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Harmon J.K.,National Astronomy and Ionosphere Center | Nolan M.C.,National Astronomy and Ionosphere Center
Icarus | Year: 2017

We conclude our radar imaging survey of Mars, which maps spatial variations in depolarized radar reflectivity using Arecibo S-band (λ12.6 cm) observations from 2005–2012. Whereas our earlier paper (Harmon et al., 2012, Arecibo radar imagery of Mars: the major volcanic provinces. Icarus 220, 990–1030) covered the volcanic regions of Tharsis, Elysium, and Amazonis, this paper includes non-volcanic regions where hydrologic and impact processes can be the dominant resurfacing agents affecting radar backscatter. Many of the more prominent and interesting radar-bright features outside the major volcanic provinces are located in and around Chryse Planitia and Xanthe Terra. These features are identified with: a basin in northeast Lunae Planum containing the combined deposits from Maja Vallis and Ganges Catena outflows; channel outwash plains in western and southern Chryse basin; plateaus bordering chasma/chaos zones, where surface modification may have resulted from hydrologic action associated with incipient chaos formation; and some bright-ejecta craters in Chryse basin, of a type otherwise rare on Mars. Dark-halo craters have also been identified in Chryse and elsewhere that are similar to those seen in the volcanic provinces. Although the cratered highlands are relatively radar-bland, they do exhibit some bright depolarized features; these include eroded crater rims, several unusual ejecta flows and impact melts, and terrain-softened plains. The rims of large impact basins (Hellas, Argyre, Isidis) show a variety of radar-bright features provisionally identified with massif slopes, erosion sediments, eroded pyroclastics, impact melts, and glacial deposits. The interiors of these basins are largely radar-dark, which is consistent with coverage by rock-free sediments. Tempe Terra and Acheron Fossae show bright features possibly associated with rift volcanism or eroded tectonic structures, and northwest Tempe Terra shows one very bright feature associated with glacial or other ice processes in the dichotomy boundary region. The first delay-Doppler images of the radar-bright features from the north and south polar icecaps are presented. Both poles show the circular polarization inversion and high reflectivity characteristic of coherent volume backscatter from relatively clean ice. The south polar feature is primarily backscatter from the residual CO2 icecap (with a lesser contribution from the polar layered deposits), whose finite optical depth probably accounts for the feature's strong S/X-band wavelength dependence. Conversely, the north polar radar feature appears to be mostly backscatter from the H2O-ice-rich polar layered deposits rather than from the thin residual H2O cap. The north polar region shows additional radar-bright features from Korolev Crater and a few other outlying circumpolar ice deposits. © 2016 Elsevier Inc.

