CAPTCHA or the Completely Automated Public Turing test to tell Computers and Humans Apart is widely advertised but one wonders if it is really useful or not. But, before we discuss its practical utility, let us see what CAPTCHA is all about. It is a test, which helps the computer to distinguish between machines and human beings. It creates and grades tests that automatically accept all humans and reject all machines.
It gives you a test to decipher distorted numbers and letters, which are pretty easy for a person to do, …

Like salt used as a preservative, high concentrations of dissolved minerals in the wet, early-Mars environment known from discoveries by NASA’s Opportunity rover may have thwarted any microbes from developing or surviving.
“Not all water is fit to drink,” said Andrew Knoll, a member of the rover science team who is a biologist at Harvard University, Cambridge, Mass.
Opportunity and its twin, Spirit, began their fifth year on Mars last month, far surpassing their prime missions of three months. Today, at a meeting of the American Association for the Advancement of …