**GEOLOGIC MAP**

**OF THE**

**KUIPER (H-6)**

**QUADRANGLE**

**OF MERCURY**

By

R.A. De Hon, D.H. Scott, and J.R. Underwood, Jr.

1981

Prepared for the

National Aeronautics and Space Administration

by

U.S. Department of the Interior, U.S. Geological Survey

(Published in hardcopy as USGS Miscellaneous Investigations Series Map
I--1233, as part of the Atlas of Mercury, 1:5,000,000 Geologic Series.
Hardcopy is available for sale from U.S. Geological Survey, Information
Services, Box 25286, Federal Center, Denver, CO 80225)

Please direct questions or comments about the digital version to:

Richard Kozak

U.S. Geological Survey

2255 N. Gemini Drive

Flagstaff, AZ 86001

e-mail: rkozak@flagmail.wr.usgs.gov

**DESCRIPTION OF MAP UNITS**

**PLAINS MATERIALS**

d DARK MATERIAL---Albedo low: occurs as small patches in western part of
quadrangle (8° S., 67°); some overlies bright rays of craters; locally
fills crater floors. *Interpretation:* Basalt flows or pyroclastic
material

ps SMOOTH PLAINS MATERIAL---Smooth, sparsely cratered surface occurs
within craters and topographically low areas between craters. Albedo
intermediate. Representative area: 1° S., 37°. *Interpretation:*
Volcanic rock, clastic blanket generated by secondary impact events, or
both

pc CRATERED PLAINS MATERIAL---Embays or fills most large older craters.
Higher density of craters than smooth plains material; rough planar
surfaces with lobate scarps and broad ridges. In many areas gradational
with smooth plains material. Representative areas: 13° N., 37°; 6° N.,
17°. *Interpretation:* Volcanic rock, clastic blanket by secondary
impact events, or both. Rough surface results from buried and unburied
primary and secondary craters. Crater density indicates age older than
smooth plains

pu PLAINS MATERIAL, UNDIVIDED---Mapped in western part of quadrangle
where high-sun illumination prevents reliable differentiation between
smooth and cratered plains materials (units ps and pc) in craters and
other depressions

pi INTERCRATER PLAINS MATERIAL---Hilly and highly cratered but
intercrater areas are relatively smooth at scale of 5--10 km; most large
craters subdued; many secondaries; embayed by and gradational with
cratered plains (unit pc) in places. Representative area: 8° N., 47°.
*Interpretation:* Oldest crustal material exposed in quadrangle,
volcanic; probably includes ejecta from ancient craters and basins

ptu PLAINS AND TERRA MATERIAL, UNDIVIDED---Mapped only where resolution
of topography is poor because of high-angle solar illumination. Bright
rayed craters common. Albedo ranges from very high around some craters
to intermediate and low. Surface appears generally flat; relief not
determinable on photographs. Representative area: 5° S., 62°.
*Interpretation:* Mostly cratered and intercrater plains materials; may
include some smooth plains and rough terra deposits

**TERRA MATERIALS**

thl HILLY AND LINEATED TERRA MATERIAL---Rugged hills 5--10 km wide and
0.1--1.8 km high, narrow linear troughs, crater rims broken into rings
of hills and depressions. Seen only near 25° S., 22°; maximum
development south of Kuiper quadrangle. *Interpretation:* Structurally
modified terrain antipodal to the Caloris Basin or peripheral to large
impact basin beyond terminator

tr ROUGH TERRA MATERIAL---Very rugged, topographically high and fresh
surface with numerous large- and medium-size young craters; overlaps and
is embayed by smooth plains material. Representative areas: Northeast
and southeast corners of quadrangle. *Interpretation:* Largely ejecta
from young large craters that cannot be mapped separately. Highly
scoured by secondary impacts that formed grooves and chains

**CRATER AND BASIN MATERIALS**

Craters are assigned to five morphologic categories (c1, c2, c3, c4,
c5), which ideally reflect their degradational state and relative age.
Craters less than 30 km across are not mapped. All craters are thought
to have formed by impact

cu CRATER MATERIAL, UNDIVIDED---Materials of craters too poorly resolved
for relative age classification

c5 CRATER MATERIAL---Forms floor, rim, and wall of fresh-appearing
craters. Sharp, rugged, complete rim crest; walls typically terraced;
well defined continuous field of relatively crisp secondary craters;
bright rays or crater materials superposed on all other craters

