From baalke@kelvin.jpl.nasa.gov Mon Mar 29 20:15:49 1993 Status: RO X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["7328" "" "30" "March" "1993" "00:34" "UT" "Ron Baalke" "baalke@kelvin.jpl.nasa.gov " nil "127" "Magellan Venus Maps" "^From:" nil nil "3"]) Newsgroups: sci.space,sci.astro,alt.sci.planetary Organization: Jet Propulsion Laboratory Distribution: world NNTP-Posting-Host: kelvin.jpl.nasa.gov Keywords: Magellan, MIT, JPL News-Software: VAX/VMS VNEWS 1.41 From: baalke@kelvin.jpl.nasa.gov (Ron Baalke) Subject: Magellan Venus Maps Date: 30 Mar 1993 00:34 UT ========================== Magellan Venus Maps March 29, 1993 ========================== Three more Magellan Venus maps are now available in GIF and JPEG formats. These maps are courtesy of Peter Ford from MIT, working on the Magellan Project. They were made from the altimeter and radiometer data from all 3 Magellan radar mapping cycles (24 months of operation). The maps are shown in Mercator projection for the regions of the planet between 69 degrees north and 69 degrees south latitude, and in stereographic projections for the polar regions. The images have been anti-aliased in order to make their embedded text readable, and have been reduced to 820x820 pixel, 256 color resolution. Caption files accompanying the images are also included. The images are available using anonymous ftp to: ftp: ames.arc.nasa.gov (128.102.18.3) user: anonymous cd: pub/SPACE/GIF files: gedrp3v2.gif (Microwave Emissivity Map) gedrp3v2.txt gsdrp3v2.gif (Average Meter-Scale Slope Map) gsdrp3v2.txt gtdrp3v2.gif (Topography Map) gtdrp3v2.txt cd: pub/SPACE/JPEG files: gedrp3v2.jpg (Microwave Emissivity Map) gedrp3v2.txt gsdrp3v2.jpg (Average Meter-Scale Slope Map) gsdrp3v2.txt gtdrp3v2.jpg (Topography Map) gtdrp3v2.txt --------------------------------------------------------------------- gedrp3v2.txt These maps of Venus show how well various regions of the surface radiate heat compared to a perfect radiator. They display in color a quantity called emissivity, observed using a Magellan Synthetic Aperture Radar (SAR) receiver during its 24 months of systematic mapping in Venus orbit. Color is used to code the emission efficiency (see color bar). Red corresponds to the highest, blue to the lowest values of emissivity. The upper image shows the portion of the planet between 69 degrees north and 69 degrees south latitude in Mercator projection; beneath it are the two polar regions covering latitudes above 44 degrees in stereographic projection. The horizontal resolution varies with latitude, being determined solely by the "footprint" of Magellan's high-gain SAR antenna beam. Near the equator the surface resolution is about 20 kilometers (12.4 miles) but at high latitudes it degrades to as much as 100 kilometers (62 miles). Emissivity of the surface is a measure of how well the surface radiates heat. Higher regions, such as the Maxwell Montes (at top left center) and Aphrodite Terra (along the equator at right center), usually show lower values of emissivity than are typical of lower-lying areas. On a cooler planet, such as Earth or Mars, water or ice might explain the puzzling observations but at the surface temperature of Venus -- 470 degrees C (878 F) -- neither can be present. Some theories call for the presence of an electrically-conducting mineral such as pyrite (the minerals have an electrical field when illuminated by radar); others suggest a material as yet unidentified that has an extremely low electrical loss. The data shown here were compiled and analyzed at the Center for Space Research, Massachusetts Institute of Technology. --------------------------------------------------------------------- gsdrp3v2.txt These images display the meter-scale roughness of the Venus surface (characterized by its root-mean-square average slope), as observed by the Magellan radar altimeter during its 24 months of systematic mapping. The lightest shades locate areas having the highest values of roughness, while darker shades indicate areas that are smoother. The upper image shows that part of the planet between 69 degrees north and 69 degrees south latitude in Mercator projection; beneath it are the two polar regions covering latitudes above 44 degrees in stereographic projection. Easterly longitudes run across the Mercator map from left to right, and around the periphery of the polar stereographic projections. Resolution of the surface varies with spacecraft altitude, being about 10 kilometers near the equator and degrading to as much as 25 kilometers at high latitudes. Black areas indicate where data were not obtained by Magellan. There is a tendency for elevated regions, e.g. the Maxwell Montes (at top center) and Aphrodite Terra (along the equator at right), to show steeper meter-scale slopes than are typical of lower-lying areas. The steeper slopes probably result from disruption of the surface associated with tectonic activity in these regions. Note the large 2300-kilometer (1400-mile) diameter circular feature (Artemis Chasma) in the lower right of the Mercator image. This feature is thought to have been caused by a gigantic plume of heated rock rising from the planet's interior. The data shown here were compiled and analyzed at the Center for Space Research, Massachusetts Institute of Technology. --------------------------------------------------------------------- gtdrp3v2.txt This map of the topography of Venus was obtained by the Magellan radar altimeter during its 24 months of systematic mapping. Color is used to code elevation (see color bar), and simulated shading to emphasize relief. Red corresponds to the highest, blue to the lowest elevations. The upper image shows the portion of the planet between 69 degrees north and 69 degrees south latitude in Mercator projection; beneath it are the two polar regions covering latitudes above 44 degrees in stereographic projection. Height accuracy is better than 50 meters; horizontal ("footprint") resolution of the surface depends on spacecraft altitude, with a resolution of about 10 kilometers (6 miles) near the equator and as much as 25 kilometers (15.5 miles) at higher latitudes. The Magellan altimeter acquired topography data over 98 percent of the planet's surface. Gray areas show the coarser results >from the Pioneer Venus (1978) and Venera 15/16 (1983) radar altimeters, and indicate where data were not obtained by Magellan. The elevated region in the north is Ishtar Terra, dominated by Maxwell Montes (the planet's highest mountains) which rise 11 kilometers (36,000 feet) above the planetary mean elevation. Southwest of Ishtar are the highlands of Beta Regio and Phoebe Regio, which are bisected by a major north-south trending rift zone. The scorpion-shaped feature extending along the equator between 70 and 210 degrees longitude is Aphrodite Terra, a continent-like highland that contains several spectacular volcanoes at its eastern limit: Maat, Ozza and Sapas Montes. The altimetric data shown here were compiled and analyzed at the Center for Space Research, Massachusetts Institute of Technology. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Don't ever take a fence /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | down until you know the |_____|/ |_|/ |_____|/ | reason it was put up.