These observations provided the first evidence for a bifurcated, or double-lobed, object in the solar system. When 1989 PB's orbit was considered secure, the asteroid was numbered 4769 and named Castalia.
Delay-Doppler images involve a non-intuitive, potentially ambiguous geometric projection, but Scott Hudson (Washington State Univ.) has developed techniques for inverting a sequence of such images to estimate the target's shape and rotation state (Hudson, 1993, Remote Sensing Rev. 8, 195). Aspects of this technique and the results of applying his inversion to Castalia (Hudson and Ostro 1994) and other asteroids are on his web page .
Radar-derived shape models of asteroids open the door to a wide
variety of theoretical investigations that previously have
been impossible or have used simplistic models (spheres or
ellipsoids). Optical lightcurves become easier to interpret
and provide new information about the asteroid's rotation and
optical scattering properties; see, for example, the Castalia
section of Hudson's web page.
Dan Scheeres (Iowa State U.) has used the Castalia model to explore the evolution and stability of close orbits about this asteroid. This new area of celestial mechanics has applications to the design of spacecraft rendezvous and landing missions, to studies of retention and redistribution of impact ejecta, and to questions about the origin and lifetimes of asteroidal satellites.
Radar-based models of small asteroids also allow realistic investigations of the effects of collisions in various energy regimes on the object's surface topography, internal structure, and rotation state. Erik Asphaug (NASA Ames) has begun to use the Castalia 3-D model for such calculations.
Shape of Asteroid 4769 Castalia (1989 PB) from Inversion of Radar
Hudson, R. S., and S. J. Ostro. Science 263, 940-943 (1994).
Orbits Close to Asteroid 4769 Castalia.
Scheeres, D. J., S. J. Ostro, R. S. Hudson and R. A. Werner. Icarus 121, 67-87 (1996).
Constraints on Spin State and Hapke Parameters of Asteroid 4769
Castalia Using Lightcurves and a Radar-Derived Shape Model.
R. S. Hudson, S. J. Ostro, and A. W. Harris. Icarus 130, 165-176 (1997).
Deconstructing Asteroid Castalia: Evaluating a Post-Impact State.
Asphaug, E., and D.J. Scheeres. Icarus 139, 383-386 (1999).
Castalia was the name of a nymph pursued by Apollo. Fleeing his
attention, she dived into the earth, whence a spring burst
forth and was given her name. The mythical spring, on Mount
Parnassus at Delphi, was the site of the most important oracle
to ancient Greece. Castalia was sacred to the muses and was
considered a divine source of poetic inspiration. The name
also refers to a genus of aquatic plants of the water-lily
family, distinguished by rounded, floating leaves and large
fragrant flowers of various colors.