Radar Observations of Asteroid 216 Kleopatra Ostro, Steven J.; Hudson, R. Scott; Nolan, Michael C. ...
Science (American Association for the Advancement of Science),
05/2000, Letnik:
288, Številka:
5467
Journal Article
Recenzirano
Radar observations of the main-belt, M-class asteroid 216 Kleopatra reveal a dumbbell-shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers (±25%). The asteroid's ...surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil. Kleopatra's shape is probably the outcome of an exotic sequence of collisional events, and much of its interior may have an unconsolidated rubble-pile structure.
•We observed Asteroid 2003 MS2 with radar with 19m resolution.•The dimensions of 2003 MS2 are 0.33×0.19km.•A circular polarization ratio of 0.30 is comparable to 25143 Itokawa suggesting a similar ...degree of near-surface roughness.•The interval of orbit reliability increased with the radar and optical astrometry to 1564–2320.
We report radar observations of near-Earth Asteroid (NEA) 2003 MS2 with Goldstone (8560MHz, 3.5cm) on June 28, 29, and July 4, 2003, shortly after the asteroid’s discovery. Delay-Doppler images with resolutions as fine as 19m/pixel reveal an unusually angular object with pronounced facets. The longest sequence of images was obtained on July 4 when the asteroid rotated ∼140deg in 2.7h. During this interval, bandwidths varied by a factor of ∼1.5 and indicate that 2003 MS2 is an elongated object. The rotation and bandwidth variations evident in the radar images are consistent with the 7h rotation period and the 0.7 magnitude lightcurve amplitude reported by Muinonen et al. (Muinonen, K. et al. 2007. Spins, shapes, and orbits for near-Earth objects by Nordic NEON. In: Milani, A., Valsecchi, G.B., Vokrouhlický, D. (Eds.), Near Earth Objects, our Celestial Neighbors: Opportunity and Risk. Cambridge University Press, Cambridge, pp. 309–320). If we adopt the 7h period, then the maximum and minimum bandwidths place lower bounds on the pole-on dimensions of (0.33×0.19)km/cosδ, where δ is the unknown subradar latitude. The radar and photometric observations by Muinonen et al. constrain the pole directions to (λ, β)=(20±20deg, 0±40deg) and (200±20deg, 0±40deg). The circular polarization ratio of 0.31±0.02 is comparable to that of 25143 Itokawa, suggesting a similar degree of near-surface roughness at decimeter spatial scales.
As NASA and other space agencies are gearing up to return to the moon, there is significant interest and opportunities in detecting and tracking small objects, both man-made and otherwise, in ...cis-lunar space, a vast void between terrestrial orbits and the moon. This paper investigates the feasibility and performance of using NASA's Deep Space Network (DSN) tracking stations and the Goldstone Solar System Radar (GSSR), currently the world's most capable planetary radar transmitter, to detect and track Cis-Lunar targets. In 2022, the JPL GSSR team performed three Cis-Lunar radar experiments using DSN Open Loop Recorders (OLRs). Observations were made by illuminating the targets with continuous waveform (CW) and Pseudo Random Noise (PRN) codes at X-band with the 450kW transmitter on DSS-14, a 70-m diameter antenna at Goldstone, and detecting the targets' reflection echoes at DSS-13, DSN's 34-m diameter R&D antenna in Goldstone, CA, using an open-loop recording system. We evaluate the performance of Cis-Lunar target detection by comparing observations with the Doppler frequency estimates derived from spacecraft's orbital dynamics, lunar noise temperature impacts, Moon clutter effects, and Signal-to-Noise Ratio simulations. This investigation will improve our understanding of engineering and science constraints for future detection and tracking of Cis-Lunar targets, including satellites, debris, asteroids, and surface assets on the moon.
