By Dr David Whitehouse
BBC News Online science editor

Dark streaks on crater and valley walls may indicate that brackish water currently flows across the surface of Mars.

New images and analysis suggest the slopes around the Red Planet's largest extinct volcano, Olympus Mons, contain dark stains caused by brine flowing down hill.

The discovery indicates that the substantial underground ice deposits on Mars can sometimes melt and flow across the surface.

It is bound to increase speculation that life may exist near to the surface of the planet.

Sub-Urban Renewal
Thanks to new tunneling technologies, real estate trends are down. Way down.
By Fred Hapgood

It's the mantra of every silver-tongued real estate agent straining to close a deal: They're not making any more land. But imagine if they were. Suppose acres of new land could be manufactured just like I-beams, bolts of cloth, or toothpaste. And what if this man-made frontier could be rolled out anywhere, even in the heart of the densest metropolis, without displacing anyone?

Well, it can. The world's cities may be overcrowded, and the suburbs that surround them may be choked by unchecked sprawl, but there's plenty of undeveloped space. It's right at your feet: underground. There are 100 quadrillion cubic feet of undeveloped metropolitan real estate in this country alone, and that's counting just the first mile down. Think of it this way: If everyone in the entire country moved to Los Angeles, each of us could have 2 million cubic feet to house our stuff. How does that compare with where you live now?