But almost 40 years of robotic exploration have revealed a fascinating world of deep valleys and huge, extinct volcanoes, and where ice-crystal clouds sometimes linger in a salmon-pink sky. So the attraction remains. The environment may be inhospitable, but it is far more welcoming than the searing surface of Venus. And the question of Martian life is still far from settled. Mars is dry today. But spacecraft photographs — the entire planet has been mapped from orbit — show that water once flowed on its arid surface.
There are many etched river valleys and boulder-strewn flood plains that have no other easy explanation. Analysis from orbit and from rover missions have found minerals that form only in the presence of water. Clearly, Mars was once much warmer. Even if the planet bears no life today, it may have done so in its youth.
There may be more than just fossils, too. For years, planetary scientists have been asking: where did all that water go? Much of it probably evaporated into space but there is evidence that some at least is still there, underground.
Perhaps humans will one day join robots on the red planet. NASA has stated its goal to send humans back to the moon as a stepping-stone to Mars. Will humans eventually build a scientific base on the Martian surface, like those that dot Antarctica? How will human activity affect the red planet or our searches for life there?
Time will tell. But no matter what, Mars will continue to occupy the human imagination, a glimmering red beacon in our skies and stories. All rights reserved. Mars Nearing Earth In , the Hubble Space Telescope snapped this photo of the red planet 11 hours before its closest approach to Earth in 60, years.
Longer year and shifting seasons With a radius of 2, miles, Mars is the seventh largest planet in our solar system and about half the diameter of Earth.
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Science Why it's so hard to treat pain in infants. This explanation dates back to a study by David Rubie and colleagues at the University of Bayreuth, Germany. The second reason for Mars' redness is its atmosphere. Scientists found that Mars' atmosphere at the surface consists of 95 percent carbon dioxide, 2.
Mars' atmosphere appears red because so much of the planet's iron oxide dust gets blown around in enormous storms. These dust storms occur every year, and some are so big they cover areas the size of continents and can last for weeks at a time. Some, which are more rare, circle the entire planet and have caused NASA rovers to stop working.
Another reason Mars' atmosphere looks red is more complicated, and involves the way sunlight reflects off of the planet. Mars' atmosphere is thinner than Earth's, which is one reason why humans wouldn't be able to survive there without a spacesuit. Due to this thin atmosphere, sunlight that is reflected away from Mars appears red due to a phenomenon known as Rayleigh scattering—or the lack of it. Rayleigh scattering occurs when light hits particles that are smaller in size than the wavelength of that light, such as gas particles in the Earth's atmosphere.
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