How does light escape from the sun? We take a journey from the center of the sun, following the path of light. We witness its fiery birth from in the core, its 430,000 mile battle against gravity and magnetism, and its escape from the solar surface.

Drazen Petrovic and Vlade Divac were two friends who grew up together sharing the common bond of basketball. Together, they lifted the Yugoslavian National team to unimaginable heights. After conquering Europe, they both went to America where they became the first two foreign players to attain NBA stardom. But with the fall of the Soviet Union on Christmas Day 1991, Yugoslavia split up. A war broke out between Petrovic's Croatia and Divac's Serbia. Long buried ethnic tensions surfaced. And these two men, once brothers, were now on opposite sides of a deadly civil war. As Petrovic and Divac continued to face each other on the basketball courts of the NBA, no words passed between the two. Then, on the fateful night of June 7, 1993, Drazen Petrovic was killed in an auto accident. "Once Brothers" will tell the gripping tale of these two men, how circumstances beyond their control tore apart their friendship, and whether Divac has ever come to terms with the death of a friend before they had a chance to reconcile.

The Indian Ocean is the third largest body of water on Earth at more than 6,000 miles wide and covering 13% of the world's surface. It is home to 5,000 species of fish, many of which only exist in the Indian Ocean. But it is also an ocean under threat from global issues such as over-fishing and climate change, which make this an ocean on the edge.

Around 30% of the land's surface is desert, the most varied of our ecosystems despite the lack of rain. Unravel the secrets of desert survival and experience the ephemeral nature of this dynamic environment. Watch Saharan sandstorms nearly a mile high and desert rivers that run for a single day. In the Gobi Desert, rare Bactrian camels get moisture from the snow. In the Atacama, guanacos survive by licking dew off cactus spines. In the USA, the brief blooming of Death Valley triggers a plague of locusts 65km wide and 160km long. A unique aerial voyage over the Namibian desert reveals elephants on a long trek for food and desert lions searching for wandering oryx.

In the last few years, the Red Planet has yielded up many new clues that life may have once existed there...and may even exist there today. There is now have proof that water once flowed on the surface, that Mars once had lakes, and that the frozen poles are mostly water, not carbon dioxide as previously thought. Mars has snow--an aurora--and lightning generated by dust storms. Most intriguing of all are the seasonal plumes of methane that just may point to bacteria living below the surface.

Invertebrates don't always operate alone. True society was the last feature to evolve in invertebrates, as recently as the time of Tyrannosaurus. In the last programme see the tensions below the surface in some of the great social structures built by insects, and witness the carnage when an ant colony and a termite colony wage war.