[ { "id": "authors:qjkyp-wkk16", "collection": "authors", "collection_id": "qjkyp-wkk16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150408-080531263", "type": "article", "title": "The lakes of Titan", "author": [ { "family_name": "Stofan", "given_name": "E. R.", "clpid": "Stofan-E-R" }, { "family_name": "Elachi", "given_name": "C.", "clpid": "Elachi-C" }, { "family_name": "Muhleman", "given_name": "D.", "clpid": "Muhleman-D-O" } ], "abstract": "The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface1, 2. Initial visible3 and radar4, 5 imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface5, 6. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70\u00b0 north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface2, 7. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.", "doi": "10.1038/nature05438", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2007-01-04", "series_number": "7123", "volume": "445", "issue": "7123", "pages": "61-64" }, { "id": "authors:y2eew-skw59", "collection": "authors", "collection_id": "y2eew-skw59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150318-135538006", "type": "article", "title": "Titan Radar Mapper observations from Cassini's T_3 fly-by", "author": [ { "family_name": "Elachi", "given_name": "C.", "clpid": "Elachi-C" }, { "family_name": "Muhleman", "given_name": "D.", "clpid": "Muhleman-D-O" } ], "abstract": "Cassini's Titan Radar Mapper imaged the surface of Saturn's moon Titan on its February 2005 fly-by (denoted T_3), collecting high-resolution synthetic-aperture radar and larger-scale radiometry and scatterometry data. These data provide the first definitive identification of impact craters on the surface of Titan, networks of fluvial channels and surficial dark streaks that may be longitudinal dunes. Here we describe this great diversity of landforms. We conclude that much of the surface thus far imaged by radar of the haze-shrouded Titan is very young, with persistent geologic activity.", "doi": "10.1038/nature04786", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2006-06-08", "series_number": "7094", "volume": "441", "issue": "7094", "pages": "709-713" }, { "id": "authors:tafvz-x8g95", "collection": "authors", "collection_id": "tafvz-x8g95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141117-150528360", "type": "article", "title": "The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes", "author": [ { "family_name": "Lorenz", "given_name": "R. D.", "orcid": "0000-0001-8528-4644", "clpid": "Lorenz-R-D" }, { "family_name": "Elachi", "given_name": "C.", "clpid": "Elachi-C" }, { "family_name": "Muhleman", "given_name": "D.", "clpid": "Muhleman-D-O" } ], "abstract": "The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show \u223c100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of \u223c0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.", "doi": "10.1126/science.1123257", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2006-05-05", "series_number": "5774", "volume": "312", "issue": "5774", "pages": "724-727" }, { "id": "authors:fqts1-xep19", "collection": "authors", "collection_id": "fqts1-xep19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141114-142403266", "type": "article", "title": "Cassini Radar Views the Surface of Titan", "author": [ { "family_name": "Elachi", "given_name": "C.", "clpid": "Elachi-C" }, { "family_name": "Muhleman", "given_name": "D.", "clpid": "Muhleman-D-O" } ], "abstract": "The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of \u223c0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.", "doi": "10.1126/science.1109919", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2005-05-13", "series_number": "5724", "volume": "308", "issue": "5724", "pages": "970-974" }, { "id": "authors:2pnnn-x3y97", "collection": "authors", "collection_id": "2pnnn-x3y97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111121-090234979", "type": "article", "title": "Mars Orbiter Laser Altimeter: Experiment summary\n after the first year of global mapping of Mars", "author": [ { "family_name": "Smith", "given_name": "David E.", "clpid": "Smith-D-E" }, { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" }, { "family_name": "Ivanov", "given_name": "Anton B.", "clpid": "Ivanov-A-B" } ], "abstract": "The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-\u03bcm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64\u00b0 in latitude \u00d7 1/32\u00b0 in longitude (1 \u00d7 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-\u03bcm reflectivity with an accuracy of 5% have also been obtained.", "doi": "10.1029/2000JE001364", "issn": "0148-0227", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research