An ancient, relatively bright, circular feature on the surface of a
dark icy moon, such as Ganymede or
Callisto. Palimpsests lack the relief
associated with normal craters and are thought to be impact
craters of which the topographic relief has been eliminated by viscous
relaxation (creep) of the icy surface, probably during the impact itself.
Typical is Ganymede's 340-km-wide Memphis Facula. Such structures hold
important clues to the early thermal history and composition of the
bodies on which they are found. The original meaning, "scraped again,"
refers to a manuscript on a waxen tablet or other writing material from
which an early text was removed and then written over. The value of
palimpsests, in both planetary astronomy and literature, is that, they
preserve a record of the past in the form of something that is partly
hidden from view.
| Memphis Facula, on Ganymede
- In the traditional sense, a palimpsest is a painting that has been
obscured and covered over by a second image. Palimpsests are sometimes
found in the works of Old Masters who, dissatisfied by their own work,
economized by simply painting over their first picture. They have also
been used as a means of stealing a valuable old painting. A painting
over a master work appears to be innocuous, or very bad, and can subsequently
be removed to reveal the original work. [Thanks to Nikoli
A. McCracken for this contribution.]
AND PLANETARY SCIENCE