Dark Matter - Turns out most of the universe is held together by a mysterious, invisible substance.

Of Mice and Memory - Mice placed in enriched environments can recover lost memories, giving hope to those who study Alzheimer's.

Profile: Hany Farid - This self-proclaimed "accidental scientist" is a digital detective inventing new ways to tell if photos have been faked.

Wisdom of the Crowds - Ask enough people to estimate something, and their combined guesses will get you surprisingly close to the right answer.

Personal DNA Testing - Genetic testing to assess risk factors for a handful of serious illnesses is now commercially available. But is it a good idea?

Art Authentication - See how clever computer algorithms can distinguish a master fake from a masterpiece.

Capturing Carbon - An eighth-grader's science fair project prompts her scientist father to develop a new way to pull excess carbon dioxide out of the atmosphere.

Profile: Pardis Sabeti - By night she's a rocker. By day, she's a Harvard geneticist tracking the evolution of the human genome.

Saving Hubble - Two teams of spacewalkers take on the risky mission of reviving the ailing Space Telescope.

First Primates - Our most distant primate ancestors, which lived about 55 million years ago, were tree-dwellers the size of mice.

Profile: Alfredo Quiñones-Hinojosa -

He jumped the fence from Mexico to work as a farmhand and ended up a leading brain surgeon.

Killer Microbe - A relatively benign bug becomes a highly lethal pathogen, known to U.S. soldiers as Iraqibacter.

Leeches - A century after falling out of favor, medicinal leeches are back in hospitals, sucking away on patients' wounds.

SETI - Astronomers have their radio telescopes tuned to receive signals from alien worlds. But is anybody out there?

Stem Cells Breakthrough - Three separate teams overcome a biomedical hurdle—creating stem cells without the use of human embryos.

Profile: Edith Widder - Meet a marine biologist and explorer who has engineered new ways to spy on deep-sea creatures.

Phoenix Mars Lander - NASA's latest robot has already found frozen water and is looking for more signs that the Red Planet could support life.

Brain Trauma - Even so-called "mild" head injuries turn out to be anything but.

Mammoth Mystery - A pair of mammoth skeletons is found locked together by their tusks. What happened?

Profile: Judah Folkman - Once scorned for his ideas about how cancer grows, the late Judah Folkman is now hailed as a visionary.

Aging - Will research into "longevity genes" help us live longer and healthier lives?

Space Elevator - Can we build a 22,000-mile-high cable to transport cargo and people into space?

Maya - NASA archeologists use satellites to pinpoint ancient ruins buried deep in the jungle.

Profile: Bonnie Bassler - Her insight into how bacteria "talk" has launched a revolution in biological and medical research.

Mass Extinction - What caused the mother of all extinctions 250 million years ago?

1918 Flu - A virus that killed up to 50 million people is brought back to life to decipher its deadliness.

Profile: Cynthia Breazeal - A daring engineer designs robots to communicate and interact the way people do.

Papyrus - Scraps of writings from a garbage dump in ancient Egypt reveal what life was like 2,000 years ago.

Asteroid - Will a doomsday rock the size of the Rose Bowl hit Earth in 2036?

Island of Stability - Follow the decades-long quest to create the elusive element 114.

Obesity - Examine the biology behind the compulsion to eat.

Profile: Karl Iagnemma - An innovative MIT roboticist is also an acclaimed fiction writer.

T-Rex Blood? - Preserved soft tissue, including possible blood vessels and red blood cells, are turning up in dinosaur fossils.

Epigenetics - Our lifestyles can change the way our genes are expressed, leading even identical twins to become distinct as they age.

Kryptos - A coded sculpture at CIA headquarters has yet to be fully broken.

Profile: Arlie Petters - A boy from a rural village in Belize grows up to become a world-class mathematician and cosmologist.