Planetary geomorphology methods - Introduction to Planetary Geomorphology - page 33

Table 2.2. (cont.)

Feature a Description

Tessera, tesserae Tile-like, polygonal terrain

Tholus, tholi Small domical mountain or hill

Unda, undae Dune

Vallis, valles Valley

Vastitas, vastitates Extensive plain

Virga, virgae A streak or stripe of color

a Singular, followed by plural form.

which the slope of the terrain covered by that pixel is
determined. For example, a pixel covering ground that is
flat and horizontal, with the Sun directly overhead, would
appear brighter than a pixel of the same type of surface,
but tilted with respect to the horizontal. An overall topo-
graphic map is then generated by integrating the slopes for
the areas covered by each pixel.
Once the topography has been derived, whether from
images or from other techniques, digital elevation mod-
els (DEMs) can be constructed. Topography then can be
shown by contour lines, by colors, or as shaded-relief
maps ( Fig. 2.21 ) to portray the terrain as it might appear
to a viewer from above.
Names for planetary objects and surface features are
determined by the International Astronomical Union
(IAU) through a committee and various subcommittees

(typically, one for each planet). Names on planetary sur-
faces derive from a variety of sources, including historic
telescopic usage on maps of the Moon made centuries
ago. In the Space Age, there has been an attempt to set
speci c themes for naming surface features. For example,
small craters on Mars are named for Earth villages or
towns of less than 100,000 population, while volcanoes
on Io are named for ancient gods dealing with re, such as
Prometheus.
Classes of surface features typically are Latinized, as
given in Table 2.2 . With features named for people
(mostly craters) it is required that the individual be
deceased for at least five years before the name is applied.
The USGS maintains a gazetteer of named features, which
can be accessed at their website http://planetarynames.wr.
usgs.gov/.

Assignments

1. Discuss the fundamental differences between images
produced from the visible part of the electromagnetic
spectrum and images produced from radar systems.

4. Explain the difference between pixel scale and reso-
lution for images.

5. Visit the USGS website for planetary maps and review
how names are assigned to surface features and sum-
marize the process.

2. Discuss the fundamental concept of using impact
crater counts for age-dating planetary surfaces and
explain the difference between equilibrium and pro-
duction distributions. 6. Discuss how an astrobiologist might use a geologic

map of Mars to plan a future landed mission to
search for evidence of past or present life beyond
Earth.

3. Outline the advantages and disadvantages in the use of
laboratory simulations, computer modeling, and ter-
restrial field analog studies to understand geologic
processes on other planets.