[108-109] Fig A-1. Eighteen pictures, taken at 42-sec intervals by Mariner 10's two TV cameras, were computer-enhanced and assembled by hand into this photomosaic. The pictures were taken during a 13-min period when Mariner was 200000 km (124,000 mi) from Mercury on March 29 1974, and was rapidly approaching the planet. Latitude and longitude references for the figure are given in (a); (b) identifies some of the geological features. Kuiper was the first marking recognizable on the Mariner pictures taken during the approach to Mercury.

Hun Kal is the reference crater for latitude and longitude on Mercury, almost on the equator at 20 degrees longitude (see Fig. A-3). North is at the top, and the Sun is illuminating the planet from the left.

[110-111] Fig. A-2. This photomosaic of Mercury was constructed of 18 photos taken at 42-sec intervals by Mariner 10 six hours after the spacecraft flew past the planet on March 29, 1974. A large circular basin about 1300 km (800 mi) in diameter straddles the terminator. This is Caloris. Bright-rayed craters are prominent in this view of the planet. The pictures were taken from a distance of 210,000 km (130,000 mi). In (a) latitude and longitude references for the mosaic are provided, and (b) identifies some of the geological features. Again, north is at the top, and the Sun is shining on the planet from the right.

[112] Fig. A-3. A fresh new crater in the center of an older crater basin provides a landmark for the tiny crater named Hun Kal- the Mayan number 20 - which is the basis for positioning the longitudes on Mercury. By definition, the 20° meridian passes through the center of this small crater. Assuming that the spin axis of Mercury is perpendicular to its orbital plane, the latitude of Hun Kal is 0.23°S. This picture, which covers an area of 130 by 170 km ( 90 by 105 mi), was taken from a distance of about 20,700 km (12,860 mi), a half-hour before Mariner made its first close flyby of Mercury, March 1974.

[113] Fig. A-4. From the photomosaic obtained by Mariner, the U.S. Geological Survey is preparing an Atlas of Mercury. A control net of Mercury has been established together with coordinates of over 1000 points from the Mariner 10 photographs. The series of maps of Mercury will be produced at a scale of 1:5,000,000. Topographic and albedo features are portrayed by airbrush techniques similar to an earlier series of maps of the Moon and Mars. The map reproduced here shows the coverage obtained during Mercury I to a scale of 1:25,000,000. The diagonal gap across the map was, of course, filled in by the photographs obtained later at the second encounter.

[114-115] Fig. A-5. The first of the mosaics obtained at the second encounter covers much the same area of Mercury as the incoming mosaic of the first encounter but extends farther into south polar regions. The crater Kuiper is clear in the top part of the picture. North is at the top, and the Sun illuminates Mercury from the left. The black areas represent parts of Mercury that were not covered in this mosaic. The line drawing below relates the mosaic to latitude and longitude on the illuminated disc of the planet at the time of the encounter.

[116-117] Fig. A-6. The second mosaic swings up toward the limb region. Two bright craters in the lower left quadrant of Fig. A-5 are now placed centrally to the right and immediately below the black area of missing coverage on this mosaic.

[118-119] Fig. A-7. This mosaic covers regions to the south at increasing resolution. The two bright-rayed craters are in the upper left-hand quadrant of this picture. The prominent scarp in the middle of the top halt of the picture is named Astrolab after the ship used by d'Urville in Antarctica in 1838-1840. It is located at 45°S latitude and 70° longitude. A system of bright rays radiates from a crater off the right bottom of the mosaic.

[120-121] Fig. A-8. This mosaic covers the southern terminator region. Discovery scarp is at the top center, named after one of Cook's ships on his last voyage to the Pacific during 1776-1780. The south pole of Mercury is located in the large crater with its floor in shadow one-third of the way along the terminator from the bottom of the mosaic.

[122-123] Fig. A-9. Moving northward again, this mosaic is centered about 30°S latitude and 75° longitude. It shows again the twin bright-rayed crater of Figs. A-6 and A-7. The Astrolabe Scarp is one-third the way up the right-hand edge of the mosaic.

[124-125] Fig. A-10. This mosaic extends to the southeast of the twin bright-rayed crater of Fig. A-9. increasing resolution shows a wealth of fine structural detail of the planet's surface.