E", "publication_date": "2001-10-25", "series_number": "E10", "volume": "106", "issue": "E10", "pages": "23689-23722" }, { "id": "authors:r1y9b-04c13", "collection": "authors", "collection_id": "r1y9b-04c13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120914-080828318", "type": "article", "title": "Sublimation from icy jets as a probe of the interstellar\n volatile content of comets", "author": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Qi", "given_name": "C.", "orcid": "0000-0001-8642-1786", "clpid": "Qi-Chunhua" }, { "family_name": "Hogerheijde", "given_name": "Michiel R.", "clpid": "Hogerheidje-M-R" }, { "family_name": "Gurwell", "given_name": "M. A.", "orcid": "0000-0003-0685-3621", "clpid": "Gurwell-M-A" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" } ], "abstract": "Comets are some of the most primitive bodies left over from the Solar System's early history. They may preserve both interstellar material and material from the proto-solar nebula, and so studies of their volatile components can provide clues about the evolution of gases and ices, as a collapsing molecular cloud transforms into a mature planetary system. Previous observations of emission from rotational transitions in molecules have averaged over large areas of the inner coma, and therefore include both molecules that sublimed from the nucleus and those that result from subsequent chemical processes in the coma. Here we present high-resolution observations of emission from the molecules HNC, DCN and HDO associated with comet Hale\u2013Bopp. Our data reveal arc-like structures\u2014icy jets\u2014offset from (but close to) the nucleus. The measured abundance ratios on 1\u20133\" scales are substantially different from those on larger scales, and cannot be accounted for by models of chemical processes in the coma; they are, however, similar to the values observed in the cores of dense interstellar clouds and young stellar objects. We therefore propose that sublimation from millimetre-sized icy grains ejected from the nucleus provides access to relatively unaltered volatiles. The D/H ratios inferred from our data suggest that, by mass, Hale\u2013Bopp (and by inference the outer regions of the early solar nebula) consists of \u226515\u201340% of largely unprocessed interstellar material.", "doi": "10.1038/18372", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "1999-03-18", "series_number": "6724", "volume": "398", "issue": "6724", "pages": "213-216" }, { "id": "authors:dtrsf-t8n10", "collection": "authors", "collection_id": "dtrsf-t8n10", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ROUao97", "type": "article", "title": "Synthesizing radar maps of polar regions with a Doppler-only method", "author": [ { "family_name": "Roulston", "given_name": "Mark S.", "clpid": "Roulston-M-S" }, { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" } ], "abstract": "A method for producing a radar-reflectivity map of the polar regions of the Moon or a planet from polar orbit with only the frequency shift of the reflected signals is described and simulated. A Radon transform of the reflectivity is obtained during multiple passes over the pole. Inversion of this Radon transform enables a map of radar reflectivity to be synthesized.", "issn": "0003-6935", "publisher": "Optical Society of America", "publication": "Applied Optics", "publication_date": "1997-06-10", "series_number": "17", "volume": "36", "issue": "17", "pages": "3912-3919" }, { "id": "authors:eek4b-gn537", "collection": "authors", "collection_id": "eek4b-gn537", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MUHao95", "type": "article", "title": "Microwave spectroscopy of the Mars atmosphere", "author": [ { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Clancy", "given_name": "R. T.", "clpid": "Clancy-R-T" } ], "abstract": "A study of the use of millimeter-wavelength spectral transitions to investigate the atmosphere of Mars is presented. In the model experiments investigated it is assumed that a spectrometer in the frequency range from 100 to 260 GHz looks into a modest-sized telescope of from 30 to 50 cm aperture from a near-Mars orbit. The molecules H2O, CO, O2, O3, and H2O2 all have intense spectral lines in the Mars atmosphere in this frequency range and in addition are all very important in understanding the water cycle, the photochemistry, and the circularization in that atmosphere. It is shown that the altitude and the zonal distribution of H2O can be mapped even in atmospheric columns as dry as 0.25 precipital \u03bcm. Ozone can be mapped over the entire planet, independent of solar-lighting conditions, dust loading, or clouds in the atmosphere, because millimeter waves are insensitive to any particles that can be suspended in the Mars atmosphere. Because the signal-receiving techniques use