Seven Wonders of the Rocky Planets and Their Moons
This false color image uses color to show the different elevations on the Martian surface Olympus Mons is the large silver area Seven Wonders of the Rocky Planets and Their Moons During the four hundred years since 1610 when astronomers first studied Mars through telescopes no one suspected that Mars had such a huge mountain Astronomers thought that Mars was a much older world than Earth They thought that if it had ever had high mountains they would have long ago eroded worn down by wind and water They expected Mars to be a world of flat dusty deserts with a few low rolling hills In 1971 the Mariner 9 spacecraft went into orbit around circled Mars It took the first good close-up photos of the planet Scientists were disappointed by these first pictures The clouds of a vast dust storm buried the surface of Mars The planet looked as featureless as a tennis ball Then scientists noticed four dark spots in the blank cloud cover They realized that the spots must be the tops of vast mountains To rise above the dust cloud these mountains had to be higher than any others then known in the entire solar system Hints of craters in the centers of the spots suggested that all four mountains might be enormous volcanoes FACTS ABOUT 141 million miles 228 million km Mars Diameter width 7,520 miles 12,103 km Average Distance from the Sun Length of Year 687 Earth days Length of Day 1,029 Earth days 10
The MounTains That Weren’t There Astronomers thought that if Mars had mountains they would likely have snow on their peaks just as the highest mountains on Earth do The snow would look like tiny bright spots through the astronomers telescopes Sure enough astronomers discovered several small bright spots near the south pole of Mars These spots appeared in the same place year after year so astronomers thought that they were the tops of mountains They named them the Mountains of Mitchel below after Ormsby Mitchel the astronomer who first saw them in the first half of the nineteenth century But when the first space probes visited Mars they found no mountains at the south pole The famous Mountains of Mitchel turned out to be large patches of white frost that be large patches of white frost that appear every year in the same place appear every year in the same place Top Mariner 9 was the first spacecraft to take good close-up photos of Mars Bottom This Mariner 9 photograph from 1971 shows Olympus Mons standing above a dust storm on the Martian surface
Olympus Mons is so big it would be impossible for an astronaut to see it from the surface of Mars It would be like trying to see the entire Rocky Mountain chain or the Great Lakes from one spot on the ground William K Hartmann American astronomer 2003 Once the dust settled the probe took better photos Astronomers realized that they had been right The four mountains were huge volcanoes They were the biggest mountains of any kind in the solar system how They CaMe To Be Olympus Mons and its neighboring volcanoes are fairly young compared to the rest of the surface of Mars They are about 1 to 3 billion years old The volcanoes sit atop the Tharsis Bulge This is a vast bulge on the surface of Mars Olympus Mons upper left lies on the left of the Tharsis Bulge On the right side of the Tharsis Bulge lie three more large volcanoes
It is about 6 miles 10 km high and about 5,000 miles 8,000 km wide Although the bulge is huge you would never notice it if you were standing on it It is almost one thousand times wider than it is high so the angle of its slope is very small The Tharsis Bulge covers one-quarter of the Martian surface A huge column of molten rock beneath the surface pressed on the crust of the planet to create the bulge Similar places on Earth are called hot spots The country of Iceland sits above one of these Yellowstone National Park in Wyoming sits above another The Hawaiian Islands form from another hot spot on Earth Volcanoes have formed above these hot spots on Earth just as they have on the Tharsis Bulge The hot spot on Mars may have cooled millions of years ago The volcanoes above it may no longer be erupting lava The volcanoes on Mars are much bigger than those on Earth Earth’s crust is made of many stiff rocky plates These are like rafts drifting on the softer hot material that lies beneath Mars’s crust doesn’t have separate plates Its crust is much more rigid than Earth’s The crust of Mars can crack and shift but it cannot float and drift the way the plates on Earth do Olympus Mons Because Mars does not have a moving crust its volcanoes tend to sit on top of their hot spots forever This means that lava and ash just kept pouring out building up layer after layer This is why Olympus Mons is nearly two and a half times taller than Mauna Loa and many times wider and more massive 13 HOT Spots On Earth hot spots tend to stay in one place while the surface crust moves above them So a volcano will stay active only as long as it stays above its hot spot If the crust moves it away from the heat the volcano will cool The chain of volcanoes that form the Hawaiian Islands is the result of the crust moving over a single hot spot As the crust moves a new volcano forms and its lava creates an island Currently the island of Hawaii is over the hot spot Eventually the island will move away from the hot spot and the volcano will slowly die It will join the other extinct volcanoes in the island chain Meanwhile a new volcano will take its place One is already beginning to form just off Hawaii’s eastern coast