[126-127] Fig. A-11. Continuing southward, this mosaic shows the South polar region in great detail; the south pole of Mercury is within the shadowed crater one-quarter of the way from the bottom of the right-hand edge of the mosaic. Two mountain tops gleam as tiny spots within the crater. Three large double-ring basins are between 150 and 200 km in diameter. Alongside them, smooth plains contain many ridges and scarps.

[128-129] Fig. A-12. As Mariner flies by the planet it looks at a part of the surface on which the sun is shining from overhead. Craters and mountains cast no visible shadows and surface features are seen as albedo differences, light rings of crater walls streaks rays and light and dark splotches. The center of this mosaic is approximately 90° longitude and 20°S latitude.

[130-131] Fig. A-13. This mosaic is centered about 100° longitude and 40°S latitude. Somewhat closer to the terminator, it provides more shadow detail than the previous mosaic. The area includes some large crater rings with very rugged surrounding terrain and one very prominent double ring that is almost an impact basin.

[132-133] Fig. A-14. An area a little farther south abuts on the previous mosaic. Its center is at 100° longitude and 60°S latitude. The ray systems in the left half of this mosaic can be traced upward into the lower left of Fig. A-13, where there is a very slight overlap of the two mosaics The prominent bright, large crater with its huge central peak is about 100 km in diameter Near to it is the large 200-km-diameter double ring crater, the largest of the three such craters in Fig. A-11 on which the bright, large crater also appears.

[134-135] Fig. A-15. Again the mosaic moves south, this time with a little more overlap with the previous mosaic of Fig. A-14. Part of the large double-ringed crater at the bottom of Fig. A-14 can be seen at the top of this mosaic. The origin of the long rays seen in both Figs. A-13 and A-14 is identified in this mosaic as a fresh young crater with a central peak. It is about 50 km in diameter. The two smaller double-ring basins of Fig. A-11 also appear on this figure.

[136-137] Fig. A-16. Returning to the sun-drenched landscape near to the equator at 80° longitude, this mosaic reveals a crisscrossing area of light streaks from ray craters. This whole area was foreshortened near the limb of the planet as seen in the two mosaics of Mercury I encounter.

[138-139] Fig. A-17. Another area close to the limb regions of the incoming and outgoing mosaics of the first encounter is shown here in a region centered just north of the equator at longitude 110°. There is slight overlap with Fig. A-16. The small irregular dark splotch at the top left of Fig. A-16 (close to a bright crater) is near to the bottom right corner of this mosaic.

[140-141] Fig. A-18. This mosaic covers an area to the east of A-17 the bright ray crater bottom right of A-17 is top left on this mosaic. The mosaic is centered about 125° longitude and 15°S latitude.

[142-143] Fig. A-19. Moving its cameras southward and toward the terminator, Mariner 10 took this series for a mosaic centered about 135° longitude and 30°S latitude. The mosaic is dominated by a bright-ringed large crater almost at its center. Just above it is a large basin that shows a ruined inner ring.

[144-145] Fig. A-20. South still more and toward the evening terminator, this mosaic shows enormous detail again under low Sun angles. A bright-rayed crater dominates the lower part of the picture. This is the bright-rayed crater of Fig. A-15. North of it and to the west are some unusually long narrow valleys and several prominent scarps. Another young, bright-rayed crater dominates the northern part of this mosaic. There are many large areas of smooth plains material, including a large filled basin marred by subsequent major impacts.

[146-147] Fig. A-21 Centered about 90° longitude and 15°S latitude, the mosaic shows some of the areas covered earlier but from a different viewpoint. The picture is dominated by albedo markings under a high illumination with virtually no shadow detail.

[148-149] Fig. A-22. This mosaic provides details toward the south pole along longitude 120°. Again it is dominated by albedo markings and light rays. The spacecraft was leaving Mercury so that resolution is decreasing.

[150-151] Fig. A-23. The south polar regions are seen here from the opposite side of the planet from Fig. A-11. This mosaic is centered at 160° longitude and 45°S latitude. Close to the right edge of the mosaic is the large crater with its bright rim which is centered in Fig. A-19. Note the bright crater with a central peak and dark halo in the center of the left of the picture. This crater appears at the bottom of the next mosaic but on a smaller scale.

[152-153] Fig. A-24. The final mosaic of the second encounter sweeps northward to include the Caloris Basin, seen from a somewhat different viewpoint compared with the first encounter.