superheterodyne devices and narrow spectral lines, zonal and meridional winds can be measured at altitudes above 10 km with a precision approaching approximately 3 m/s by the use of Doppler shifts. Temperature\u2013pressure profiles can be measured to altitudes of 100 km by the use of CO lines in the limb-sounding mode.", "issn": "0003-6935", "publisher": "Optical Society of America", "publication": "Applied Optics", "publication_date": "1995-09-20", "series_number": "27", "volume": "34", "issue": "27", "pages": "6067-6080" }, { "id": "authors:mc3cj-pej38", "collection": "authors", "collection_id": "mc3cj-pej38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MUHareps95", "type": "article", "title": "Radar Investigation of Mars, Mercury, and Titan", "author": [ { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" }, { "family_name": "Grossman", "given_name": "Arie W.", "clpid": "Grossman-Arie-W" }, { "family_name": "Butler", "given_name": "Bryan J.", "orcid": "0000-0002-5344-820X", "clpid": "Butler-Bryan-J" } ], "abstract": "Radar astronomy is the study of the surfaces and near surfaces of Solar System objects using active transmission of modulated radio waves and the detection of the reflected energy. The scientific goals of such experiments are surprisingly broad and include the study of surface slopes, fault lines, craters, mountain ranges, and other morphological structures. Electrical reflectivities contain information about surface densities and, to some extent, the chemical composition of the surface layers. Radar probes the subsurface layers to depths of the order of 10 wavelengths, providing geological mapping and determinations of the object's spin state. Radar also allows one to study an object's atmosphere and ionic layers as well as those of the interplanetary medium. Precise measurements of the time delay to surface elements provide topographic maps and powerful information on planetary motions and tests of gravitational theories such as general relativity. In this paper, we limit our discussion to surface and near-surface probing of Mercury, Mars, and Titan and review the work of the past decade, which includes fundamentally new techniques for Earth-based imaging. \n\nThe most primitive experiments involve just the measurement of the total echo power from the object. The most sophisticated experiments would produce spatially resolved maps of the reflected power in all four Stokes' parameters. Historically, the first experiments produced echoes from the Moon during the period shortly after World War II (see e.g. Evans 1962), but the subject did not really develop until the early 1960s when the radio equipment was sufficiently sensitive to detect echoes from Venus and obtain the first Doppler strip \"maps\" of that planet. The first successful planetary radar systems were the Continuous Wave (CW) radar at the Goldstone facility of the Caltech's Jet Propulsion Laboratory and the pulse radar at the MIT Lincoln Laboratory. All of the terrestrial planets were successfully studied during the following decade, yielding the spin states of Venus and Mercury, a precise value of the astronomical unit, and a host of totally new discoveries concerning the surfaces of the terrestrial planets and the Moon. This work opened up at least a similar number of new questions. Although the early work was done at resolution scales on the order of the planetary radii, very rapid increases in system sensitivities improved the resolution to the order of 100 km, but always with map ambiguities. Recently, unambiguous resolution of 100 m over nearly the entire surface of Venus has been achieved from the Magellan spacecraft using a side-looking, synthetic aperture radar. Reviews of the work up to the Magellan era can be found in Evans (1962), Muhleman et al (1965), Evans & Hagfors (1968, see chapters written by G Pettengill, T Hagfors, and J Evans), and Ostro (1993). The radar study of Venus from the Magellan spacecraft was a tour de force and is well described in special issues of Science (volume 252, April 12, 1991) and in the Journal of Geophysical Research (volume 97, August 25 and October 25, 1992). Venus will not be considered in this paper even though important polarization work on that planet continues at Arecibo, Goldstone, and the Very Large Array (VLA). \n\nIn this paper we review the most recent work in Earth-based radar astronomy using new techniques of Earth rotation, super synthesis at the VLA in New Mexico (operated by the National Radio Astronomy Observatory), and the recently developed \"long-code\" techniques at the Arecibo Observatory in Puerto Rico (operated by Cornell University). [Note: It was recently brought to our attention that the VLA software \"doubles\" the flux density of their