Radar altimetry of Mercury: A Preliminary analysis

Measurements of Mercurian topography based on Arecibo radar observations are presented. The data, which were obtained from 1978 to 1984, cover much of the equatorial zone of Mercury between 12oN and 5oS latitude. Over thirty continuous altitude profiles were obtained, each spanning from 20 to 90 degrees of longitude at a resolution of 0.15 o (longitude) by 2.5 o (latitude). Radar depths for large craters support previous indications from imagery that Mercurian craters are shallower than lunar craters of the same size. One very large (800 km) impact basin shows some distinct topographic structure, although its relative shallowness suggests postimpact modification by isostatic relaxation or volcanic filling. The plains of Tir Planitia appear topographically smooth to the radar. These plains extend well into the hemisphere not imaged by Mariner 10, possibly forming part of a large annulus of smooth plains around Caloris Basin. The circum-Caloris smooth plains are strongly down-bowed, indicating subsidence under a load. This and other similarities to lunar maria suggest a volcanic origin for these plains. Additional areas of topographically smooth terrain have been found in both the imaged and unimaged hemispheres. Several ridges, scarps, and fault zones have been identified in the altimetry. Three mapped arcuate scarps show heights of about 700 m and cross-sectional widths of about 70 km. One of these features is clearly a ridge, while the other two scarps have a more ridge-like appearance than is suggested by images. One large-scale topographic drop of 3 km correlates well with a mapped system of faults and intracrater scarps. The equatorial zone of Mercury shows 7 km of maximum relief, although the typical elevation difference between highlands and lowlands is closer to 3 km. Three major highland areas are found, the largest two of which are roughly antipodal and aligned within about 10 o of the "hot poles" of Mercury. The unimaged hemisphere, possessing both large craters and topographically smooth areas, does not appear to be markedly different in its topography from the imaged hemisphere. No evidence has been found for another Caloris-type impact structure in the unimaged hemisphere.

[1]  Newell J. Trask,et al.  Preliminary geologic terrain map of Mercury , 1975 .

[2]  J. Head,et al.  Vertical movement in mare basins: Relation to mare emplacement, basin tectonics, and lunar thermal history , 1979 .

[3]  P. Schultz.  Endogenic modification of impact craters on Mercury , 1977 .

[4]  M. Malin,et al.  Modification of fresh crater landforms: Evidence from the Moon and Mercury , 1978 .

[5]  Robert G. Strom,et al.  Tectonism and volcanism on Mercury , 1975 .

[6]  Lionel Wilson,et al.  Photometric observations of Mercury from Mariner 10 , 1975 .

[7]  Kenneth P. Klaasen,et al.  Mercury's rotation axis and period , 1976 .

[8]  Robert G. Strom,et al.  Additional evidence of Mercurian volcanism , 1976 .

[9]  M. E. Strobell,et al.  New Identification of Ancient Multi-Ring Basins on Mercury and Implications for Geologic Evolution , 1984 .

[10]  A E Rogers,et al.  Lunar Topography: Global Determination by Radar: Delay-Doppler stereoscopy and radar interferometry yield high-resolution three-dimensional views of the moon. , 1972, Science.

[11]  M E Davies,et al.  Mercury's Surface: Preliminary Description and Interpretation from Mariner 10 Pictures , 1974, Science.

[12]  Bradford A. Smith,et al.  Cartography of the surface markings of Mercury , 1972 .

[13]  J. Head,et al.  Lunar mascon basins - Lava filling, tectonics, and evolution of the lithosphere , 1980 .

[14]  D. Gault,et al.  Some comparisons of impact craters on Mercury and the Moon , 1975 .

[15]  The Control Net of Mercury , 1976 .

[16]  Don E. Wilhelms,et al.  Mercurian volcanism questioned , 1976 .

[17]  D. H. Scott,et al.  Geologic map of the Kuiper Quadrangle of Mercury , 1981 .

[18]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[19]  Michael C. Malin,et al.  Landform degradation on Mercury, the Moon, and Mars: Evidence from crater depth/diameter relationships , 1977 .

[20]  Merton E. Davies,et al.  Surface Coordinates and Cartography of Mercury. , 1975 .

[21]  Raymond E. Arvidson,et al.  Comparative studies of lunar, Martian, and Mercurian craters and plains , 1977 .

[22]  R. Strom.  Mercury: A post-Mariner 10 assessment , 1979 .

[23]  M. Cintala,et al.  The effects of target characteristics on fresh crater morphology - Preliminary results for the moon and Mercury , 1977 .

[24]  H. Melosh,et al.  Tectonic implications for the gravity structure of Caloris Basin, Mercury , 1978 .

[25]  S. Peale.  Generalized Cassini's laws , 1969 .

[26]  S. Solomon.  Some aspects of core formation in Mercury , 1975 .

[27]  H. J. Melosh,et al.  Mercurian global tectonics - A consequence of tidal despinning , 1978 .

[28]  R. Goldstein,et al.  Surface features on Mercury , 1974 .

[29]  Peter Goldreich,et al.  Spin-orbit coupling in the solar system , 1966 .

[30]  R. P. Ingalls,et al.  Surface‐Height Variations on Venus and Mercury , 1970 .

[31]  J. Boyce,et al.  Moon-Mercury: Large impact structures, isostasy and average crustal viscosity , 1977 .

[32]  Patrick Moore,et al.  The atlas of Mercury , 1977 .

[33]  M. Ash,et al.  The System of Planetary Masses , 1971, Science.

[34]  Richard J. Pike,et al.  Depth/diameter relations of fresh lunar craters: Revision from spacecraft data , 1974 .

[35]  Richard E. Lingenfelter,et al.  Apollo laser altimetry and inferences as to lunar structure , 1974 .

[36]  Daniel Dzurisin,et al.  The tectonic and volcanic history of mercury as inferred from studies of scarps, ridges, troughs, and other lineaments , 1978 .

[37]  P. Esposito,et al.  The occultation of Mariner 10 by Mercury , 1976 .

[38]  G. Schaber,et al.  Geologic map of the Tolstoj Quadrangle of Mercury , 1977 .

[39]  G. Neugebauer,et al.  Mariner 10 infrared radiometer results - Temperatures and thermal properties of the surface of Mercury , 1976 .

[40]  Radar Measurements of Mercury: Topography and Scattering Characteristics at 3.8 CM , 1972 .