MAGELLAN PROJECT OFFICE

MIT ID: GREDRP.1;2
JPL ID: P-40348
Date:   6/15/92

These images show  the  distribution  of  radar  reflection  coefficient
(reflecting  efficiency)  of the Venus surface when viewed from directly
overhead by the Magellan altimeter. The  lightest  shades  locate  areas
having  the  highest values of normal-incidence reflectivity (as high as
70 percent in  places),  while  darker  shades  indicate  areas  of  low
reflection  efficiency.  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  had  not  yet been obtained by Magellan after the
first eight months of operation.

There is a tendency for elevated regions, e.g. the Maxwell Montes  (left
of the data gap at top center) and Aphrodite Terra (along the equator at
right), to show higher  values  of  reflectivity  than  are  typical  of
lower-lying  areas.  The  highest  values  (greater than 30 percent) are
puzzling to understand. On a cooler planet such as Earth or Mars,  water
or  ice  might  explain  the observations, but at the 470-degree-Celsius
temperature of the Venus surface, neither can be present. Some  theories
require  the presence of minerals such as iron pyrites; others suggest a
material, as yet unidentified, that has extremely low  electrical  loss.
The  data shown here were analyzed and projected at the Center for Space
Research, Massachusetts Institute of Technology.