Planetary radar astronomy

Ostro, S. J.

doi:10.1103/revmodphys.65.1235

Cited by 233 publications

(114 citation statements)

References 210 publications

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“…In particular, the radar circular polarisation ratio is sensitive to surface roughness at spatial scales that range upwards from the radar wavelength (Ostro 1993). For near-Earth asteroids (4179) Toutatis and (25143) Itokawa (Nolan et al 2013), their 3.5-cm circular polarisation ratios (i.e.…”

Section: Geological Interpretation Of Surface Roughness Derived By Thmentioning

confidence: 99%

The surface roughness of (433) Eros as measured by thermal-infrared beaming

Rozitis

2016

Mon. Not. R. Astron. Soc.

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In planetary science, surface roughness is regarded to be a measure of surface irregularity at small spatial scales, and causes the thermal-infrared beaming effect (i.e. re-radiation of absorbed sunlight back towards to the Sun). Typically, surface roughness exhibits a degeneracy with thermal inertia when thermophysical models are fitted to disc-integrated thermal-infrared observations of asteroids because of this effect. In this work, it is demonstrated how surface roughness can be constrained for near-Earth asteroid (433) Eros (i.e. the target of NASA's NEAR Shoemaker mission) when using the Advanced Thermophysical Model with thermal-infrared observations taken during an "almost poleon" illumination and viewing geometry. It is found that the surface roughness of (433) Eros is characterised by an RMS slope of 38 ± 8° at the 0.5-cm spatial scale associated with its thermalinfrared beaming effect. This is slightly greater than the RMS slope of 25 ± 5° implied by the NEAR Shoemaker laser ranging results when extrapolated to this spatial scale, and indicates that other surface shaping processes might operate, in addition to collisions and gravity, at spatial scales under one metre in order to make asteroid surfaces rougher. For other high obliquity asteroids observed during "pole-on" illumination conditions, the thermal-infrared beaming effect allows surface roughness to be constrained when the sub-solar latitude is greater than 60°, and if the asteroids are observed at phase angles of less than 40°. They will likely exhibit NEATM beaming parameters that are lower than expected for a typical asteroid at all phase angles up to 100°.

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Section: Geological Interpretation Of Surface Roughness Derived By Thmentioning

confidence: 99%

The surface roughness of (433) Eros as measured by thermal-infrared beaming

Rozitis

2016

Mon. Not. R. Astron. Soc.

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“…Ostro (1989) summarized the early efforts to study the shapes and outer contours of NEAs. The two planetary radar facilities, Arecibo Observatory and Goldstone Deep Space Network, are complementary in their capabilities and ability to study solid solar system bodies, primarily NEAs (Ostro et al, 2002 and references therein).…”

Section: Structure Of Asteroidsmentioning

confidence: 99%

Asteroids and Comets

Fernández¹,

Li²,

Howell³

et al. 2015

Treatise on Geophysics

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Asteroids and comets are remnants from the era of Solar System formation over 4.5 billion years ago, and therefore allow us to address two fundamental questions in astronomy: what was the nature of our protoplanetary disk, and how did the process of planetary accretion occur? The objects we see today have suffered many geophysically-relevant processes in the intervening eons that have altered their surfaces, interiors, and compositions. In this chapter we review our understanding of the origins and evolution of these bodies, discuss the wealth of science returned from spacecraft missions, and motivate important questions to be addressed in the future.Comment: 84 pages, 27 figures. To be published in Treatise on Geophysics, 2nd edition (G. Schubert, Editor-in-Chief), Volume 10 (T. Spohn, Editor

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“…with k B Boltzmann's constant, T sys the system temperature, Δf the frequency resolution, and τ the integration time (Ostro 1993;Naidu et al 2016). The power received by a transmitter of power P t and antenna gain G t located at distance r is…”

Section: Sensitivitymentioning

confidence: 99%

A Search for Technosignatures from 14 Planetary Systems in the Kepler Field with the Green Bank Telescope at 1.15–1.73 GHz

Margot¹,

Greenberg²,

Pinchuk³

et al. 2018

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Analysis of Kepler mission data suggests that the Milky Way includes billions of Earth-sized planets in the habitable zone of their host stars. Current technology enables the detection of technosignatures emitted from a large fraction of the Galaxy. We describe a search for technosignatures that is sensitive to Arecibo-class transmitters located within ∼420 ly of Earth and transmitters that are 1000 times more effective than Arecibo within ∼13000 ly of Earth. Our observations focused on 14 planetary systems in the Kepler field and used the L-band receiver (1.15-1.73 GHz) of the 100m diameter Green Bank Telescope. Each source was observed for a total integration time of 5 minutes. We obtained power spectra at a frequency resolution of 3Hz and examined narrowband signals with Doppler drift rates between±9Hzs −1 . We flagged any detection with a signal-to-noise ratio in excess of 10 as a candidate signal and identified approximately 850,000 candidates. Most (99%) of these candidate signals were automatically classified as human-generated radio-frequency interference (RFI). A large fraction (>99%) of the remaining candidate signals were also flagged as anthropogenic RFI because they have frequencies that overlap those used by global navigation satellite systems, satellite downlinks, or other interferers detected in heavily polluted regions of the spectrum. All 19 remaining candidate signals were scrutinized and none were attributable to an extraterrestrial source.

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Planetary radar astronomy

Cited by 233 publications

References 210 publications

The surface roughness of (433) Eros as measured by thermal-infrared beaming

The surface roughness of (433) Eros as measured by thermal-infrared beaming

Asteroids and Comets

A Search for Technosignatures from 14 Planetary Systems in the Kepler Field with the Green Bank Telescope at 1.15–1.73 GHz

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