Mars has fascinated us for years. From the time astronomers first turned their telescopes on the planet shining in the night sky, we have imagined life there. Unlike our other planetary neighbor, Venus, which remains shrouded in cloudy mystery, the red planet has invited speculation and exploration. The U.S., the former Soviet Union, Russia and even Japan have launched spacecraft destined to land on or orbit Mars since the 1960s. Meanwhile, Earth-bound scientists keep their fingers crossed for more information about the red planet.
The successful missions, like the very first Mars flyby in 1964 by the U.S. Mariner 4, have provided a treasure trove of data and, of course, introduced many new questions. Recently, those data, compliments of spacecraft such as the Phoenix Mars Lander, the Spirit and Opportunity rovers, and the Mars Global Surveyor orbiter among others, have been arriving at Earth at a dizzying rate. It seems like a golden age for Mars exploration.
Here's what we've learned about the fourth planet from the sun while orbiting it, landing on it and sampling its contents: It's cold, dusty and dry, but that probably wasn't always the case. Ample data seem to point toward liquid water rushing over its surface in the form of lakes, rivers and an ocean at some undetermined point in the past. Traces of methane have been detected in the atmosphere, but the source is unknown. On Earth, much of the methane is produced by living organisms, like cows, which could bode well for the possibility of life on Mars. On the other hand, the gas could also have nonbiological origins, such as the Martian volcanoes.
One thing we do know: Humans won't be walking on Mars anytime soon. All manner of robots will be cruising its dusty surface long before we do, including possibly some inflatable, lightweight probes that will roll around and gather data.
The next best thing to exploring Mars is reading about it, right? So get ready for to launch into the fascinating world of the red planet. How did it form? What's the weather like? And most important, has water or life on Mars ever existed?
Read on to find out why early astronomers erroneously thought canals crisscrossed the planet, like an extraterrestrial Venice.