VENUS SURFACE GRAVITY MAPS
                      from Magellan Mapping Cycles 4 and 5
                                January 30, 1994

This GIF image was made from data supplied by the Magellan Gravity Team at the
Jet Propulsion Laboratory, Principal Investigator William L.  Sjogren. The
original data, ID MGN-V-RSS-5-GRAVDR-L2-V1.0, may be obtained from the
Geosciences Node of the NASA Planetary Data System.

              FREE-AIR VERTICAL SURFACE GRAVITY MAP (DMGJV40E.B01)

This image of the free-air gravity field was generated at a reference radius of
6051.0 km from a fortieth degree and order spherical harmonic model (MGN40E)
with a grid spacing of one degree.  The model was determined using Doppler radio
tracking data from the Magellan spacecraft on cycles 4 and 5 (Sept. 1992 to Nov
1993).  There was also an a priori constraint on the coefficient power spectra
of 1.2x10^-5/(n^2), where n is the spherical-harmonic degree of the coefficient.
The largest positive gravity anomalies are associated with Beta Regio (200
milligals, latitude 25N, longitude 281E) and Atla Regio (203 milligals, 2N,
199E), which are topographically high regions.  The largest negative anomalies
are all in the lowlands, ranging from -40 to -80 milligals.  The amplitudes of
the anomalies are similar to those of the Earth, but unlike those of the Moon
and Mars which are much larger.  However, there is almost perfect correlation of
topography with gravity (highs with highs and lows with lows) which is not the
case for the Earth, where some gravity highs occur in the oceans and some
gravity lows occur over continents.

                FREE-AIR GRAVITY UNCERTAINTY MAP (DMGJV40E.B01)

The best determination or smallest uncertainty in the gravity field solution is
shown by the small values stretching across the equatorial zone.  This is the
result of excellent data from Magellan cycle 4 coverage during the period from
September 1992 to May 1993.  Another excellent block of data was acquired during
cycle 5 after a successful aerobraking which placed the spacecraft in a near
circular orbit and provided data for the polar regions.  The larger
uncertainties between 90E and 215E are due to the fact that there is presently
no coverage from cycle 5 in this area.  It is anticipated that this will be
greatly reduced by September 1994.  These results were produced from the formal
covariance matrix of the 1677 parameters in the 40th degree and order model and
probably are optimistic by a factor of 3 to 5.

                        SURFACE GEOID MAP (DMOJV40E.B01)

The surface geoid shows height variations in an equipotential surface referenced
to the mean planetary radius. It is determined from the same set of spherical
harmonic coefficients estimated for the gravity field.  The comments made about
the free-air vertical gravity map are applicable to this geoid image as well.
The peak amplitudes again are over Beta Regio (113.7 meters, 25N, 281E) and Atla
Regio (141.4 meters, 2N, 199E).  The surface is smoother than the gravity map
because the gravity field is less sensitive to shorter wavelengths.
Nevertheless, all the larger features appear in essentially the same areas as in
the free-air gravity image.

                   BOUGUER SURFACE GRAVITY MAP (DMBJV40E.B01)

A Bouguer map is produced by subtracting from the observed free-air vertical
gravity a theoretical vertical gravity based on the topography assuming a
density similar to earth's crustal rocks, assumed here to be 2900 kg/m^3.  If
the observed gravity was produced from rigid surface topography only, the
difference would be zero.  This certainly is not the case for there are very
large differences, especially in the Aphrodite region 70E to 150E near the
equator and the Ishtar Terra region at 65N latitude.  These differences indicate
that the topography is less compensated in some manner.

Reference GM                 = 324858.5578 km^3/sec^2
Reference Gravity Radius     = 6051.0 km
Reference Density            = 2900 kg/m^3
Reference topographic radius = 6051.839 km