primary calibrators. Consequently, it is necessary to half the radar power and reflectivity numerical values in all of our published radar results from the VLA/Goldstone radar.] The symbiotic relationship in these new developments for recent advances in our understanding of Mercury and Mars is remarkable. VLA imaging provides for the first time, unambiguous images of an entire hemisphere of a planet and the long-code technique makes it possible to map Mars and Mercury using the traditional range-gated Doppler strip mapping procedure [which was, apparently, developed theoretically at the Lincoln Laboratory by Paul Green, based on a citation in Evans (1962)]. Richard Goldstein was the first to obtain range-gated planetary maps of Venus as reported in Carpenter & Goldstein (1963). Such a system was developed earlier for the Moon as reported by Pettengill (1960) and Pettengill & Henry (1962). We first discuss the synthesis mapping technique.", "doi": "10.1146/annurev.ea.23.050195.002005", "issn": "0084-6597", "publisher": "Annual Review of Earth and Planetary Sciences", "publication": "Annual Review of Earth and Planetary Sciences", "publication_date": "1995-05", "volume": "23", "pages": "337-374" }, { "id": "authors:3fa3b-ht755", "collection": "authors", "collection_id": "3fa3b-ht755", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150122-132953915", "type": "article", "title": "Mercury Radar Imaging: Evidence for Polar Ice", "author": [ { "family_name": "Slade", "given_name": "Martin A.", "clpid": "Slade-M-A" }, { "family_name": "Butler", "given_name": "Bryan J.", "orcid": "0000-0002-5344-820X", "clpid": "Butler-B-J" }, { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" } ], "abstract": "The first unambiguous full-disk radar mapping of Mercury at 3.5-centimeter wavelength, with the Goldstone 70-meter antenna transmitting and 26 antennas of the Very Large Array receiving, has provided evidence for the presence of polar ice. The radar experiments, conducted on 8 and 23 August 1991, were designed to image the half of Mercury not photographed by Mariner 10. The orbital geometry allowed viewing beyond the north pole of Mercury; a highly reflective region was clearly visible on the north pole during both experiments. This polar region has areas in which the circular polarization ratio (pt) was 1.0 to 1.4; values <\u223c0.1 are typical for terrestrial planets. Such high values of have hitherto been observed in radar observations only from icy regions of Mars and icy outer planet satellites.", "doi": "10.1126/science.258.5082.635", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1992-10-23", "series_number": "5082", "volume": "258", "issue": "5082", "pages": "635-640" }, { "id": "authors:zvdg7-eh730", "collection": "authors", "collection_id": "zvdg7-eh730", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150121-151623647", "type": "article", "title": "Radar Images of Mars", "author": [ { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" }, { "family_name": "Butler", "given_name": "Bryan J.", "orcid": "0000-0002-5344-820X", "clpid": "Butler-B-J" }, { "family_name": "Grossman", "given_name": "Arie W.", "clpid": "Grossman-A-W" }, { "family_name": "Slade", "given_name": "Martin A.", "clpid": "Slade-M-A" } ], "abstract": "Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO_2 or H_2O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.", "doi": "10.1126/science.253.5027.1508", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1991-09-27", "series_number": "5027", "volume": "253", "issue": "5027", "pages": "1508-1513" }, { "id": "authors:fx5ak-ewx54", "collection": "authors", "collection_id": "fx5ak-ewx54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150422-083704276", "type": "article", "title": "Radar Reflectivity of Titan", "author": [ { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" }, { "family_name": "Grossman", "given_name": "Arie W.", "clpid": "Grossman-A-W" }, { "family_name": "Butler", "given_name": "Bryan J.", "orcid": "0000-0002-5344-820X", "clpid": "Butler-B-J" }, { "family_name": "Slade", "given_name": "Martin A.", "clpid": "Slade-M-A" } ], "abstract": "The present understanding of the atmosphere and surface conditions on Saturn's largest moon, Titan, including the stability of methane, and an application of thermodynamics leads to a strong prediction of liquid hydrocarbons in an ethane-methane mixture on the surface. Such a surface would have nearly unique microwave reflection properties due to the low dielectric constant. Attempts were made to obtain reflections at a wavelength of 3.5 centimeters by means of a 70-meter antenna in California as the transmitter and the Very Large Array in New Mexico as the receiving instrument. Statistically significant echoes