Part II - The Researcher's Description

1		MERCURY - Caloris Basin This image shows the eastern half of a large (1300-km diameter) circular feature on the planet Mercury known as the Caloris Basin. The basin is marked by a large concentric ring stretching from the top to the bottom of the image on the left side and by ridges and fractures on its floor. It was probably formed by the impact of a large meteoroid on the planet's surface, just as large basins on the Earth's Moon were formed. Also like the Moon, Mercury is covered with smaller impact craters. Mercury is similar to the Moon in other ways. Both have practically no atmosphere, so their surfaces are not shaped by the presence of wind and water. Features like sand dunes, river valleys, or beaches do not appear on these bodies. As the planet closest to the Sun, Mercury has a surface temperature that can reach 427 degrees Centigrade. The name Caloris comes from the Latin word for heat.
2		VENUS - Sapas Mons In the center of this computer-generated perspective view is Sapas Mons, a large volcano. Sapas Mons is 400 km across and 1.5 km high. In the image, you can see lava flows hundreds of kilometers long that come from the volcano. On the top of Sapas Mons is a large summit crater. This scene has been vertically exaggerated 10 times, so the volcano appears steeper than it really is. The color in the image is an approximation of what you would see if you were standing near Sapas Mons (which, because of the high temperatures and pressures on Venus you couldn't, but we'll use our imagination!). Because of the thick cloud cover of Venus, the Sun's light produces this orange hue. However, if we brought a rock back from Venus, it would probably look kind of gray.
3		VENUS - Global View This global view of the planet Venus is a mosaic of images from the Magellan mission. The Magellan radar mission was able to map almost all of the surface of Venus, because radar instruments can see through dense clouds like those that enshroud the planet. The atmosphere of Venus is mostly carbon dioxide. The temperature at the surface is hot enough to melt lead. The bright band that runs across the planet is a highland area of mountains and canyons. Many of the dark areas represent lava flows. Craters are present, but not in the same abundance as on the Moon and Mercury.
4		VENUS - Venera View of the Surface This view of the surface of Venus came from the Russian Venera 13 lander. Venera 13 soft-landed on Venus in March 1982. It operated for about 2 hours before its instruments succumbed to the planet's tremendous heat. The image shows flat rocks and dark soil. The banded arm extending from the spacecraft on the far right was for matching color accurately.
5		EARTH - Earth from Apollo 17 Apollo 17 astronauts captured this unforgettable view of the Earth as they looked back toward home on their journey to the Moon. White clouds swirl in the atmosphere, and blue oceans cover much of the planet. The continent of Africa appears brown. On the northeast corner of the continent, and separated from it by the Red Sea, is the Saudi Arabian peninsula. East of Africa is the island of Madagascar. In the south, the white ice continent of Antarctica can be seen through the clouds.
6		EARTH - Grand Canyon, Arizona The Grand Canyon in Arizona can be seen in this Space Shuttle photo as a network of sinous valleys running mostly along the bottom of the image. Carved by the Colorado River, the entire Canyon is 349 km long, and from 8 to 25 km wide--a spectacular example of how water shapes the face of our planet. The layers of rock on its walls get older and older the deeper down the canyon you go. At its deepest points (about 1800 m down) the rocks date to what is known as Pre-Cambrian time, more than 570 million years ago.
7		EARTH - Space Shuttle View of Hawaii The Big Island, Hawaii, is the largest and youngest of eight major islands that make up the 50th state of the United States. The island is the top of a huge mountain made up of five volcanoes whose summits rise above sea level. In the center of the photo, with dark strands of cooled lava flows extending on all sides, is Mauna Loa, an active volcano in the Hawaii Volcanoes National Park. Note that some of the lava flows extend all the way to the ocean. The feature in different shades of brown to the north of Mauna Loa is Mauna Kea, inactive for thousands of years. It is Hawaii's highest peak and the site of several astronomical observatories.
8		MOON - Moon from Apollo 17 This Apollo photograph shows the east side of the Moon. Because the same face of the Moon always points toward Earth, this is a view that we cannot see with ground-based telescopes. Notice the dark circular regions. These are large basins caused by the impact of giant meteoroids billions of years ago. Millions of years after the basins were formed, dark lavas flooded up through cracks in the crust, filling the low-lying basins and producing the appearance we see today. The lighter-colored regions covering much of the rest of the surface are the ancient highlands. Note that this old terrain has many more craters that the younger dark basin plains.
9		MOON - Hadley Rille In July 1971, Apollo 15 astronauts landed near Hadley Rille on the east edge of Mare Imbrium near the lunar Apennine Mountains. The rille is a long, sinuous valley that may be like a lava tube on Earth. These tubes form at the edge of lava flows as they cool and solidify, and molten lava drains away. The rille is about 1.5 km wide, and 300 meters deep. The astronauts used a lunar rover to travel to the rim of the rille to explore. The dark smooth areas are lava rocks called basalts. The rugged mountains are the rim of the Imbrium Basin, and they rise about 5 km high in this area.
10		MARS - Candor Chasma Candor Chasma is a deep canyon along the central part of the great valley called Valles Marineris. It was probably formed originally by faulting, and enlarged by the downslope movement of rock and soil, called mass wasting. Wind, water, and volcanism may have contributed to its present appearance.
11		MARS - Global View - Valles Marineris Hemisphere One hundred and two Viking Orbiter images were combined to produce this global mosaic of Mars. Stretching across the center of the image is Valles Marineris (Mariner Valley), a huge canyon over 300 km long, and up to 8 km deep. The three brown circles on the left are very large volcanoes about 300 km across, larger than any volcano on Earth. You can not see as many craters on Mars as you can see on the Moon or Mercury. Here the action of wind and water has obliterated many old features.