cp5 CRATER PEAK MATERIAL---Single or multiple rugged peaks near center
of crater

cr5 CRATER RADIAL RIM MATERIAL---Grooved and ridged material extending
outward from raised rim as lineated apron with many secondary craters

sc5 SECONDARY CRATER MATERIAL---Shallow, circular to elongate craters,
commonly overlapping, alined in chains or clusters

c4 CRATER MATERIAL---Similar to c5 craters but less sharp rim crest and
slightly modified wall terraces; very few superposed craters

cp4 CRATER PEAK MATERIAL---Same as cp5 except occurs within c4 craters

cr4 CRATER RADIAL RIM MATERIAL-Same as cr5 except surrounds c4 crater
materials

sc4 SECONDARY CRATER MATERIAL---Same as sc5 except secondary from c4
craters

c3 CRATER MATERIAL---Craters and basins with modified or rounded but
intact rims; field of secondary craters present around larger craters
but less well developed than around c4 and c5 craters. Moderate number
of superposed craters

cpr3 CRATER PEAK OR RING MATERIAL---Central peak or moderately rugged
ring of massifs in center of basins

cr3 CRATER RADIAL RIM MATERIAL---Same as around younger craters but
discontinuous or less well preserved

sc3 SECONDARY CRATER MATERIAL---Secondary craters surrounding larger c3
craters and basins

c2 CRATER MATERIAL---Shallow flat-floored craters and basins with low
rims. No visible secondaries, many superposed craters

cpr2 CRATER PEAK OR RING MATERIAL---Moderately rugged ring of massifs in
center of large craters or basins

cr2 CRATER RADIAL RIM MATERIAL-Discontinuous or narrow apron around
large c2 basins

c1 CRATER MATERIALS---Craters or basins with extremely low or
discontinuous rims

cpr1 CRATER PEAK OR RING MATERIAL---Low, discontinuous, raised rings in
center of largest c1 craters

cpu CRATER PEAK MATERIAL, UNDIVIDED---Central peaks and high-albedo
material in center of cu craters

scu SECONDARY CRATER MATERIAL, UNDIVIDED---Material of alined chains of
craters of unknown age

( cpr3) Symbol in parentheses where concealed by mapped younger deposits

> Contact---Dotted where concealed. West of 50°, poor illumination
> results locally in dashes where approximately located or queries where
> doubtful
>
> Fault---Ball and bar on downthrown side
>
> Ridge in plains material---Symbol on ridge crest
>
> Gentle rounded scarp---Line marks base; barb points downslope. May be
> lava flow front or fault scarp
>
> Irregular scarp---Line marks top; hachures point downslope
>
> Lineament, topographic or tonal
>
> Depression, rimless
>
> Crater rim crest---Hachures point down crater wall
>
> Crater rim crest---Greatly subdued or buried
>
> Ridge crest of multiringed basins
>
> Bright ray material---Plumose streaks or halos on and around some c5
> craters. Visible only at high- sun angle.

**INTRODUCTION**

The Kuiper quadrangle, located in a heavily cratered region of Mercury,
includes the young, 55-km-diameter crater Kuiper (11° S., 31.5°), which
has the highest albedo recorded on the planet (Hapke and others, 1975),
and the small crater Hun Kal (0.6° S., 20.0° ), which is the principal
reference point for mercurian longitude (Davies and Batson, 1975).
Impact craters and basins, their numerous secondary craters, and heavily
to lightly cratered plains are the characteristic landforms of the
region. At least six multiringed basins ranging from 150 km to 440 km in
diameter are present. Inasmuch as multiringed basins occur widely on
that part of Mercury photographed by Mariner 10, as well as on the Moon
and Mars, they offer a potentially valuable basis for comparison between
these planetary bodies.

Basic information about the planetary surface of the Kuiper quadrangle
is provided by three sequences of high-quality photographs designated
Mercury I, II, and III, obtained during the incoming phases of three
encounters of the Mariner 10 spacecraft with Mercury. Mercury I includes
75 whole-frame photographs of the Kuiper quadrangle; Mercury II, 13
whole-frame photographs; and Mercury III, 70 quarter-frame photographs.
The photographs include 19 stereopairs in the southern part of the
quadrangle. For examples of Mariner 10 photography, see Davies and
others (1978). The most distant of the photographs was taken at an
altitude of 89,879 km, the closest at an altitude of 7,546 km.
Resolution, therefore, varies widely but ranges from about l.5 to 2.0 km
over most of the area. A wide range (more than 50°) of both viewing and
solar illumination angles precludes a high degree of mapping
consistency. The easternmost 10° of the quadrangle is beyond the evening
terminator. A low angle of solar illumination and a high viewing angle
make possible discrimination of topographic detail near the terminator.
Higher angles of solar illumination and lower viewing angles make it
increasingly difficult to discern topographic variations to the west.
Many geologic units cannot be specifically identified because of
unfavorable viewing geometry west of approximately 55°. Thus, mapping
reliability decreases westward.

