Article,
Evolution of lineaments on Europa: Clues from Galileo multispectral imaging observations
Icarus, 135 (1): 107--126 (1998)
Abstract
Four distinct classes of lineaments can be described on the basis
of Galileo's improved spectral and spatial coverage of Europa: (1)
incipient cracks are narrow (<1.6 km wide) and are generally colorless
fractures which tend to crosscut other lineament types, (2) ridges
have raised relief, tend to be wider (3-6 km) than the cracks, and
are distinct in color from the icy plains they transect, (3) triple
bands have dim medial stripes similar in color and width to the ridges
and broad (8-12 km wide) diffuse low-albedo margins tainted by a
red-brown non-ice contaminant, and (4) ancient bands are generally
similar in width to ridges and triple bands and have colors intermediate
between those of triple bands and the undisturbed icy plains. They
are only slightly darker than the plains at visible wavelengths-hence,
they were largely undetected by Voyager-but are distinctly brighter
than the plains in the infrared, precluding the possibility that
they have simply faded from their formerly darker appearance. The
morphologies, spectral properties, and orientations of the lineaments
vary systematically with age, suggesting that these four classes
represent different stages of development in an evolutionary sequence.
Lineament formation appears to be the dominant resurfacing mechanism
on Europa, and every landscape that has escaped erasure by heating
from below is imprinted with generation after generation of intersecting
ridges at various scales and orientations, Relatively recent fractures
expose coarse-grained, clean ice in the shallow subsurface, possibly
accounting for the distinctive color of the satellite in comparison
to the other icy moons of Jupiter, The process of lineament formation
may be continuing today; the bright band Agenor Linea is among the
leading candidates for current activity. (C) 1998 Academic Press.