The National Astronomical Observatories of China (NAOC) is joining forces with the Breakthrough Initiatives to launch a coordinated search for evidence of intelligent life beyond Earth Using some of the world's most powerful telescopes. NAOC's brand-new FAST telescope - the world's largest filled-aperture radio receiver - will join the Breakthrough Listen program at Green Bank Telescope in the US and the Parkes Observatory in Australia, and together the organization's will exchange observing plans, search methods and data - including the rapid sharing of promising new signals for additional observation and analysis. The two parties are also planning a series of meetings and conferences to refine search strategies, data analyses and results. At a signing ceremony at NAOC headquarters in Beijing, the collaboration was announced via a joint statement by Prof. Jun Yan, Director General of NAOC, and Pete Worden, Chairman of Breakthrough Prize Foundation and Executive Director of Breakthrough Initiatives. They looked forward to "a long and productive scientific collaboration," and invited scientists around the world to join in "one of humanity's greatest quests." "'Are we alone?' is a question that unites us as a planet," said Yuri Milner, Founder of the Breakthrough Initiatives, "And the quest to answer it should take place at a planetary level too. With this agreement, we are now searching for cosmic companions with three of the world's biggest telescopes across three continents." "The Five-hundred-meter Aperture Spherical Telescope (FAST), located in Guizhou, China, achieved first light in September 2016. It is the world's largest filled-aperture radio receiver, and will be one of the most powerful instruments to search for the potential intelligent life beyond Earth," said Prof. Jun Yan, the Director General of NAOC. "We are delighted to be collaborating with the Breakthrough Initiatives." "The FAST telescope is a remarkable instrument with unprecedented power," said Pete Worden, Executive Director of the Breakthrough Initiatives. "We are delighted to be collaborating with NAOC." The Breakthrough Initiatives are a set of long-term astronomical programs exploring the Universe, seeking scientific evidence of life beyond Earth, and encouraging public debate from a planetary perspective. Breakthrough Listen, launched in July 2015, is the most comprehensive astronomical search for intelligent life ever undertaken. It employs two of the world's biggest radio telescopes: the Green Bank Telescope in West Virginia, USA, and the Parkes Observatory in New South Wales, Australia; as well as the Automated Planet Finder at Lick Observatory in California, USA, which searches for laser signals. - Martin Rees, Astronomer Royal, Fellow of Trinity College; Emeritus Professor of Cosmology and Astrophysics, University of Cambridge. - Pete Worden, Chairman, Breakthrough Prize Foundation. - Frank Drake, Chairman Emeritus, SETI Institute; Professor Emeritus of Astronomy and Astrophysics, University of California, Santa Cruz; Founding Director, National Astronomy and Ionosphere Center; Former Goldwin Smith Professor of Astronomy, Cornell University. - Dan Werthimer, Co-founder and chief scientist of the SETI@home project; director of SERENDIP; principal investigator for CASPER. - Andrew Siemion, Director, Berkeley SETI Research Center. For media inquiries: media@breakthroughprize.org OR Rubenstein Communications, Inc. New York, New York Alice McGillion AMcGillion@Rubenstein.com / 212.843.8039

Harmon J.K.,National Astronomy and Ionosphere Center | Slade M.A.,Jet Propulsion Laboratory | Rice M.S.,Cornell University
Icarus | Year: 2011

We present an updated survey of Mercury's putative polar ice deposits, based on high-resolution (1.5-km) imaging with the upgraded Arecibo S-band radar during 1999-2005. The north pole has now been imaged over a full range of longitude aspects, making it possible to distinguish ice-free areas from radar-shadowed areas and thus better map the distribution of radar-bright ice. The new imagery of the south pole, though derived from only a single pair of dates in 2005, improves on the pre-upgrade Arecibo imagery and reveals many additional ice features. Some medium-size craters located within 3° of the north pole show near-complete ice coverage over their floors, central peaks, and southern interior rim walls and little or no ice on their northern rim walls, while one large (90. km) crater at 85°N shows a sharp ice-cutoff line running across its central floor. All of this is consistent with the estimated polar extent of permanent shading from direct sunlight. Some craters show ice in regions that, though permanently shaded, should be too warm to maintain unprotected surface ice owing to indirect heating by reflected and reradiated sunlight. However, the ice distribution in these craters is in good agreement with models invoking insulation by a thin dust mantle. Comparisons with Goldstone X-band radar imagery indicate a wavelength dependence that could be consistent with such a dust mantle. More than a dozen small ice features have been found at latitudes between 67° and 75° All of this low-latitude ice is probably sheltered in or under steep pole-facing crater rim walls, although, since most is located in the Mariner-unimaged hemisphere, confirmation must await imaging by the MESSENGER orbiter. These low-latitude features are concentrated toward the " cold longitudes," possibly indicating a thermal segregation effect governed by indirect heating. The radar imagery places the corrected locations of the north and south poles at 7°W, 88.35°N and 90°W, 88.7°S, respectively, on the original Mariner-based maps. © 2010 Elsevier Inc.

