PHOTOMOSAICS OF ASTEROID 951 GASPRA

Gaspra2.gif is a set of three photomosaics of asteroid 951 Gaspra, the
first asteroid visited by a spacecraft.  A modified version of this map
is in press.  The northern side includes essentially all the useful imaged
area of Gaspra.  The longitude 270 side includes details from very low 
resolution images, heavily smoothed and processed, and includes artifacts
caused by shape model errors, incomplete mosaic seam removal and poor image
registration.

Gaspra was observed by the Galileo spacecraft on 29 October 1991.
Images are described in:

Veverka, J., et al., 1994.  'Galileo's Encounter with 951 Gaspra: Overview'
   (Icarus, 107:2-17)

and:

Thomas, P.C. et al., 1994.  'The Shape of Gaspra'  (Icarus, 107:23-36)

The latter paper includes a map of radius contours.  I digitized the
contours and interpolated to give a low resolution shape model, then
refined it by fitting it to limbs and terminators in the images.  The
shape model is a matrix of radii at regular increments of latitude and 
longitude.  Positions in the mosaics are controlled by the digital shape 
model.  For this work, the three dimensional convex hull of the shape 
model was projected into the Morphographic Conformal Projection (the 
conventional Stereographic Projection modified for non-spherical worlds).
Longitudes are measured from the crater Charax, just north of the
equator at the more pointed end of Gaspra.

As with all conformal (true shape) projections, the scale in these mosaics
varies, increasing from the centres to the outer edges.  The map projection
is described in:

Stooke, P.J. and Keller, C.P., 1990.  "Map Projections for Non-Spherical
Worlds / the Variable-Radius Map Projections", CARTOGRAPHICA, V. 27, No.
2, pp. 82-100.

This version of the file, with labels intact, is in the public domain.

Philip Stooke,
Department of Geography,
University of Western Ontario,
London, Ontario, Canada N6A 5C2
stooke@sscl.uwo.ca