12		MARS - Olympus Mons Oympus Mons, with a diameter of 624 km, is the largest volcano on Mars. It is a shield volcano like those found in Hawaii, only much larger. It is 25 km high, and at its base is a scarp that rises several kilometers above the surrounding terrain. At its summit is a crater, or caldera, made up of smaller overlapping collapse craters, each formed during a different volcanic episode.
13		MARS - Viking Lander 1 View of the Surface This scene from the surface of Mars shows a world very different from the Moon or Mercury, a world influenced by the presence of an atmosphere. The reddish sky comes from dust blown by Martian winds. The small dunes are formed from windblown sand. For scale, the rock in the center is about 2 meters across, and 1 meter high.
14		JUPITER - Ring Voyager I first discovered the existence of a ring around Jupiter in 1979. This image was collected as the Voyager 2 spacecraft looked at Jupiter's limb (edge) from behind the dark side of the planet. The three layers in Jupiter's limb are not real, but are an artifact of image processing. The ring extends beyond the field of view of this image, so its outer edge is not visible. The slender ring is made up of very fine dust particles. It may have formed from the breakup of a small moon or from material that never came together to form a moon.
15		JUPITER'S MOONS - The Galilean Satellites Four large moons of Jupiter are depicted here. (Clockwise from upper left: Io, Europa, Callisto, Ganymede.) These moons are called the Galilean satellites because they were discovered by Galileo using his telescope in 1610. Io has no visible impact craters, indicating a young surface of relatively new volcanic flows that have covered the old cratered terrain. Europa displays puzzling linear markings with no topographic relief. Europa may have a thin crust made of ice with a 50-km deep ocean underneath. Callisto's surface is covered with old degraded craters and basin rings, that indicate that this moon's face is very old. Ganymede, the largest moon in the Solar System, exhibits two different types of terrain: an old cratered landscape, and a younger region of parallel grooves that indicate the stress of tension from tectonic activity.
16		JUPITER'S MOON - Io Io is a world of active volcanism. The features you see with circular haloes are very large volcanoes. Hundreds of other volcanic structures dot the surface. The Voyager 1 and 2 spacecraft both observed volcanoes on Io as they were erupting. This was the first time volcanic activity had been observed on a planetary body other than our own.
17		JUPITER - Shoemaker-Levy 9 Comet Impact In July 1994, fragments of the comet Shoemaker-Levy 9 impacted the planet Jupiter, giving scientists their first chance to observe such a collision as it happened. This image from the Hubble Space Telescope shows the site of two fragment impacts. Jupiter is known as a gas giant, and is made up mostly of hydrogen and helium in gas and liquid form. It is thought to have a small core of molten rock. When we observe Jupiter, we are not looking at a solid surface. What we see is a banded atmosphere with swirling clouds and huge storms.
18		SATURN The elaborate ring system of Saturn surrounds the planet in this Voyager 2 true color view. Three moons, (from top to bottom) Tethys, Dione, and Rhea, are visible. Tethys casts a shadow on the banded planet. Rhea is the faint dot in the bottom left corner of the image. Saturn is a gas giant, and is made up mostly of hydrogen and helium in gas and liquid form. It is thought to have a small core of molten rock. When we observe Saturn, we are not looking at a solid surface. What we see is an atmosphere that is banded but lacks the elaborate atmospheric patterns visible on Jupiter, its larger neighbor.
19		SATURN - Ring Structure The complexity and intricacy of Saturn's rings surprised observers when the rings were first viewed in detail by the Voyager spacecraft. They are composed of icy particles that vary greatly in size, ranging from as small as dust particles to as large as a house. The ring system is 67,000 km wide. Broad large rings are composed of narrower rings, and gaps between rings vary in size.
20		NEPTUNE This Voyager 2 scene of Neptune, another of the planets called gas giants, was collected when the spacecraft was 14.8 million kilometers from the planet. Bright clouds can be seen around the Great Dark Spot (GDS) in the lower right, and subtle banding is evident in the atmosphere. The GDS, a huge atmospheric storm, is as large as the Earth.
21		NEPTUNE'S MOON - Triton Triton is Neptune's largest moon (2700 km in diameter). It has active geysers that erupt nitrogen and dark dust high into the very thin atmosphere. In this image, the brighter area at the bottom is a frozen polar cap composed of methane and nitrogen. Triton holds the record for the coldest surface temperature observed in the Solar System, about -235 degrees Centigrade. Its orbit is retrograde suggesting it did not originate in the Neptune system but journeyed from elsewhere and was captured by Neptune's gravity.
22		URANUS The true color image of the gas giant Uranus (left) shows a nearly featureless atmosphere with only extremely subtle variations visible. Image processing using false color and contrast enhancement (right) brings out these subtle features to show a dark polar region and concentric bands. One theory is that haze concentrating over the pole forms these bands.
23		PLUTO and CHARON A spacecraft has never visited Pluto, and this planet is so far away from Earth that even the Hubble Space Telescope can't show us much detail. Pluto and its moon Charon are often called a double planet because of their relative sizes and the short distance separating them. In this Hubble Space Telescope image, the two discs can be distinguished separately, enabling scientists to get a more accurate measure of their diameters (Pluto: 2320 km; Charon: 1270 km). The image was acquired from a distance of 4.4 billion km. The different color of the two bodies indicates that they have a different surface composition.

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