were obtained that show Titan is not covered with a deep, global ocean of ethane, as previously thought. The experiment yielded radar cross sections normalized by the Titan disk of 0.38 \u00b1 0.15, 0.78 \u00b1 0.15, and 0.25 \u00b1 0.15 on three consecutive nights during which the sub-Earth longitude on Titan moved 50 degrees. The result for the combined data for the entire experiment is 0.35 \u00b1 0.08. The cross sections are very high, most consistent with those of the Galilean satellites; no evidence of the putative liquid ethane was seen in the reflection data. A global ocean as shallow as about 200 meters would have exhibited reflectivities smaller by an order of magnitude, and below the detection limit of the experiment. The measured emissivity at similar wavelengths of about 0.9 is somewhat inconsistent with the high reflectivity.", "doi": "10.1126/science.248.4958.975", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1990-05-25", "series_number": "4958", "volume": "248", "issue": "4958", "pages": "975-980" }, { "id": "authors:sp90j-zf002", "collection": "authors", "collection_id": "sp90j-zf002", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150204-145701950", "type": "article", "title": "High-Resolution Microwave Images of Saturn", "author": [ { "family_name": "Grossman", "given_name": "A. W.", "clpid": "Grossman-A-W" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Berge", "given_name": "G. L.", "clpid": "Berge-G-L" } ], "abstract": "An analysis of high-resolution microwave images of Saturn and Saturn's individual rings is presented. Radio interferometric observations of Saturn taken at the Very Large Array in New Mexico at wavelengths of 2 and 6 centimeters reveal interesting new features in both the atmosphere and rings. The resulting maps show an increase in brightness temperature of about 3 K from equator to pole at both wavelengths, while the 6-centimeter map shows a bright band at northern mid-latitudes. The data are consistent with a radiative transfer model of the atmosphere that constrains the well-mixed, fully saturated, NH_3 mixing ratio to be 1.2 x 10^-4 in a region just below the NH_3 clouds, while the observed bright band indicates a 25 percent relative decrease of NH_3 in northern mid-latitudes. Brightness temperatures for the classical rings are presented. Ring brightness shows a variation with azimuth and is linearly polarized at an average value of about 5 percent. The variations in ring polarization suggest that at least 20 percent of the ring brightness is the result of a single scattering process.", "doi": "10.1126/science.245.4923.1211", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1989-09-15", "series_number": "4923", "volume": "245", "issue": "4923", "pages": "1211-1215" }, { "id": "authors:actw2-egd07", "collection": "authors", "collection_id": "actw2-egd07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180720-160139612", "type": "article", "title": "Aperture synthesis observations of Saturn and its rings at 2.7-mm wavelength", "author": [ { "family_name": "Dowling", "given_name": "T. E.", "clpid": "Dowling-T-E" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Berge", "given_name": "G. L.", "clpid": "Berge-G-L" } ], "abstract": "We present 2.7-mm interferometric observations of Saturn made near opposition in June 1984 and June 1985, when the ring opening angle was 19\u00b0 and 23\u00b0, respectively. By combining the data sets we produce brightness maps of Saturn and its rings with a resolution of 6\u2033. The maps show flux from the ring ansae, and are the first direct evidence of ring flux in the 3-mm wavelength region. Modelfits to the visibility data yield a disk brightness temperature of 156 \u00b1 5\u00b0K, a combined A, B, and C ring brightness temperature of 19 \u00b1 3\u00b0K, and a combined a ring cusp (region of the rings which block the planet's disk) brightness temperature of 85 \u00b1 5\u00b0K. These results imply a normal-to-the-ring optical depth for the combined A-B-C ring of 0.31 \u00b1 0.04, which is nearly the same value found for wavelenghts from the UV to 6 cm. About 6\u00b0K of the ring flux is attributed to scattered planetary emission, leaving an intrinsic thermal component of \u223c13\u00b0K. These results, together with the ring particle size distributions found by the Voyager radio occultation experiments, are consistent with the idea that the ring particles are composed chiefly of water ice.", "doi": "10.1016/0019-1035(87)90092-3", "issn": "0019-1035", "publisher": "Elsevier", "publication": "Icarus", "publication_date": "1987-06", "series_number": "3", "volume": "70", "issue": "3", "pages": "505-516" }, { "id": "authors:ez5w2-27m46", "collection": "authors", "collection_id": "ez5w2-27m46", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181211-080024412", "type": "book_section", "title": "Reference Frame Studies at JPL/Caltech", "book_title": "XIXth General Assembly of the IAU", "author": [ { "family_name": "Dickey", "given_name": "J. O.", "clpid": "Dickey-J-O" }, { "family_name": "Esposito", "given_name": "P. B.", "clpid": "Esposito-P-B" }, { "family_name": "Lestrade", "given_name": "J.