Mapping methods and principles are adapted from those developed for
lunar photogeologic mapping (Wilhelms, 1970, 1972; Wilhelms and
McCauley, 1971). Map units are distinguished on the basis of topography,
texture, and albedo and are ranked in relative age on the basis of
superposition and transection relations, density of superposed craters,
and sharpness of topography. Because of the lack of a widespread, easily
identifiable stratigraphic datum on this part of Mercury, a morphologic
classification of crater and basin materials was the basis for
determining relative ages of many materials. A photomosaic map of the
best available photographs aided greatly in geologic interpretation and
mapping.

**STRATIGRAPHY**

The rock units are subdivided into three major groups: plains materials,
terra materials, and crater and basin materials. The plains and smooth
terra units are considered to be volcanic in part, and thus may have a
different origin from the impact breccias and churned regolith forming
the rough terra and crater deposits.

The oldest rocks exposed in the quadrangle are the intercrater plains
material (unit pi) and the rims of the oldest craters and basins.
Collectively, these rocks form a relatively subdued terrain of moderate
relief. They are similar to some of the rolling and hilly terra and
hilly and pitted materials in the southern lunar highlands, particularly
in the Purbach (Holt, 1974) and Tycho (Pohn, 1972) quadrangles. The
intercrater plains unit is commonly marked by the soft outlines of
numerous overlapping secondary craters producing a subdued hummocky
texture. It is gradational in places with cratered plains material (unit
pc), which forms flat, densely cratered surfaces similar to pre-Imbrian
plains on the Moon (Wilhelms and McCauley, 1971; Scott, 1972) Although
both the cratered and intercrater plains deposits are interpreted to be
volcanic, the latter has been highly degraded by repeated impacts over a
longer period of time. Much of its surface is probably covered by a
relatively thick regolith of reworked impact breccias.

The cratered plains material is relatively flat with broad ridges and
lobate scarps that in places resemble those of some of the lunar maria.
It is difficult to obtain reliable crater counts on this unit because
many secondary craters cannot be distinguished from primary craters.
Cratered plains materials embay craters in classes c1 to c3; they may
represent lava flows extruded after an initial phase of impact flux. The
albedo of the cratered plains is intermediate compared to that of

other mercurian units, but higher than that of the lunar maria, and may
reflect lower iron and titanium content (Hapke and others, 1975).

The youngest rock units consist of rough terra and smooth plains
materials. Rough terra occurs as overlapping and intermixed ejecta
blankets around dusters of large young craters in the eastern part of
the quadrangle. The relief here appears to be higher than elsewhere in
the map area, and the occurrence of dense arrays of fresh secondary
craters produces a coarsely textured, hummocky surface at a scale of
about 10--20 km. The effect of roughness is high-lighted by the low-sun
illumination angle. Ordinarily, rough terra material would be subdivided
and mapped as individual ejecta blankets around and belonging to
particular craters. In this eastern region, however, the closely grouped
craters have about the same age, and it has not been possible to
distinguish the boundaries between their aprons in many places.

Smooth plains material covers the floors of numerous craters in all age
classifications. Its surface is scoured by secondary craters from
classes c4 and c5 craters at many places in the eastern part of the
quadrangle and, within the crater Homer (1° S., 37°), by secondaries
from the class c3 craters Titian (3° S., 42°) and Handel (4° N., 34°).
Thus the smooth plains unit may have a relatively wide age range. Like
the cratered plains, it exhibits lobate scarps and few mare-like ridges,
but these are generally smaller than those of the cratered plains and
more nearly resemble those of the lunar maria. Although crater counts
are more reliable because there are fewer secondaries than in the
cratered plains, resolution is a serious constraint to developing crater
counts on the relatively small tracts of smooth plains. Preliminary
counts made on a few of the more extensive occurrences of smooth plains
show a cumulative crater frequency of about 7.5 x 102/106 km2 for
craters larger than approximately 2.5 km. This frequency is comparable
to that of the lunar maria near the Apollo 11 landing site (Greeley and
Gault, 1970; Neukum and others, 1975; Meyer and Grolier, 1977). Like
that of the cratered plains, the albedo of the smooth plains is
intermediate compared to other units on Mercury (Hapke and others, 1975)
but is relatively high compared to that of the mare basalt on the Moon.