We report Arecibo observations of 55 main-belt asteroids (MBAs) during 1999–2003. Most of our targets had not been detected previously with radar, so these observations more than double the number of ...radar-detected MBAs. Our bandwidth estimates constrain our targets' pole directions in a manner that is geometrically distinct from optically derived constraints. We present detailed statistical analyses of the disk-integrated properties (radar albedo and circular polarization ratio) of the 84 MBAs observed with radar through March 2003; all of these observations are summarized in the online supplementary information. Certain conclusions reached in previous studies are strengthened: M asteroids have higher mean radar albedos and a wider range of albedos than do other MBAs, suggesting that both metal-rich and metal-poor M-class objects exist; and C- and S-class MBAs have indistinguishable radar albedo distributions, suggesting that most S-class objects are chondritic. Also in accord with earlier results, there is evidence that primitive asteroids from outside the C taxon (F, G, P, and D) are not as radar-bright as C and S objects, but a convincing statistical test must await larger sample sizes. In contrast with earlier work, we find S-class MBAs to have higher circular polarization ratios than other MBAs, indicating greater near-surface structural complexity at decimeter scales, due to different mineralogy (material strength or loss tangent), a different impactor population, or both.
A radar survey of M- and X-class asteroids Shepard, Michael K.; Clark, Beth Ellen; Nolan, Michael C. ...
Icarus (New York, N.Y. 1962),
05/2008, Letnik:
195, Številka:
1
Journal Article
Recenzirano
We observed ten M- and X-class main-belt asteroids with the Arecibo Observatory's S-band (12.6 cm) radar. The X-class asteroids were targeted based on their albedos or other properties which ...suggested they might be M-class. This work brings the total number of main-belt M-class asteroids observed with radar to 14. We find that three of these asteroids have rotation rates significantly different from what was previously reported. Based on their high radar albedo, we find that only four of the fourteen—16 Psyche, 216 Kleopatra, 758 Mancunia, and 785 Zwetana—are almost certainly metallic. 129 Antigone has a moderately high radar albedo and we suggest it may be a CH/CB/Bencubbinite parent body. Three other asteroids, 97 Klotho, 224 Oceana, and 796 Sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them. Five of our target asteroids, 16 Psyche, 129 Antigone, 135 Hertha, 758 Mancunia, and 785 Zwetana, show variations in their radar albedo with rotation. We can rule out shape and composition in most cases, leaving variations in thickness, porosity, or surface roughness of the regolith to be the most likely causes. With the exception of 129 Antigone, we find no hydrated M-class asteroids (W-class; Rivkin, A.S., Howell, E.S., Lebofsky, L.A., Clark, B.E., Britt, D.T., 2000. Icarus 145, 351–368) to have high radar albedos.
Abstract We report radar, photometric, and visible-wavelength spectrophotometry observations of NEA 2018 EB obtained in 2018. The radar campaign started at Goldstone (8560 MHz, 3.5 cm) on April 7, ...and it was followed by more extensive observations from October 5 to 9 by both Arecibo (2380 MHz, 12.6 cm) and Goldstone. 2018 EB was observed optically on April 5, 8, and 9 and again on October 18. Spectrophotometry was obtained on October 19 with the SOAR telescope, and the data suggest that 2018 EB is an Xk-class object. The echo power spectra and delay-Doppler radar images revealed that 2018 EB is a binary system. Radar images constrained the satellite's diameter to 0.15 − 0.05 + 0.02 km, but the data were not sufficient for shape modeling. Shape modeling of lightcurves and radar data yielded an oblate primary with an effective diameter D = 0.30 ± 0.04 km and a sidereal rotation period of 4.3 − 0.5 + 0.6 hr. Measurements of delay-Doppler separations between the centers of mass of the primary and the satellite, along with the timing of a radar eclipse observed on October 9, resulted in an orbit fit for the satellite with a semimajor axis of 0.50 − 0.01 + 0.04 km, an eccentricity of 0.15 ± 0.04, a period of 16.85 − 0.26 + 0.33 hr, and an orbit pole constrained to the ecliptic longitudes and latitudes of λ = 93 − 43 ° + 27 ° and β = 48 − 18 ° + 7 ° . The system mass was estimated to be 2.03 − 0.08 + 0.52 × 10 10 kg, which yielded a bulk density of 1.4 − 0.5 + 0.6 g cm −3 . Our analysis suggests that 2018 EB has a low optical albedo of p V = 0.028 ± 0.016 and a relatively high radar albedo of η OC = 0.29 ± 0.11 at Arecibo and η = 0.22 ± 0.10 at Goldstone.