-F.", "clpid": "Lestrade-J-F" }, { "family_name": "Linfield", "given_name": "R. P.", "clpid": "Linfield-R-P" }, { "family_name": "Melbourne", "given_name": "W. G.", "clpid": "Melbourne-W-G" }, { "family_name": "Newhall", "given_name": "X. X.", "clpid": "Newhall-X-X" }, { "family_name": "Niell", "given_name": "A. E.", "clpid": "Niell-A-E" }, { "family_name": "Preston", "given_name": "R. A.", "clpid": "Preston-R-A" }, { "family_name": "Standish", "given_name": "E. M.", "clpid": "Standish-E-M" }, { "family_name": "Williams", "given_name": "J. G.", "clpid": "Williams-J-G" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Berge", "given_name": "G. L.", "clpid": "Berge-G-L" }, { "family_name": "Rudy", "given_name": "D. J.", "clpid": "Rudy-D-J" } ], "contributor": [ { "family_name": "Swings", "given_name": "Jean-Pierre", "clpid": "Swings-J-P" } ], "abstract": "In recent years, a revolution in astronomical position measurements has been taking place with the advent of modern space techniques. These new techniques, which supplement the traditional astrometric measurements, include laser ranging to the moon and artificial satellites, very-long-baseline interferometry (VLBI) of galactic and extra-galactic radio sources and spacecraft, radio tracking of satellites, and radar-ranging and spacecraft tracking during planetary encounters. Impressive accuracies have been achieved and further improvements are forthcoming. Each technique can be expected to establish its own reference frame which is derived from observations of a particular class of objects. The celestial and terrestrial coordinate systems are related through adopted constants and definitions. Contemporary astronomy has led to the development of three principal celestial coordinate systems: the optical frame (FK4/FK5) based on positions of galactic stars; the planetary/lunar ephemeris frame based on the major celestial bodies of the solar system; and the radio frame constructed from observations of extragalactic radio sources (quasars). Each frame is rotated with respect to others; furthermore, the optical frame offset is time variable. It is important that all frames be interconnected and unified. The optical frame is being connected to the radio frame by VLBI observations of radio emitting stars. The radio frame is being tied to the ephemeris frame in several ways \u2013 one is via differential VLBI measurements between quasars and planet-orbiting spacecraft.", "doi": "10.1017/S1539299600006274", "isbn": "9789027722782", "publisher": "D. Reidel", "place_of_publication": "Dordrecht", "publication_date": "1986", "pages": "93-96" }, { "id": "authors:vttdp-s7d02", "collection": "authors", "collection_id": "vttdp-s7d02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SOLjas85", "type": "article", "title": "Photochemistry and Transport of Carbon Monoxide in the Middle Atmosphere", "author": [ { "family_name": "Solomon", "given_name": "S.", "clpid": "Solomon-S" }, { "family_name": "Garcia", "given_name": "R. R.", "orcid": "0000-0002-6963-4592", "clpid": "Garcia-R-R" }, { "family_name": "Olivero", "given_name": "J. J.", "clpid": "Olivero-J-J" }, { "family_name": "Bevilacqua", "given_name": "R. M.", "clpid": "Bevilacqua-R-M" }, { "family_name": "Schwartz", "given_name": "P. R.", "clpid": "Schwartz-P-R" }, { "family_name": "Clancy", "given_name": "R. T.", "clpid": "Clancy-R-T" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" } ], "abstract": "Two-dimensional model calculations of the photochemistry and transport of carbon monoxide in the stratosphere, mesosphere, and lower thermosphere are presented. Results are compared to available observations at midlatitudes, where both observation and theory suggest that mesospheric CO abundances are larger on average in winter than in summer. The calculations also indicate that extremely large densities of CO should be found in the polar night mesosphere and upper stratosphere, but at present no high-latitude data are available for direct comparison. However, it is suggested that such a latitudinal distribution implies that the midlatitude region can exhibit unusually large abundances of CO under conditions of large-scale planetary wave activity. Two midlatitude observations during late January 1982 am shown to be consistent with this possibility.", "doi": "10.1175/1520-0469(1985)042<1072:PATOCM>2.0.CO;2", "issn": "0022-4928", "publisher": "American