A few patches of very dark material occur in the western part of the
quadrangle where the sun angle is high and albedo contrasts are
enhanced. The largest of these dark patches is apparently superposed on
the bright rays of a c5 crater and is therefore very young.

**CRATERS AND BASINS**

Craters are ubiquitous features of the mercurian surface. For the
purpose of mapping, a five-fold morphologic classification of craters
(fig. 10 in McCauley and others, 1981) is the basis for determining
their relative ages. The youngest craters (c5) have sharp rim crests,
textured ejecta blankets, and a well-defined field of secondary craters.
Under favorable lighting conditions, the youngest craters exhibit bright
rays superposed on all older materials. Older craters have increasingly
degraded rims and lower relief and have lost their secondary crater
fields. The major differences between mercurian and lunar craters are
apparently related to the greater gravitational acceleration and the
higher impact velocities on Mercury. Continuous ejecta deposits are less
extensive, and secondary craters are more sharply defined and clustered
nearer their primary crater. Also on Mercury, accentuated secondary
craters form prominent crater chains radial to large craters.

Craters within the Kuiper quadrangle increase in complexity as they
increase in size from simple bowl-shaped craters to complex craters with
central peaks to multiringed basins. Kuiper (11° S., 31.5°) is a
moderate-size crater with a central peak cluster; Brunelleschi (9° S.,
22.5°) exhibits an incomplete ring of peaks; and Rodin (22° N., 18°) is
a well-developed double-ringed basin. These three craters are mercurian
counterparts in morphology to the lunar craters Copernicus, Compton (or
Antoniadi), and Schrödinger. All craters larger than about 35 km
diameter and basins are filled to some extent with plains materials, and
exposed rims of partly buried craters within the basins indicate that
the fill is about 700 to 1000 m thick (De Hon and Waskom, 1976).

Six basins ranging in age from cl to c3 were formed during the waning
stages of high-impact flux when the surface was virtually saturated with
craters and basins. Later cratering history records a decreasing impact
flux: of craters larger than 50 km diameter, 42 are classed as c3; 19
craters are assigned to c4; and 9 craters are c5. There is also a
decrease in the size of the largest crater or basin formed in each age
class from c2 to c5.

**STRUCTURE**

Structural features are sparse or unresolved in this part of Mercury.
The Kuiper quadrangle apparently has none of the scarps that occur
elsewhere on the planet that have been interpreted as high-angle reverse
faults (Strom and others, 1975). The most prominent structures are the
rings associated with some large craters or basins, faults that transect
crater floors, and lobate scarps and ridges in the plains materials.
Most of the faults and scarps that transect crater floors clearly
delineate crater-filling materials standing at different levels, and in
at least two craters (19° S., 31°; 16° N., 30°), the traces of the
faults on the crater walls indicate that the faults have normal
displacements. A few faults cut intercrater areas and trend generally
northwest or northeast (Scott and others, 1976).

Ridges are broader than many lunar mare ridges and are confined largely
to the cratered plains materials. Antoniadi Dorsum, which is a
well-developed broad ridge north of the Kuiper quadrangle, is less well
developed at its south end and appears in this quadrangle as an
irregular scarp. A number of linear depressions superficially resemble
grabens but are chains of overlapping secondary craters, for example,
Goldstone Vallis (15° S., 32°) and Haystack Vallis (5° N., 46°).

**GEOLOGIC HISTORY**

The interpretable geologic history of the Kuiper quadrangle is primarily
a record of decreasing meteoroid flux during which large craters and
basins formed and plains materials were deposited. A decreasing rate of
crater production is indicated by progressively fewer craters in each
successively younger crater class. Approximately half of the mapped area
contains a high density of craters and multiringed basins formed by the
intense early bombardment. It is doubtful that any primary crustal
material has been preserved without brecciation and redistribution by
repeated impacts. The present crater population represents only the
craters surviving at the end of the stage of highest meteoroid flux. As
the impact flux decreased, cratered plains materials of possible
volcanic origin were deposited in broad, low-lying areas, flooding,
embaying, or partially burying preexisting craters. The youngest
multiringed basins (Renoir, Rodin, and the unnamed basin at 15° S., 15°)
formed near the end of this stage (about c3 time), as did the Caloris
Basin on the opposite side of the planet (McCauley and others, 1981;
Schaber and McCauley, 1980). Craters that formed still later during the
period of low impact rates are well preserved. During this late stage,
smooth plains materials were deposited in basins, craters, and localized
low areas and have low crater density. The youngest craters are sharp
rimmed with bright rays.

