordinary Inu
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The Smithsonian Institution’s pre
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of departure for research during th
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FIGURE 8. A drawing of the so-calle
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situated experiential education and
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the Past: Archaeologists, Native Am
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Brooding and Species Diversity in t
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iefl y consider below some of the i
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ment. Consequently, the selective e
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ated from the Antarctic. Strong cur
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the four main genera of brooding sc
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ing such cryptic speciation suggest
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LITERATURE CITED Absher, T. M., G.
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Madon-Senez, C. 1998. Disparité Mo
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Persistent Elevated Abundance of Oc
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ABUNDANCE OF ANTARCTIC OCTOPODS 199
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Considerations of Anatomy, Morpholo
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Many theories have been hypothesize
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FIGURE 4. A three dimensional recon
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are wider and more bulbous in the a
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mimicked the shape and profi le of
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faces for SEM observation. The spec
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DISCUSSION Imaging and dissection o
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out its length. The pulp chamber al
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pulpal neurons and dentin tubules.
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Scientifi c Diving Under Ice: A 40-
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TABLE 2. Principal Investigators an
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attaching ice anchors to the chunks
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dumping of weight under water. The
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MARINE LIFE HAZARDS Few polar anima
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Urine should be copious and clear a
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Environmental and Molecular Mechani
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face (�1.8°C) are likely to pose
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FIGURE 2. Illustrated selection shi
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FIGURE 4. Distribution of respirati
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invertebrates were placed in the ba
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Meehan, R. R., D. S. Dunican, A. Ru
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Page 352 and 353: Capital Expenditure and Income (For
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Page 398 and 399: Watching Star Birth from the Antarc
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Page 412 and 413: Index AAUS. See American Academy of
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Page 416 and 417: Fishing. See also Biological invasi
Page 418 and 419: McMurdo Station, xiv, 265-267, 393
Page 420 and 421: Rogick, Mary, 206 Ronne, Finn, 55 R
Page 422: U.S. Naval Support Force Antarctica
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