Meteorological Society", "publication": "Journal of the Atmospheric Sciences", "publication_date": "1985-05-15", "series_number": "10", "volume": "42", "issue": "10", "pages": "1072-1083" }, { "id": "authors:thg5p-fc183", "collection": "authors", "collection_id": "thg5p-fc183", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150205-151514779", "type": "article", "title": "Microwave Measurements of Carbon Monoxide on Titan", "author": [ { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Berge", "given_name": "G. L.", "clpid": "Berge-G-L" }, { "family_name": "Clancy", "given_name": "R. T.", "clpid": "Clancy-R-T" } ], "abstract": "The ratio of the flux density of Titan was measured in two 200-megahertz bands, one centered on the (1-0) rotation line of carbon monoxide at 115.3 gigahertz and the other 2600 megahertz lower. The measurements were made with a complex-correlation technique on the new millimeter-wavelength interferometer at the Owens Valley Radio Observatory, Big Pine, California. The excess flux in the carbon monoxide band is interpreted as a strong detection of carbon monoxide and a mixing ratio, assumed constant, of 6 x 10^(-5). The brightness temperature of Titan at 112.6 gigahertz is 69 \u00b1 10 kelvins, consistent with atmospheric emission from just below the tropopause.", "doi": "10.1126/science.223.4634.393", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1984-01-27", "series_number": "4634", "volume": "223", "issue": "4634", "pages": "393-396" }, { "id": "authors:q2zba-5k493", "collection": "authors", "collection_id": "q2zba-5k493", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151109-142043082", "type": "article", "title": "Callisto: Disk Temperature at 3.71-Centimeter Wavelength", "author": [ { "family_name": "Berge", "given_name": "Glenn L.", "clpid": "Berge-G-L" }, { "family_name": "Muhleman", "given_name": "Duane O.", "clpid": "Muhleman-D-O" } ], "abstract": "We observed the radio emission of Callisto with a three-element interferometer at the time of the 1973 opposition of Jupiter. Special care was taken to remove the residual, unresolved contribution from Jupiter itself in the antenna side lobes. The resulting disk temperature at a wavelength of 3.71 centimeters, assuming a radius of 2500\u00b175 kilometers for Callisto, was 101\u00b0\u00b125\u00b0K. This temperature is much more consistent with emission from a simple dielectric sphere than the considerably higher temperatures that have been reported for wavelengths of 3.5 and 8.2 millimeters.", "doi": "10.1126/science.187.4175.441", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "1975-02-07", "series_number": "4175", "volume": "187", "issue": "4175", "pages": "441-443" }, { "id": "authors:re2mf-6k662", "collection": "authors", "collection_id": "re2mf-6k662", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150211-123719588", "type": "article", "title": "Principal Scientific Results from the Surveyor Program", "author": [ { "family_name": "Jaffe", "given_name": "L. D.", "clpid": "Jaffe-L-D" }, { "family_name": "Muhleman", "given_name": "D. O.", "clpid": "Muhleman-D-O" }, { "family_name": "Alley", "given_name": "C. O.", "clpid": "Alley-C-O" }, { "family_name": "Norton", "given_name": "R. H.", "clpid": "Norton-R-H" }, { "family_name": "Batterson", "given_name": "S. A.", "clpid": "Batterson-S-A" }, { "family_name": "Scott", "given_name": "R. F.", "clpid": "Scott-R-F" }, { "family_name": "Christensen", "given_name": "E. M.", "clpid": "Christensen-E-M" }, { "family_name": "Shoemaker", "given_name": "E. M.", "clpid": "Shoemaker-E-M" }, { "family_name": "Dwornik", "given_name": "S. E.", "clpid": "Dwornik-S-E" }, { "family_name": "Steinbacher", "given_name": "R. H.", "clpid": "Steinbacher-R-H" }, { "family_name": "Gault", "given_name": "D. E.", "clpid": "Gault-D-E" }, { "family_name": "Sutton", "given_name": "G. H.", "clpid": "Sutton-G-H" }, { "family_name": "Lucas", "given_name": "J. W.", "clpid": "Lucas-J-W" }, { "family_name": "Turkevich", "given_name": "A. L.", "clpid": "Turkevich-A-L" } ], "abstract": "The successful soft landings made by five Surveyors permitted detailed examinations of the lunar surface at four mare sites along an equatorial belt and at one highland\nsite in the southern hemisphere. The aiming areas, selected before launch, were chosen after examination of telescopic and Lunar Orbiter photographs (except for the Surveyor I mission, which preceded the Lunar Orbiter flights). All five spacecraft landed within these selected areas.", "doi": "10.1016/0019-1035(70)90068-0", "issn": "0019-1035", "publisher": "Elsevier", "publication": "Icarus", "publication_date": "1970-03", "series_number": "2", "volume": "12", "issue": "2", "pages": "156-160" } ]