People like to make lists of things, especially lists of superlatives: the best, fastest, oldest, largest, heaviest and so on. There are lists of the ten fastest animals and the ten longest rivers and even of the ten highest-paid rock stars. The Guinness company created a small industry from publishing lists exactly like these, and the fact that the Guinness Book of World Records has been published for more than fifty years just goes to show how popular they have been. But there's nothing new about compiling lists like these. The Greek historian Herodotus invented the first list of the "Seven Wonders of the Ancient World" around the fifth century BC.
Later Greek historians came up with their own lists of what they considered the greatest monuments of all time. For example, Callimachus of Cyrene compiled a list called "A Collection of Wonders Around the World"—though we'll never know what he included since it was destroyed when the great Library of Alexandria was burned. By the Middle Ages a kind of "official" list of Seven Wonders of the Ancient World had evolved. This included the Great Pyramid at Giza, the Hanging Gardens of Babylon, the stature of Zeus at Olympia, the Temple of Artemus at Ephesus, the Mauseoleum at Halicarnassus, the Colossus of Rhodes and the lighthouse at Alexandria. Only a few of those still existed at that time. Today, only the Great Pyramid remains.
The Ancient Wonders of the World were all created by human beings, so lists of the Seven Natural Wonders of the World seemed appropriate. Some wonders are so spectacular—such as the Grand Canyon—that they make everyone's list. Topping most lists of the world's natural wonders are the Grand Canyon, Mount Everest, the Great Barrier Reef, Victoria Falls, the Northern Lights, Rio de Janeiro Harbor and the Mexican volcano, Paricutin—though anyone might easily create their own list of seven after a few minutes' thought.
But what about the rest of universe? Our planet earth shares the solar system with many other worlds. This opens up many millions of square miles of additional territory in which there must surely lie new, unexpected natural marvels. And indeed there are.
Mars, in spite of the fact that it is only a third the size of the earth, has more land area than the earth—this is because three-quarters of our planet's surface is covered with water. And Mars has not wasted much of this territory on uninteresting landscapes. The little planet boasts the single largest volcano in the solar system—Olympus Mons. If transplanted to the earth, this monster mountain would cover the state of Nebraska and tower ten miles higher than Mt. Everest. It also has the largest canyon system, the incredible Vallis Marineris—which is four times deeper than the Grand Canyon and so long that it would stretch across the United States from coast to coast. And these aren't the least of the wonders to be found on Mars.
Not only are there other planets—Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto (which is so strange it may qualify as a natural wonder all by itself)—there are more than a hundred moons, some of them larger than the smallest planets. Some of the weirdest, most impressive sights in the solar system can be found on these little worldlets.
Listing the seven wonders of the solar system—and the many runners-up—is not a trivial thing to do. It helps us realize that the worlds we share the solar system with are places, with landscapes no less interesting than the ones on our own planet. It also helps us realize that the earth is not unique: it is part of a great family of worlds. Understanding how and why the other planets in the solar system resemble Earth, and how and why they might be different, helps us to better understand our own planet. It is much the same way that you understand your friends better if you know their brothers and sisters, mothers and fathers. The earth is also part of a family. It was born at the same time as the other planets in the solar system, and was formed from many of the same materials. Like a family of nine children, the earth shares many features and qualities with its planetary brothers and sisters. And like a human family, some of the children may be nearly identical, such as Venus and the earth, while others may hardly resemble one another at all. But because they all share the same parentage, there will be features common to them all. Understanding how the other planets came to be the way they are helps us to better understand our own planet earth.
Choosing the Wonders
What, I once wondered, would be on the postcards sent back to the earth by future space travelers? Over the years, I put that question to a great many people: astronomers, astronauts, science fiction authors and my fellow space artists. The answers were as diverse as the people offering them. The late Carl Sagan, for instance, thought that life on the earth would count for all seven. "The ready answers," he said, "—Olympus Mons, the rings of Saturn, the active volcanoes of Io, the water oceans of the earth, the putative hydrocarbon oceans of Titan, etc.—are trivial . . . I would say that all seven wonders should be drawn from the biology of the earth, with humans only one example of a wide variety of . . . wonders." Sagan was undoubtedly perfectly correct, but it seemed unfair to include our planet since it had already provided subjects for so many lists of wonders. It seemed more in the spirit of things to limit the choices to off-world places. Besides, including the earth would have seemed like voting for oneself in a beauty contest.
All in all, more than seventy different "wonders" were suggested. The hands down winner for the number one spot was (to no one's surprise) Saturn's Rings. Everyone seemed to agree with science fiction author Ben Bova in that they are "beautiful and mysterious."
The giant Martian volcano, Olympus Mons, received second place. "The only mountain we know of," wrote space artist/scientist Dan Durda, "that basically pokes its way entirely out of a planet's atmosphere."
Third place went to Jupiter's Great Red Spot, "a storm," Bova pointed out, "larger than the entire planet Earth that has been raging across the face of the solar system's largest planet for at least four hundred years."
Another feature on Mars won the fourth position. This was Valles Marineris (shown at the top of this page) a canyon as long as the United States is wide and up to 4.3 miles (7 km) deep. The fifth Wonder was the incredible volcanism of Jupiter's moon Io, the most volcanically active body in the solar system, and specifically the super-volcano Pele, probably the most powerful anywhere.
Sixth and seventh places were all ties. These included (among many other candidates) the ice spires of Callisto, which look like something from the cover of a 50s science fiction magazine; Verona Rupes a great cliff on Miranda, a tiny moon of Uranus; the weird sunrises and sunsets of Mercury; the equatorial mountain range on Iapetus; the asteroid Hektor; Herschel Crater on Mimas; the methane seas of Titan; and, of course, the fabulous geysers of Enceladus.
What would your choices be for the Seven Wonders of the Solar System?
Art by Ron Miller