Harmon J.K.,National Astronomy and Ionosphere Center | Nolan M.C.,National Astronomy and Ionosphere Center | Husmann D.I.,National Astronomy and Ionosphere Center | Campbell B.A.,Center for Earth and Planetary Studies
Icarus | Year: 2012

We present Earth-based radar images of Mars obtained with the upgraded Arecibo S-band (λ=12.6 cm) radar during the 2005-2012 oppositions. The imaging was done using the same long-code delay-Doppler technique as for the earlier (pre-upgrade) imaging but at a much higher resolution (~3. km) and, for some regions, a more favorable sub-Earth latitude. This has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity (a proxy for small-scale surface roughness) over the major volcanic provinces of Tharsis, Elysium, and Amazonis. We find that vast portions of these regions are covered by radar-bright lava flows exhibiting circular polarization ratios close to unity, a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces. All of the major volcanoes have radar-bright features on their shields, although the brightness distribution on Olympus Mons is very patchy and the summit plateau of Pavonis Mons is entirely radar-dark. The older minor shields (paterae and tholi) are largely or entirely radar-dark, which is consistent with mantling by dust or pyroclastic material. Other prominent radar-dark features include: the " fan-shaped deposits" , possibly glacial, associated with the three major Tharsis Montes shields; various units of the Medusae Fossae Formation; a region south and west of Biblis Patera where " Stealth" deposits appear to obscure Tharsis flows; and a number of " dark-halo craters" with radar-absorbing ejecta blankets deposited atop surrounding bright flows. Several major bright features in Tharsis are associated with off-shield lava flows; these include the Olympus Mons basal plains, volcanic fields east and south of Pavonis Mons, the Daedalia Planum flows south of Arsia Mons, and a broad expanse of flows extending east from the Tharsis Montes to Echus Chasma. The radar-bright lava plains in Elysium are concentrated mainly in Cerberus and include the fluvio-volcanic channels of Athabasca Valles, Grjotá Valles, and Marte Valles, as well as an enigmatic region at the southern tip of the Cerberus basin. Some of the Cerberus bright features correspond to the distinctive " platy-ridged" flows identified in orbiter images. The radar-bright terrain in Amazonis Planitia comprises two distinct but contiguous sections: a northern section formed of lavas and sediments debouched from Marte Valles and a southern section whose volcanics may derive, in part, from local sources. This South Amazonis region shows perhaps the most complex radar-bright structure on Mars and includes features that correspond to platy-ridged flows similar to those in Cerberus. © 2012 Elsevier Inc..

Chabot N.L.,Johns Hopkins University | Ernst C.M.,Johns Hopkins University | Denevi B.W.,Johns Hopkins University | Harmon J.K.,National Astronomy and Ionosphere Center | And 4 more authors.
Geophysical Research Letters | Year: 2012

Radar-bright features near Mercury's poles have been postulated to be deposits of water ice trapped in cold, permanently shadowed interiors of impact craters. From its orbit about Mercury, MESSENGER repeatedly imaged the planet's south polar region over one Mercury solar day, providing a complete view of the terrain near the south pole and enabling the identification of areas of permanent shadow larger in horizontal extent than approximately 4km. In Mercury's south polar region, all radar-bright features correspond to areas of permanent shadow. Application of previous thermal models suggests that the radar-bright deposits in Mercury's south polar cold traps are in locations consistent with a composition dominated by water ice provided that some manner of insulation, such as a thin layer of regolith, covers many of the deposits. © 2012 by the American Geophysical Union.

Brum C.G.M.,National Astronomy and Ionosphere Center | Tepley C.A.,National Astronomy and Ionosphere Center | Fentzke J.T.,NorthWest Research Associates, Inc. | Fentzke J.T.,Laurel University | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2012

We present a study of the climatology of thermospheric neutral wind (TNW) meridional and zonal components measured with the 630.0nm nightglow Fabry-Perot interferometer at the Arecibo Observatory from 1980 to 2010. We show and discuss the solar and geomagnetic dependencies as well as the long-term trend of the TNW components and their variation over time and season. A main result of this study was the detection of a substantial seasonal and local time dependence of the response of the TNW to solar and geomagnetic activity. In addition, we found that there is a long-term trend in the thermospheric neutral wind, which can be of a larger magnitude than the variation found in the seasonal, solar cycle, and geomagnetic activity influences. A major signature of this trend over the last 30years was an increase in the meridional northward component up to 1.4ms-1yr-1 before midnight local time during the summer.

