In many of its physical properties, Mars is similar to the Earth. Our neighboring planet is only about half the size of ours, but it has many Earth-like features, such as clouds, sediment layers, sand dunes, and volcanoes. Mars also has polar ice caps that grow and recede with the changing of the seasons. The tilt of the axis of Mars is 25°, just slightly more than the 23.5° of Earth, so that Mars also has seasons like Earth's. Martian days are almost the same length as the terrestrial day. The surface of Mars is scored by both wind and water erosion, strong evidence that liquid water flowed on its surface in the past. Mars’s uniquely wet past makes it a fascinating comparison with Earth, the only planet to currently have liquid water on its surface.
Orbital diagram of our solar system. Click here for original source URL
The similarities to Earth, and hints of a drastically different climate in Martian history, have made scientists wonder whether Mars harbors life, or perhaps did so in the past. Such questions have excited the imaginations of scientists and philosophers, as well as science fiction writers. They continue to inspire anyone with an interest in the "red planet."
This composite image of Earth and Mars was created to allow viewers to gain a better understanding of the relative sizes of the two planets. The Earth image was acquired from the Galileo orbiter at about 6:10 a.m. Pac. Click here for original source URL
Mars has always had an ominous mien in myth and culture. Ancient civilizations regarded the planet as a malevolent agent of war and apocalypse. Similar myths emerged around the world. In late Babylonian texts, Mars is identified with Nergal, the fiery god of destruction and war. To the Greeks, Mars was Ares, one of Twelve Olympians and the son of Zeus and Hera. His attendants on the battlefield were Deimos and Phobos, terror and fear, and his sister and companion was Eris, the goddess of discord. Ares was an important but an unlikable character. In Roman hands he morphed into a virile and noble god, one who facilitated agriculture as well as war. The third month of our year honors him and the time when winter abated enough that Roman legions could begin their military campaigns. In legend, Mars abandoned his children Romulus and Remus and the twins went on to found the city of Rome. The mystique of Mars may have been enhanced by its retrograde motion: the fact that every few years it twice reverses its direction of motion among the stars. All exterior planets show this behavior but the reversal is more dramatic for Mars than for Jupiter and Saturn. It�s curious that such a modest speck of reddish light could exert such power.
Scale model of the diameter of the planets. Click here for original source URL
Flash forward nearly two thousand years and Mars still exerts a grip on the imagination. It’s the night before Halloween, on the eve of the Second World War. Families across America are settling around the radio to hear "The Mercury Theater on the Air," a weekly program directed by the young Orson Welles and featuring him and a talented ensemble cast. Listeners are enjoying salsa-inflected orchestral music from a hotel in New York City when the announcer breaks in: "Ladies and Gentlemen, we interrupt our program of dance music to bring you a special bulletin from the Intercontinental Radio News." There's a news report about unusual activity observed on the surface of Mars, then back to the music. A few minutes later the announcer breaks in with additional information about Mars. More music. The next interruption has the announcer talking in breathless tones about a meteor that just landed in New Jersey. A little later, on the scene, there's horror in his voice as he describes creatures emerging from the meteor, which is in fact a spaceship. The Martians begin using a heat ray to incinerate bystanders, and as the announcer describes the engulfing flames, his voice is cut off in mid-sentence. Welles deliberately scripts several long seconds of silence, or "dead air," to increase the tension and the verisimilitude. In New Jersey and elsewhere around the country, people panic and many load their belongings into cars to escape the menace.
To the modern ear, Welles’ broadcast has the tone of cheesy, B-grade science fiction. But this was a younger, more innocent world, worried about war and ignorant about the improbability of aliens actually visiting Earth. It was nearly twenty years before America would enter the Space Age. In fact, the story of invasion from Mars transcends particulars of time and culture. When H.G. Wells’ novel "The War of the Worlds" was published in 1898, it was an instant classic. His words retain their evocative power: "Yet across the gulf of space, intellects vast and cool and unsympathetic, regarded our planet with envious eyes, and slowly and surely drew their plans against us." Over a century later, when Stephen Spielberg adapted the book for a 2005 movie, the basic plot was unchanged. Fear of alien invasion taps into something deep in the human psyche, as primal as dreams themselves.
Giovanni Cassini. Click here for original source URL.
Christian Huygens. Click here for original source URL.
Galileo Galilei. Click here for original source URL.