2023 DZ2 Planetary Defense Campaign Reddy, Vishnu; Kelley, Michael S.; Benner, Lance ...
The planetary science journal,
06/2024, Letnik:
5, Številka:
6
Journal Article, Web Resource
Recenzirano
Odprti dostop
Abstract We present the results of a fourth planetary defense exercise, focused this time on the small near-Earth asteroid (NEA) 2023 DZ2 and conducted during its close approach to the Earth in 2023 ...March. The International Asteroid Warning Network (IAWN), with support from NASA's Planetary Defense Coordination Office (PDCO), has been coordinating planetary defense observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. The last campaign focused on the NEA Apophis, and an outcome of that exercise was the need for a short burst campaign to replicate a real-life near-Earth object impact hazard scenario. The goal of the 2023 DZ2 campaign was to characterize the small NEA as a potential impactor and exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication with a short notice of just 24 hr. The entire campaign lasted about 10 days. The campaign team was divided into several working groups based on the characterization method: photometry, spectroscopy, thermal IR photometry and optical polarimetry, radar, and risk assessment. Science results from the campaign show that 2023 DZ2 has a rotation period of 6.2745 ± 0.0030 minutes; visible wavelength color photometry/spectroscopy/polarimetry and near-IR spectroscopy all point to an E-type taxonomic classification with surface composition analogous to aubrite meteorites; and radar observations show that the object has a diameter of 30 ± 10 m, consistent with the high albedo (0.49) derived from polarimetric and thermal IR observations.
Near-Earth Asteroid (29075) 1950 DA may closely encounter Earth in 2880. The probability of Earth impact may be as high as 1/300, but the outcome of the encounter depends critically on the physical ...properties of the asteroid Giorgini et al., 2002. Science 196, 132–136. We have used Arecibo and Goldstone radar data and optical lightcurves to estimate the shape, spin state, and surface structure of 1950 DA. The data allow two distinct models. One rotates prograde and is roughly spheroidal with mean diameter
1.16
±
0.12
km
. The other rotates retrograde and is oblate and about 30% larger. Both models suggest a nickel–iron or enstatite chondritic composition. Ground-based observations should be able to determine which model is correct within the next several decades.
Abstract On 2020 April 29, the near-Earth object (52768) 1998 OR2 experienced a close approach to Earth at a distance of 16.4 lunar distances (LD). 1998 OR2 is a potentially hazardous asteroid of ...absolute magnitude H = 16.04 that can currently come as close to Earth as 3.4 LD. We report here observations of this object in polarimetry, photometry, and radar. Our observations show that the physical characteristics of 1998 OR2 are similar to those of both M- and S-type asteroids. Arecibo’s radar observations provide a high radar albedo of σ ˆ OC = 0.29 ± 0.08, suggesting that metals are present in 1998 OR2 near-surface. We find a circular polarization ratio of μ c = 0.291 ± 0.012, and the delay-Doppler images show that the surface of 1998 OR2 is a top-shape asteroid with large-scale structures such as large craters and concavities. The polarimetric observations display a consistent variation of the polarimetric response as a function of the rotational phase, suggesting that the surface of 1998 OR2 is heterogeneous. Color observations suggest an X-complex taxonomy in the Bus–DeMeo classification. Combining optical polarization, radar, and two epochs from the NEOWISE satellite observations, we derived an equivalent diameter of D = 1.80 ± 0.1 km and a visual albedo p v = 0.21 ± 0.02. Photometric and radar data provide a sidereal rotation period of P = 4.10872 ± 0.00001 hr, a pole orientation of (332.°3 ± 5°, 20.°7 ± 5°), and a shape model with dimensions of ( 2.08 − 0.10 + 0.10 , 1.93 − 0.10 + 0.10 , 1.60 − 0.05 + 0.05 ) km.
► (8567) 1996 HW1 is a contact binary near-Earth asteroid. ► (8567) 1996 HW1 is a highly elongated near-Earth asteroid. ► (8567) 1996 HW1 could have originated as a binary asteroid system.
We ...observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008–2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8
×
1.6
×
1.5
km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243
±
0.00004
h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the
a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.