[154-155] Fig A-25. The Caloris Basin as imaged at the three encounters is shown in this series of photographs in the computer-enhanced mosaic from Mercury I (a) is outlined the area viewed at Mercury II (b). The small white boxes identify the locations of the high-resolution frames (c) and (d) obtained at Mercury III. Alongside (d) is shown a high-resolution picture of the same crater-tentatively termed the "Teddy Bear"-taken at Mercury I (e).

[156] Fig A-26. This unusual view of Mercury was prepared from hand assembly of individual pictures, computer-enhanced and projected for a viewpoint close to the south pole. The crater containing the south pole of Mercury is the large one in shadow on the terminator at the bottom of the mosaic. This view links many of the former mosaics.

[157-159] Fig. A-27. Shown on the following two pages are comparative views of the incoming and outgoing mosaics of Mercury I and a wide-angle polar view obtained during Mercury II presenting a view similar to Fig. A-26. Several features are identified on each mosaic and shown in high-resolution images alongside.

[160-161] Fig. A-28. This shaded relief map of the Beethoven quadrangle of Mercury is one of a series of maps of the planet prepared by the United States Geological Survey for NASA. This series of topographic map sheets covers that part of the surface of Mercury that was illuminated during the Mariner 10 encounters. The maps are based on the images returned by the Mariner 10 television experiment.

[162-163] Fig. A-29. Close inspection of the many individual frames used to make the mosaics of the earlier figures provides a wealth of new information about the innermost planet. The presence of other large basins was confirmed in (a) is shown a flooded 240-km (150 mi) diameter basin, its walls indicated by arrow heads, as revealed at Mercury I Another flooded basin (b) photographed at Mercury II is 350 km (220 mi) in diameter and appears to be flooded with plains material and then subsequently cratered by some large impacts. Not only did the filling material partially inundate small craters which had formed along the rim of the basin at the lower left but also overflowed the rim and spilled onto the surrounding terrain at the top right.

[164] Fig. A-30. Victoria Scarp is one of many large lobate scarps on Mercury. It was named after the first ship to sail around the world under the command of Magellan and del Cano in 1519-1522. It is located at 48°5 latitude and 35° longitude. The picture of the scarp obtained at Mercury I is shown in (a): outlined is the area imaged at Mercury III (b) shown alongside. A computer-processed version of the Mercury I image projected to appear as if looking directly down on it is shown in (c). This orthographic projection is used for map making but, of course, lacks fine details in the highly foreshortened regions of the original projection.

[165] Fig. A-31 Discovery Scarp, at latitude 52°S and longitude 35°, was photographed at the first, second, and third encounters. A Mercury I picture (a) shows the scarp transecting craters on the right side of the picture. A smaller scarp runs through the floor of a large crater at the top and into surrounding terrain. This picture also shows two long, narrow valleys consisting of many small craters. Mercury II (b) shows the southern section of the scarp from a somewhat different viewing angle. The two transected craters are not included in this image. Mercury III (c) provides high-resolution detail of the northern section of the scarp and again shows the transected craters. The viewing angle is very similar to that of Mercury I. Note that in the larger crater there is a graben-type valley to the right of the scarp, but no such feature in the smaller of the transected craters.

[166-167] Fig. A-32. The jumbled terrain antipodal to the Caloris Basin was also covered in detail by Mariner. A photomosaic from Mercury I (a) shows the peculiar nature of this area of hills and ridges cutting across craters and intercrater areas. The rims of flat-floored craters are partially disrupted and hills are dissected. A close view of part of this terrain is shown in (b, and an even closer view in (c). A high-resolution frame within the area obtained by Mercury III is shown in (d). Since this terrain is antipodal to the Caloris Basin, it has been speculated that it may have been caused by a focussing of seismic forces originating from the Caloris impact.

[170-171] Fig. A-35. Centered 75°S latitude and 70° longitude, this area includes several scarps. Note the terraces on the inside walls of many of the craters and the difference in level of the crater floors on either side of scarps that pass through them.

[172-173] Fig. A-36. Centered at 64°S latitude and 64° longitude, this area shows another prominent but as yet unnamed scarp. Note how it passes through the floor of the large terraced crater at the bottom left, showing that the crater was formed before the scarp.

[174-175] Fig. A-37. Centered at 54°S latitude and 49° longitude, this stereo pair shows the southern end of Discovery Scarp. The pictures have been printed with north toward the left to provide the stereo effect. Note the crater chains radiating from the prominent fresh crater on the large ruined ring in the bottom left quadrant. Also note the fluted walls of the crater shown partly at the extreme top left of the picture.