Secret Mars 
We probably know more about Mars than any planet other than our own -- the result of five decades of exploration. Even so, Mars yields its secrets slowly -- and still keeps quite a few.
For decades, for example, scientists thought the planet’s polar ice caps were made mainly of carbon dioxide, with only a small amount of water. In recent years, though, better observations have shown that it’s the other way around -- there are thick caps of frozen water, with smaller caps of carbon dioxide atop them.
In fact, there’s a lot more water on Mars than anyone had expected. Large amounts of ice are mixed with the Martian dirt, icy clouds float across the sky, and pockets of liquid water may hide below the surface -- one of the secrets that probes are still trying to uncover.
The biggest secret of all is whether anything lives on Mars today, or did in the past. There’s no evidence of large lifeforms -- we haven’t seen anything crawling across the surface or flapping through the sky.
But conditions on Mars were much more hospitable in the planet’s past, raising the possibility that microscopic life could have inhabited the planet -- and its descendants could still lurk in caves or other protected environments. It may take many more decades to unlock that biggest secret of all.
Look for Mars low in the east as darkness falls, and soaring high across the south during the night. It looks like a brilliant orange star. More about Mars tomorrow.
Script by Damond Benningfield, Copyright 2012