Earth-based 12.6-cm wavelength radar mapping of the Moon: New views of impact melt distribution and mare physical properties

Bruce A. Campbell, Lynn M. Carter, Donald B. Campbell, Michael Nolan, John Chandler, Rebecca R. Ghent, B. Ray Hawke, Ross F. Anderson, Kassandra Wells

Research output: Contribution to journalArticlepeer-review

58 Scopus citations

Abstract

We present results of a campaign to map much of the Moon's near side using the 12.6-cm radar transmitter at Arecibo Observatory and receivers at the Green Bank Telescope. These data have a single-look spatial resolution of about 40. m, with final maps averaged to an 80-m, four-look product to reduce image speckle. Focused processing is used to obtain this high spatial resolution over the entire region illuminated by the Arecibo beam. The transmitted signal is circularly polarized, and we receive reflections in both senses of circular polarization; measurements of receiver thermal noise during periods with no lunar echoes allow well-calibrated estimates of the circular polarization ratio (CPR) and the four-element Stokes vector. Radiometric calibration to values of the backscatter coefficient is ongoing. Radar backscatter data for the Moon provide information on regolith dielectric and physical properties, with particular sensitivity to ilmenite content and surface or buried rocks with diameter of about one-tenth the radar wavelength and larger. Average 12.6-cm circular polarization ratio (CPR) values for low- to moderate-TiO2 mare basalt deposits are similar to those of rough terrestrial lava flows. We attribute these high values to abundant few-centimeter diameter rocks from small impacts and a significant component of subsurface volume scattering. An outflow deposit, inferred to be impact melt, from Glushko crater has CPR values near unity at 12.6-cm and 70-cm wavelengths and thus a very rugged near-surface structure at the decimeter to meter scale. This deposit does not show radar-brightness variations consistent with levees or channels, and appears to nearly overtop a massif, suggesting very rapid emplacement. Deposits of similar morphology and/or radar brightness are noted for craters such as Pythagoras, Rutherfurd, Theophilus, and Aristillus. Images of the north pole show that, despite recording the deposition of Orientale material, Byrd and Peary craters do not have dense patterns of radar-bright ejecta from small craters on their floors. Such patterns in Amundsen crater, near the south pole, were interpreted as diagnostic of abundant impact melt, so the fraction of Orientale-derived melt in the north polar smooth plains, 1000km farther from the basin center, is inferred to be much lower.

Original languageEnglish (US)
Pages (from-to)565-573
Number of pages9
JournalIcarus
Volume208
Issue number2
DOIs
StatePublished - Aug 2010
Externally publishedYes

Keywords

  • Impact processes
  • Moon
  • Volcanism

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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