A series of satellite photographs taken by NASA's Mars Global Surveyor, which has been mapping Mars since 1999, raise the exciting possibility that liquid water may have existed there very recently.

Earth's water is in constant motion. It cycles through the planet's atmosphere, surface, and depths. This water cycle is fundamental to Earth’s climate — and is being dramatically affected by global warming.

Rocks older than 4 billion years are not available to study, making the first 500 million years of Earth's history particularly mysterious. But cutting-edge techniques are now allowing geologists to study survivors of Earth's early era.

In 1912, Viktor Hess took to the sky in a hot-air balloon and discovered a radioactive energy now called “cosmic rays.” Travel to Argentina to see how scientists now hope to discover at long last where the highest-energy cosmic rays are coming from.

The ring-tailed lemurs that romp around the research camp at the Beza Mahafaly Special Reserve in southwest Madagascar spend plenty of time behaving badly. The same isn't true for their counterparts in the wild.

The lemurs of Madagascar, the most diverse group of primates in the world, had even more members in their ranks before humans first arrived on the island two millennia ago — 16 of the perhaps 70 species aren’t around anymore.

Mapping one-quarter of the heavens in three dimensions — that’s the ambitious mission for the Sloan telescope at the Apache Point Observatory in the Sacramento Mountains of New Mexico. Find out what astronomers have discovered so far.

Vietnam harbors an astonishing range of habitats, from rain forests and dry forests to mangroves and coral reefs. It's also home to an unusually rich array of plants and animals. Find out why.

Millions of gallons of water flow through New York City’s water system each day. Where does it all come from? And where does it all go? Take an interactive journey to find out.

Focus on the best books about astronomy, astrophysics, light, telescopes, digital imaging, and the 3-D universe with this list of recommended titles, suitable for older students and adults.