Goncharenko L.P.,Massachusetts Institute of Technology | Hsu V.W.,University of Colorado at Boulder | Brum C.G.M.,National Astronomy and Ionosphere Center | Zhang S.-R.,Massachusetts Institute of Technology | Fentzke J.T.,Laurel University
Journal of Geophysical Research: Space Physics | Year: 2013

This paper presents a case study of the day-to-day variability in the midlatitude upper atmospheric ion temperature (∼200-400 km) with a focus on variability resulting from meteorological forcing. The data are obtained by the Millstone Hill incoherent scatter radar (42.6°N, 288.5°E) on 18-31 January 2010, in coincidence with a major sudden stratospheric warming. We elucidate oscillations in ion temperature with both tidal periods (∼8 h and ∼12 h) and non-tidal periods (>24 h) by analyzing residuals between the observed temperatures and those expected from an empirical model. We present the spatial-temporal development of periodicities in ion temperature and discuss to what degree these periodicities might be related to the sudden stratospheric warming event. The spectral location and temporal evolution of periodicities with ∼9.9-12.9 h and ∼6.2-7.9 h suggest that they are related to the semidiurnal (12 h) and terdiurnal (8 h) tides that are enhanced during the sudden stratospheric warming. Periodicities with ∼3-4 d and ∼10-13 d are likely related to Rossby waves with 4 d and 10 d periods, while the strong periodicity observed at 16-17 h could result from the nonlinear interaction of the quasi 2 d wave with the semidiurnal tide. As planetary waves are not expected to propagate to altitudes of ∼200-250 km, these experimental results raise questions about the potential mechanisms of coupling between the lower and upper atmosphere. © 2012. American Geophysical Union. All Rights Reserved.

News Article | October 31, 2015
Site: news.yahoo.com

This series of radar images of the asteroid 2015 TB145 were captured by the Arecibo Observatory in Puerto Rico. They show views of the so-called Halloween asteroid as it rotated during a 40-minute observation ahead of its Oct. 31, 2015 flyby of More A huge asteroid the size of the football stadium has a close encounter with Earth today (Oct. 31) and you can watch the space rock safely fly by online this Halloween. NASA scientists have dubbed asteroid a cosmic "Great Pumpkin" to celebrate the spooky holiday flyby. The newfound asteroid 2015 TB145 will buzz Earth 1:01 p.m. EDT (1701 GMT), passing by at a safe range of about 300,000 miles (480,000 kilometers), just beyond the orbit of the moon. The asteroid poses no threat of hitting Earth, but it does give astronomers a tantalizing chance to ping the space rock with radar to learn more about what it's like. Today at 1 p.m. EDT (1700 GMT), the online Slooh Community Observatory will host a free live webcast of asteroid 2015 TB145 to discuss the asteroid's flyby, the "dangers of near-Earth asteroids, the potential fallout of an asteroid this size impacting the Earth or moon and try to understand why it took so long to discover," according to a Slooh statement. You can go to Slooh.com to join and watch this broadcast live, as well as access Slooh's library of past shows. You can also watch the asteroid flyby webcast on Space.com, courtesy of Slooh. The webcast will be hosted by Slooh's Paul Cox and Slooh astronomer Bob Berman. NASA scientists have been tracking asteroid 2015 TB145 with optical telescopes and radar tools since the space rock was discovered on Oct. 10 by astronomers using the University of Hawaii's Pan-STARRS 1 telescope. [Halloween Asteroid Flyby: A Guide for Observers] "We are going to study it with optical, infrared and radar wavelengths," Marina Brozovic, a research scientist with NASA's Jet Propulsion Laboratory in Pasadena, California, said in avideo explaining the asteroid observation plan. The radar images of 2015 TB145 captured during the asteroid's closest approach should offer the best views of the space rock. "We are expecting them to be really spectacular and that they are going to show a wealth of surface features," Brozovic said. So far, observations on Friday (Oct. 30) using the Planetary Radar Group at the National Science Foundation's Arecibo Observatory in Puerto Rico have revealed that the asteroid is about 1,968.5 feet (600 meters) wide, "which is larger than expected," according to a statement from the National Astronomy and Ionosphere Center (NAIC), which runs the observatory. The asteroid also rotates once every five hours, and is hurtling through space at a speed of about 78,293 mph (126,000 km/h), according to the NAIC statement on Facebook. In addition to the Arecibo Observatory, NASA scientists will use the agency's Goldstone Solar System Radar antenna in Goldstone, California to image asteroid 2015 TB145. "The close approach of 2015 TB145 at about 1.3 times the distance of the moon's orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we'll see for several years," JPL scientist Lance Benner, who leads NASA's asteroid radar research program, said in a statement. "We plan to test a new capability to obtain radar images with two-meter resolution for the first time and hope to see unprecedented levels of detail." The Halloween flyby will be the closest approach of an object as large as asteroid 2015 TB145 until 2027, when an asteroid even larger - the 2,600-foot (800 m) object called 1999 AN10 - will pass Earth at a range of 238,000 miles (383,023 km), or about the same distance between the Earth and moon. Copyright 2015 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Mitra D.,National Astronomy and Ionosphere Center | Mitra D.,National Center for Radio Astrophysics | Rankin J.M.,University of Amsterdam | Rankin J.M.,University of Vermont
Astrophysical Journal | Year: 2011

