Since our first close-up picture of Mars in 1965, spacecraft voyages to the Red Planet have revealed a world strangely familiar, yet different enough to challenge our perceptions of what makes a planet work. Every time we feel close to understanding Mars, new discoveries send us straight back to the drawing board to revise existing theories.
You would think that Mars would be easier to understand. Like Earth, Mars has polar ice caps and clouds in its atmosphere, seasonal weather patterns, volcanoes, canyons and other recognizable features. However, conditions on Mars vary wildly from what we know on our own planet.
Over the past three decades, spacecraft have shown us that Mars is rocky, cold, and sterile beneath its hazy, pink sky. We've discovered that today's Martian wasteland hints at a formerly volatile world where volcanoes once raged, meteors plowed deep craters, and flash floods rushed over the land. And Mars continues to throw out new enticements with each landing or orbital pass made by our spacecraft.
Among our discoveries about Mars, one stands out above all others: the possible presence of liquid water on Mars, either in its ancient past or preserved in the subsurface today. Water is key because almost everywhere we find water on Earth, we find life. If Mars once had liquid water, or still does today, it's compelling to ask whether any microscopic life forms could have developed on its surface. Is there any evidence of life in the planet's past? If so, could any of these tiny living creatures still exist today? Imagine how exciting it would be to answer, "Yes!!"
Even if Mars is devoid of past or present life, however, there's still much excitement on the horizon. We ourselves might become the "life on Mars" should humans choose to travel there one day. Meanwhile, we still have a lot to learn about this amazing planet and its extreme environments. NASA's latest mission to understand Mars is the Curiosity rover, which landed on Mars in August 2012.
Additional videos (Editor's note: Videos created by Rovio for Angry Birds Space Mars Update released on Nov. 1st.):
Red Planet: Curiosity's Cool Tools
Red Planet: Driving Miss Curiosity
Red Planet: Deciphering the History of Mars
Sojourner Mission Overview
Viking Mission Overview
Mars Exploration Rovers
Phoenix Mars Lander
MRO: Mars Reconnaissance Orbiter