Set of 10: 1991 Space Exploration Series

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29USA MERCURY MARINER 10 CA DEN OCT 1991 91109 PAS JUPITER PIONEER 11 29USA DEN PASA OCT 1993 91109 ADENA 91109 VENUS MARINER 2 29USA ASADENA9USA OCT EARTH LANDSAT 1991 91109 CA MARS VIKINGORBITER PASADENS OCT へ29USA 1. 1991 91109 CA ENA PASA OCT 199 1109 MOON LUNAR ORBITER 29USA PLUTO NOT YET EXPLORED 29 USA ADENA SATURN VOAGER2 ADENA9USA 1991 91109 CEL URANUS VOYAGER 2 29USA DENA 1OCT 1991 91109 CA NA NEPTUNE VOYAGER 2 29USA L109 CA

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MERCURY WITH MARINER 10 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Launched in November 1973, Mariner 10 approached Mercury on three separate occasions through March 1975, coming as close as 200 miles to the planet's surface and sending back data and photographs that show a world with amazing contrasts. Mercury has an ancient surface resembling the Earth's Moon, heavily scarred by meteor- ite impacts. One such crater is more than 500 miles across. The planet is also characterized by a feature unique to the Solar System — long, curved scarps (cliffs) that appear to be the result of compression on the planet's crust as it cooled. But on Mercury, cool is a relative term: the planet's surface temperature on the side facing the sun is 950°F. In contrast, Mercury's tenuous atmosphere of argon, neon and helium — a trillionth the density of Earth's atmosphere – retains virtually no heat on the planet's night side, with a resulting temperature of -350°F. Mariner 10 also revealed that Mercury has a weak mag- netic field, and that the small planet's core is likely comprised of iron. No. 91-78 ©1991 The Maximum Card Collection A division of Unicover Corporation . Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA JUPITER WITH PIONEER 11 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Braving the asteroid belt that separates Mars from Jupiter, Pioneer 11 approached the gigantic fifth planet in De- cember 1974. Powered by a nuclear reactor because the planet's distance from the sun made solar cells unwork- able, the valiant craft confirmed that Jupiter is mainly composed of liquid hydrogen, the element that supports nuclear fusion on the sun. And though its mass is insuffi- cient to cause the runaway fusion that would class it as a star, Jupiter still generates two-and-a-half times more energy than it receives from the sun. The giant planet further resembles a star in that it is surrounded by satellites mimicking the Solar System in miniature. Ganymede, for example, is larger than either Pluto or Mercury. Much speculation has taken place about Jupiter's Great Red Spot. The planet's only permanent feature, it has been observed for hundreds of years. Pioneer 11 revealed it to be a massive storm. Despite the data gathered by Pioneer, scientists still marvel at the mysteries surrounding this unique would-be star. No. 91-79 ©1991 The Maximum Card Collection A division of Unicover Corporation . Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA VENUS WITH MARINER 2 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Launched August 27,1962, Mariner 2 was America's first successful planetary spacecraft - a notable milestone in the onrushing “Space Race." In December of that year, Mariner 2 flew past Venus, making observations of a planet that has fascinated mankind since the dawn of history. Named for the Roman goddess of beauty because of its brightness in the early evening sky, Venus is on its surface anything but beautiful. Beneath bright cloud cover, temperatures rise to 800°F — hot enough to melt lead both day and night. And despite its deceptively brilliant appearance, Mariner 2 confirmed that there is never a sunny day on Venus, finding no breaks in the omnipresent clouds. A subsequent Mariner flight discov- ered that the Venusian atmosphere is composed of at least 80% carbon dioxide, giving credence to the earlier-held theory that Venus' intense heat is the result of the Green- house Effect. Also found in a high concentration in the exceedingly dense atmosphere of Venus is sulphuric acid, a major component of acid rain on Earth. No. 91-80 © 1991 The Maximum Card Collection A division of Unicover Corporation • Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA EARTH WITH LANDSAT First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Also known as Earth Resources Technology Satellites, Landsat spacecraft began mapping the planet in 1972. Their primary mission was charting Earth's natural re- sources. A further objective was to detect variations in pollution levels and other ecological changes. Landsat was a brilliant success, providing mapmakers with far more accurate reference than could be obtained even by high-flying airplanes. Infrared photos taken by Landsat revealed a number of interesting phenomena, among which is that cities form massive heat sinks, absorbing solar energy by day and releasing it at night. Another fascinating Landsat photo reveals Mississippi River pollu- tion entering the Gulf of Mexico, looking like a plume of smoke in the clear blue sky. Other Landsat photos show the only man-made structure visible from outer space — the 1,500-mile-long Great Wall of China. In addition to mapping natural resources, Landsat photos have helped Pacific fishermen locate prime fisheries, warned sailors of icebergs, and even helped track oil spills. No. 91-81 ©1991 The Maximum Card Collection A division of Unicover Corporation Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA MARS WITH VIKING ORBITER First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California So similar to Earth, yet so different, Mars has all the ingredients necessary for life as we know it. So said the Viking spacecraft, which explored the Red Planet begin- ning in 1976. The Martian atmosphere contains oxygen, nitrogen, carbon dioxide and even water vapor, though the planet is drier than Earth's driest desert. Still, evidence gathered by Viking shows that at one time water flowed on Mars. There are abundant channels apparently carved by running water — and scientists analyzing Viking data theorize there was once enough water there to cover the entire planet 33 feet deep. Other Viking data suggests that Mars was once much warmer and its atmosphere substan- tially thicker than at present. Today, the Martian atmo- sphere is but 1/100th as thick as Earth's and temperatures are bitterly cold, with daytime highs only approaching -20°F. Despite the wealth of information gathered by Viking, a number of questions remain. What happened to all the Martian water? And is there life on Mars? No. 91-82 ©1991 The Maximum Card Collection A division of Unicover Corporation . Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA MOON WITH LUNAR ORBITER First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California From 1966 to 1967 — coming as close as 29 miles to the lunar surface — NASA's Lunar Orbiters photographed 99% of the Moon, including both polar regions and the mysterious dark side. It was an amazing feat considering that three of the five Orbiters experienced equipment failures. From the high-resolution photographs, maps 100 times more accurate than previously possible were cre- ated, and several primary landing sites for upcoming Apollo missions were chosen. NASA didn't take any chances — it was vital to avoid locations where craters, rocks and holes filled with dust could be hazardous to the lunar module. Thus, when the Apollo 11 astronauts made their historic trip, their landing site was the basaltic surface of the Sea of Tranquillity, an area shown to be virtually crater-free by the Lunar Orbiters. As a result, when astronaut Neil Armstrong made his “giant leap for mankind," he was following in the figurative footsteps of the intrepid Lunar Orbiters, which had blazed a safe trail for him and all subsequent Apollo astronauts. No. 91-83 ©1991 The Maximum Card Collection A division of Unicover Corporation Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA PLUTO First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Astronomer Percival Lowell, studying the then-most- distant planet Neptune, couldn't explain its erratic orbit. Neptune appeared to slow down, then speed up again. The phenomenon mystified the American scientist. Then he had an astounding thought. Could there be another, as- yet-undiscovered planet influencing Neptune's orbit? Unfortunately, Lowell didn't live to see his prediction about “Planet X” realized. But in 1930, Clyde Tombaugh, a young assistant astronomer at the Lowell Observatory in Arizona, made an amazing discovery. Comparing two pictures of the same star field taken days apart, he noticed one “star” had moved – exactly where Lowell had predicted 16 years earlier. “Planet X” had been unmasked and suddenly text books at grade schools around the world were out of date. Since its discovery, most have assumed that the Solar System ends at the ninth planet. But recently, astronomers have found eccentricities in the orbits of both Neptune and Pluto. Could a tenth planet lurk beyond? No. 91-84 ©1991 The Maximum Card Collection A division of Unicover Corporation • Cheyenne, WY 82008-0007 Photograph courtesy of NASA SATURN WITH VOYAGER 2 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California Most conspicuous of the sun's planets, Saturn is also among the most enigmatic. First reached by Voyager 2 in August 1981, Saturn is beset by gigantic thunderstorms. Voyager 2 also revealed that, like Jupiter, Saturn radiates more heat than it receives from the sun. But its amazing rings are the key reason Saturn has fascinated mankind for centuries. Once thought to be unique in the Solar System, Saturn's rings can be clearly seen from Earth using a low- powered telescope. Further explorations of Voyager 2 revealed that Jupiter and Uranus have similar rings. But it is the well-defined rings of Saturn about which scientists since Galileo have speculated. Voyager 2 confirmed what many had thought — that Saturn's rings are for the most part composed of water ice. The same is true of Saturn's many moons, except for Titan, the largest, which is remarkably Earth-like. Titan's atmospheric nitrogen level is similar to Earth's, as is its water content. However, the Saturnian satellite is bitterly cold — with a surface temperature of -288°F. No. 91-85 ©1991 The Maximum Card Collection о A division of Unicover Corporation • Cheyenne, WY 82008-0007 ® Artwork courtesy of NASA URANUS WITH VOYAGER 2 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California As if a cosmic hand had reached out to inspire man's curiosity, Uranus alone among the planets rotates on its side. Were the Earth to rotate like Uranus, the North Pole would point due west. Passing Uranus in January 1986, Voyager 2 viewed this unique phenomenon, and made a number of other observations. Foremost were the first photographs of Uranus' rings, which appear to circle the planet vertically as they follow its strange sideways rota- tion. Uranus' moons take the same eccentric path; five were previously known and Voyager discovered ten more. Like those of its neighbor, Saturn, the Uranian moons are nearly half water ice. Voyager 2 revealed other fascinating facts: Uranus rotates once about every 17 hours; winds approaching 450 miles per hour roar around the planet; and Uranus emits intense ultraviolet radiation called “electroglow." Uranus is so distant that radio signals sent by Voyager took two-and-a-half hours to reach Earth. Yet the planet is barely half the distance from the sun to Pluto, the most distant outpost of the Solar System. No. 91-86 ©1991 The Maximum Card Collection A division of Unicover Corporation . Cheyenne, WY 82008-0007 ® Photograph courtesy of NASA NEPTUNE WITH VOYAGER 2 First Day of Issue: October 1, 1991 First Issue Location: Pasadena, California For centuries thought to be the planet furthest from the sun, Neptune is indeed that — but only sometimes. Pluto, usually most distant, has an extremely elliptical orbit that has brought it closer to the sun than Neptune — though only through 1999. In any event, Neptune is far away — more than 30 times Earth's distance from the sun. In fact, along with Pluto, Neptune is the only planet not visible with the unaided eye. Discovered independently in 1846 by British and French astronomers, the blue-green planet was named for the Roman god of the sea. Yet it is unlikely liquid water exists on this frigid planet, in many ways a virtual twin to Uranus. Neptune is accompanied by two moons, Nereid and Triton. Triton, the larger of the two, is unique to the Solar System in that it revolves backward, exactly opposite the rotation of its parent planet. This phenomenon has led astronomers to hypothesize ancient Neptunian satellites might have collided, leaving the two we see today in their strange courses around the mysteri- ous blue-green world. No. 91-87 © 1991 The Maximum Card Collection A division of Unicover Corporation Cheyenne, WY 82008-0007 ® Photograph courtesy of NASA