Lyne & Manchester identified a group of some 50 pulsars they called "partial cones" which they found difficult to classify and interpret. They were notable for their asymmetric average profiles and asymmetric polarization position angle (PPA) traverses, wherein the steepest gradient (SG) point fell toward one edge of the total intensity profile. Over the last two decades, this population of pulsars has raised cautions regarding the core/cone model of the radio pulsar emission beam which implies a high degree of order, symmetry, and geometric regularity. In this paper, we reinvestigate this population "partial cone" pulsars on the basis of new single pulse polarimetric observations of 39 of them, observed with the Giant Meterwave Radio Telescope in India and the Arecibo Observatory in Puerto Rico. These highly sensitive observations help us to establish that most of these "partial cones" exhibit a core/cone structure just as did the "normal" pulsars studied in the earlier papers of this series. In short, we find that many of these "partial cones" are partial in the sense that the emission above different areas of their polar caps can be (highly) asymmetric. However, when studied closely we find that their emission geometries are overall identical to a core/double cone structure encountered earlier-that is, with specific conal dimensions scaling as the polar cap size. Further, the "partial cone" population includes a number of stars with conal single profiles that are asymmetric at meter wavelengths for unknown reasons (e.g., like those of B0809+74 or B0943+10). We find that aberration-retardation appears to play a role in distorting the core/cone emission-beam structure in rapidly rotating pulsars. We also find several additional examples of highly polarized pre-and postcursor features that do not appear to be generated at low altitude but rather at high altitude, far from the usual polar flux tube emission sites of the core and conal radiation. © 2011. The American Astronomical Society.

Harmon J.K.,National Astronomy and Ionosphere Center | Nolan M.C.,National Astronomy and Ionosphere Center | Giorgini J.D.,Jet Propulsion Laboratory | Howell E.S.,National Astronomy and Ionosphere Center
Icarus | Year: 2010

Arecibo radar imagery of Comet 8P/Tuttle reveals a 10-km-long nucleus with a highly bifurcated shape consistent with a contact binary. A separate echo component was also detected from large (>cm-size), slow-moving grains of the type expected to contribute to the Ursid meteor stream. © 2009 Elsevier Inc. All rights reserved.

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