The relatively small size of Mercury, its lack of atmosphere, and the
cratered nature of its surface invite comparison with the Moon. The
geologic histories of the two bodies are similar. Both surfaces record a
decreasing impact flux. The cratering history of Mercury was concurrent
with episodes of lava flooding (cratered plains) that may have
obliterated some basins and flooded large areas in a manner similar to
the mare filling on the Moon. Bright-rayed craters, such as Kuiper, mark
the youngest events similar to Copernican craters on the Moon; some dark
patches along the west margin of the quadrangle may represent late
volcanism.

Some differences between the Moon and that part of Mercury observed in
this quadrangle may be more apparent than real. Apparent differences may
be the result of resolution of the imaging system, and small viewing and
illumination angles that do not allow inspection of the surface under
varied conditions. Real differences may be the result of Mercury's size,
gravitational field, proximity to the Sun, internal composition and
structure, or timing of major volcanic episodes relative to the decrease
in impact craters. Surface differences include the preservation of
secondary craters around older craters and basins, and the absence of
recognizable textured and lineated ejecta blankets such as those
surrounding the Imbrium and Orientale Basins on the Moon. Possible
differences in volcanic features include the absence of widespread dark
mare-type deposits, volcanic domes and cones, and sinuous rilles.
Whereas plains and terra divisions may be distinguished on Mercury, the
distinct lunar dichotomy of mare and highlands is not present on that
half of Mercury observed by Mariner 10.

**REFERENCES**

Davies, M. E., and Batson, R. M., 1975, Surface coordinates and
cartography of Mercury: Journal of Geophysical Research, v. 80, no. 17,
p. 2417--2430.

Davies, M. E., Dwornik, S. E., Gault, D. E., and Strom, R. G., 1978,
Atlas of Mercury: National Aeronautics and Space Administration Special
Publication SP-423, 128 p.

De Hon, R. A., and Waskom, J. D., 1976, Geologic structure of the
eastern mare basins: Lunar Science Conference, 7th, Proceedings, p.
2729--2746.

Greeley, Ronald, and Gault, D. E., 1970, Precision size-frequency
distribution of craters for 12 selected areas of the lunar surface: The
Moon, v. 2, no. 1, p. 10--77.

Hapke, Bruce, Danielson, G. E., Jr., Klaasen, Kenneth, and Wilson,
Lionel, 1975, Photometric observations of Mercury from Mariner 10:
Journal of Geophysical Research, v. 80, no. 17, p. 2431--2443.

Holt, H. E., 1974, Geologic map of the Purbach quadrangle of the Moon:
U. S. Geological Survey Miscellaneous Geological Investigations Map
I-822.

McCauley, J. F., Guest, J. E., Schaber, G. G., Trask, N. J., and
Greeley, Ronald, 1981, Stratigraphy of the Caloris Basin, Mercury:
Icarus (in press).

Meyer, J. D., and Grolier, M. J., 1977, Geologic map of the Syrtis Major
quadrangle of Mars: U. S. Geological Survey Miscellaneous Geological
Investigations Map I-995.

Neukum, Gerhard, Konig, Beate, and Arkani-Hamed, Jafar, 1975, A study of
lunar impact crater size-distributions: The Moon, v. 12, no. 2, p.
201--229.

Pohn, H. A., 1972, Geologic map of the Tycho quadrangle of the Moon: U.
S. Geological Survey Miscellaneous Geological Investigations Map I-713.

Schaber, G. G., and McCauley, J. F., 1980, Geologic map of the Tolstoj
quadrangle of Mercury: U. S. Geological Survey Miscellaneous
Investigations Series Map I-1199.

Scott. D. H., 1972, Geologic map of the Maurolycus quadrangle of the
Moon: U. S. Geological Survey Miscellaneous Geological Investigations
Map I-695.

Scott, D. H., De Hon, R. A., and Underwood, J. R., Jr., 1976, The
geology of the Kuiper quadrangle of Mercury (abs.): Conference on
comparisons of Mercury and the Moon, Lunar Science Institute, Houston,
Texas, November 15--17, p. 31.

Strom, R. G., Trask, N. J., and Guest, J. E., 1975, Tectonism and
volcanism on Mercury: Journal of Geophysical Research, v. 80, no. 17, p.
2478--2507.

