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Abstract
Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 +/- 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 +/- 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is decoupled from a core that is at least partially molten.
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Affiliation(s)
- J L Margot
- Department of Astronomy, Cornell University, 304 Space Sciences Building, Ithaca, NY 14853, USA.
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2
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Scheeres DJ, Fahnestock EG, Ostro SJ, Margot JL, Benner LAM, Broschart SB, Bellerose J, Giorgini JD, Nolan MC, Magri C, Pravec P, Scheirich P, Rose R, Jurgens RF, De Jong EM, Suzuki S. Dynamical configuration of binary near-Earth asteroid (66391) 1999 KW4. Science 2006; 314:1280-3. [PMID: 17038588 DOI: 10.1126/science.1133599] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Dynamical simulations of the coupled rotational and orbital dynamics of binary near-Earth asteroid 66391 (1999 KW4) suggest that it is excited as a result of perturbations from the Sun during perihelion passages. Excitation of the mutual orbit will stimulate complex fluctuations in the orbit and rotation of both components, inducing the attitude of the smaller component to have large variation within some orbits and to hardly vary within others. The primary's proximity to its rotational stability limit suggests an origin from spin-up and disruption of a loosely bound precursor within the past million years.
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Affiliation(s)
- D J Scheeres
- Department of Aerospace Engineering, University of Michigan, 1320 Beal Avenue, Ann Arbor, MI 48109-2140, USA.
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3
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Margot JL, Nolan MC, Benner LAM, Ostro SJ, Jurgens RF, Giorgini JD, Slade MA, Campbell DB. Binary asteroids in the near-Earth object population. Science 2002; 296:1445-8. [PMID: 11951001 DOI: 10.1126/science.1072094] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Radar images of near-Earth asteroid 2000 DP107 show that it is composed of an approximately 800-meter-diameter primary and an approximately 300-meter-diameter secondary revolving around their common center of mass. The orbital period of 1.755 +/- 0.007 days and semimajor axis of 2620 +/- 160 meters constrain the total mass of the system to 4.6 +/- 0.5 x 10(11) kilograms and the bulk density of the primary to 1.7 +/- 1.1 grams per cubic centimeter. This system and other binary near-Earth asteroids have spheroidal primaries spinning near the breakup point for strengthless bodies, suggesting that the binaries formed by spin-up and fission, probably as a result of tidal disruption during close planetary encounters. About 16% of near-Earth asteroids larger than 200 meters in diameter may be binary systems.
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Affiliation(s)
- J L Margot
- California Institute of Technology, MC 150-21, Pasadena, CA 91125, USA.
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4
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Giorgini JD, Ostro SJ, Benner LAM, Chodas PW, Chesley SR, Hudson RS, Nolan MC, Klemola AR, Standish EM, Jurgens RF, Rose R, Chamberlin AB, Yeomans DK, Margot JL. Asteroid 1950 DA's encounter with Earth in 2880: physical limits of collision probability prediction. Science 2002; 296:132-6. [PMID: 11935024 DOI: 10.1126/science.1068191] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft.
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Affiliation(s)
- J D Giorgini
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA.
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5
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Ostro SJ, Pravec P, Benner LA, Hudson RS, Sarounova L, Hicks MD, Rabinowitz DL, Scotti JV, Tholen DJ, Wolf M, Jurgens RF, Thomas ML, Giorgini JD, Chodas PW, Yeomans DK, Rose R, Frye R, Rosema KD, Winkler R, Slade MA. Radar and optical observations of asteroid 1998 KY26. Science 1999; 285:557-60. [PMID: 10417379 DOI: 10.1126/science.285.5427.557] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Observations of near-Earth asteroid 1998 KY26 shortly after its discovery reveal a slightly elongated spheroid with a diameter of about 30 meters, a composition analogous to carbonaceous chondritic meteorites, and a rotation period of 10.7 minutes, which is an order of magnitude shorter than that measured for any other solar system object. The rotation is too rapid for 1998 KY26 to consist of multiple components bound together just by their mutual gravitational attraction. This monolithic object probably is a fragment derived from cratering or collisional destruction of a much larger asteroid.
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Affiliation(s)
- SJ Ostro
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA. Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-25165 Ond&rbreve;ejov, Czech Republic. School of Electrical Engineering and
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6
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Abstract
Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively.
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Affiliation(s)
- J L Margot
- Department of Astronomy, Space Sciences Building, Cornell University, Ithaca, NY 14853, USA
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7
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Harmon JK, Ostro SJ, Benner LAM, Rosema KD, Jurgens RF, Winkler R, Yeomans DK, Choate D, Cormier R, Giorgini JD, Mitchell DL, Chodas PW, Rose R, Kelley D, Slade MA, Thomas ML. Radar detection of the nucleus and coma of comet hyakutake. Science 1997; 278:1921-4. [PMID: 9395389 DOI: 10.1126/science.278.5345.1921] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Radar observations of comet Hyakutake (C/1996 B2) made at the Goldstone Deep Space Communications Complex in California have detected echoes from the nucleus and from large grains in the inner coma. The nucleus of this bright comet was estimated to be only 2 to 3 kilometers in diameter. Models of the coma echo indicate backscatter from porous, centimeter-size grains ejected anisotropically at velocities of tens of meters per second. The radar observations suggest that a comet's activity may be a poor indicator of its size and provide evidence that large grains constitute an important component of the mass loss from a typical active comet.
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Affiliation(s)
- JK Harmon
- J. K. Harmon, National Astronomy and Ionosphere Center, Arecibo Observatory, Post Office Box 995, Arecibo, PR 00614, USA. S. J. Ostro, L. A. M. Benner, K. D. Rosema, R. F. Jurgens, R. Winkler, D. K. Yeomans, D. Choate, R. Cormier, J. D. Giorg
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Haldemann AFC, Mitchell DL, Jurgens RF, Slade MA, Muhleman DO. Mars Pathfinder landing site assessment with Goldstone delay-Doppler and CW radar experiments. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/96je03321] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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9
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Abstract
Radar echoes from the martian satellite Phobos provide information about that object's surface properties at scales near the 3.5-cm observing wavelength. Phobos appears less rough than the moon at centimeter-to-decimeter scales. The uppermost few decimeters of the satellite's regolith have a mean bulk density within 20% of 2.0 g cm(-3). The radar signature of Phobos (albedo, polarization ratio, and echo spectral shape) differs from signatures measured for small, Earth-approaching objects, but resembles those of large (>/=100-km), C-class, mainbelt asteroids.
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10
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Abstract
Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas.
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12
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Abstract
A radar interferometer was used to map unambiguously the surface reflectivity of Venus in the polarized mode at a wavelength of 70 centimeters. The observed region extended from 260 degrees to 30 degrees in longitude and from -60 degrees to 50 degrees in latitude with a surface resolution of approximately 3 degrees by 3 degrees . The result agrees well in most respects with earlier maps made elsewhere at shorter wavelengths and, in addition, discloses a number of new "features."
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13
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Abstract
Spectrum analysis of radar waves backscattered from an anulus near the limb of Venus shows that a uniform scattering model applies over regions extending from the equator to within approximately 15 degrees of the poles. These observations indicate that large polar ice caps extending to latitudes as low as 60 degrees are very unlikely.
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