Wilhelms, D. E., 1970, Summary of lunar stratigraphy---telescopic
observations: U. S. Geological Survey Professional Paper 599-F, p.
1--47.

\_\_\_\_\_1972, Geologic mapping of the second planet: U. S. Geological
Survey Interagency Report: Astrogeology 55, 36 p.

Wilhelms, D. E., and McCauley, J. F., 1971, Geologic map of the near
side of the Moon: U. S. Geological Survey Miscellaneous Geological
Investigations Map I-703.

> **NOTES ON BASE**
>
> This map sheet is one of a series covering that part of the surface of
> Mercury that was illuminated during the Mariner 10 encounters (Davies
> and Batson, 1975). The source of map data was the Mariner 10
> television experiment (Murray, 1975).
>
> ADOPTED FIGURE
>
> The map projections are based on a sphere with a radius of 2439 km.
>
> PROJECTION
>
> The Mercator projection is used for this sheet, with a scale of
> 1:5,000,000 at the equator. Latitudes are based on the assumption that
> the spin axis of Mercury is perpendicular to the plane of the orbit.
> Longitudes are positive westwards in accordance with the usage of the
> International Astronomical Union (IAU, 1971). Meridians are numbered
> so that the reference crater named Hun Kal (lat --0.6°) is centered on
> long 20° (Murray and others, 1974; Davies and Batson, 1975).
>
> CONTROL
>
> Planimetric control is provided by photogrammetric triangulation using
> Mariner 10 pictures (Davies and Batson, 1975). Discrepancies between
> images in the base mosaic and computed control point posi- tions
> appear to be less than 2 km.
>
> MAPPING TECHNIQUES
>
> Mapping techniques are similar to those described by Batson (1973a,
> 1973b). A mosaic was made with pictures that had been digitally
> transformed to the Mercator projection. Shaded relief was copied from
> the mosaics and portrayed with uniform illumination with the sun to
> the west. Many Mariner 10 pictures besides those in the base mosa- ic
> were examined to improve the portrayal. The shading is not
> generalized, and may be interpreted with nearly photographic
> reliability (Inge, 1972; Inge and Bridges, 1976).
>
> Shaded relief analysis and representation were made by Patricia M.
> Bridges.
>
> NOMENCLATURE
>
> All names on this sheet are approved by the International Astronomical
> Union (IAU, 1977).
>
> H-6: Abbreviation for Mercury (Hermes) sheet number 6.
>
> H 5M 0/36 G: Abbreviation for Mercury (Hermes) 1:5,000,000 series;
> center of sheet, lat 0°, long 36°; geologic map, G.
>
> REFERENCES
>
> Batson, R. M., 1973a, Cartographic products from the Mariner 9
> mission: Journal of Geophysical Research, v. 78, no. 20, p.
> 4424--4435.
>
> \_\_\_\_\_\_1973b, Television cartography: U.S. Geological Survey
> open-file report, 35 p.
>
> Davies, M. E., and Batson, R. M., 1975, Surface coordinates and
> cartography of Mercury: Journal of Geophysical Research, v. 80, no.
> 17, p. 2417-- 2430.
>
> Inge, J. L., 1972, Principles of lunar illustration: Aeronautical
> Chart and Information Center Reference Publication RP-72-1, 60 p.
>
> Inge, J. L., and Bridges, P. M., 1976, Applied photointerpretation for
> airbrush cartography: Photogrammetric Engineering and Remote Sensing,
> v. 42, no. 6, p. 749--760.
>
> International Astronomical Union, Commission 16, 1971, Physical study
> of planets and satellites, *in* Proceedings 14th General Assembly
> 1970: International Astronomical Union Transactions, v. 14B, p.
> 105--108.
>
> \_\_\_\_\_\_1977, Physical study of planets and satellites, *in*
> Proceedings 16th General Assembly 1976, International Astronomical
> Union Transactions, v. 16B, p. 325, 331--336, 355--362.
>
> Murray, B. C., 1975, The Mariner 10 pictures of Mercury: An overview:
> Journal of Geophysical Research, v. 80, no. 17, p. 2342--2344.

Murray, B. C., Belton, M. J. S., Danielson, G. E., Davies, M. E., Gault,
D. E., Hapke, Bruce, O'Leary, Brian, Strom, R. G., Soumi, Verner, and
Trask, Newell, 1974, Mercury's surface: Preliminary description and
interpretation from Mariner 10 pictures: Science, v. 185, no. 4146, p.
169--179.