Season 4 opens with an exploration of dying stars, the process where stars become supernovas, and, occasionally, become the biggest blast in the universe as a gamma ray burst (GRB). One death star, named WR104, lurks 8,000 light-years from Earth and some believe its GRB arrow is aimed directly at us. A death star galaxy named 3C321 is a frightening vision of what could one day befall the Milky Way galaxy: a companion galaxy's black hole being hammered with a constant blast of high-energy particles, wreaking havoc with its celestial bodies. Nearby, Death Stars Eta Carinae and Betelgeuse burn through their fuel supplies as they hurtle toward extinction...which just may be too close for comfort.

Without the moon, Earth would be a very different and desolate place today--four hours of sunlight with pitch-black nights, steady 100-mph winds spawning giant hurricanes that last for months, and virtually no complex life forms, much less humans. Safe to say, we probably owe our very existence to the moon. But what if it suddenly disappeared?

Every year, thousands of objects both natural and manmade plummet through our atmosphere and crash into the Earth. These menacing messengers from the sky provide scientists with amazing insights into the natural, and not so natural, phenomena of the cosmos. From space rocks crashing through homes to cosmic boulders triggering mass extinctions to rocket parts landing on front lawns, explore objects that fall from the heavens, such as asteroids, comets, meteor showers and space debris.

An examination of the most powerful explosions and blasts in the universe. Includes a look at the Mexico's Yucatán peninsula and the impact which caused the Chicxulub crater. Also a look at gamma rays and Big Bang Theory.

They are breathtaking, lethal and a constant source of surprise. The stunning rings of Saturn have mesmerized countless scientists over the centuries. With particles the size of a house shooting at 53,000 miles per hour around the planet, any spacecraft passing through would meet an instant and catastrophic end. Inside the rings is like a NASCAR race - with bumping, jostling and frequent collisions that can cause a massive spin-out. Lesser known are the other planets that have rings - Uranus, Jupiter, Neptune, possibly Pluto and Mars. Even Earth has a ring. Comprised of some 200 satellites in a geosynchronous orbit, it is the only known man-made ring in the universe. But the most remarkable thing about rings is that they contain the story of the birth of our solar system, and entire distant galaxies. Rings are more than a wonder of the universe - they reveal the secrets of our own origins.

Experts cook up ways you could destroy the Earth, including swallowing it with a black hole, blowing it up with anti-matter, hurling it into the Sun, and switching off gravity.

They are the one-stop-shopping places for learning all about the nature and variety of stars in the Universe. They're unique, because in clusters, all the stars were born at about the same time, from the same material and all are at the same approximate distance from Earth. This means we can be sure that any differences among them are due to their true natures and not distorted by different distances from Earth and other factors.

Outer space is already an essential part of America's ability to fight wars. Our military depends on satellites for many things, such as communications, reconnaissance and targeting information. But so far, no country has put weapons into space, although the U.S. and China have both shown they can shoot down satellites with ground-based missiles. If weapons do become a part of space, how will they work, how effective will they be, and what type of damage could they do? From ground-based lasers to telephone-pole sized rods hurtling from space at two miles per second to the far out weapons of the distant future, it's time to "lock and load" for Space Wars.

On alien planets, they rain from the sky as scalding iron. On distant moons, even at hundreds of degrees below zero, they slosh around in pristine lakes of methane. They can cover entire planets in miles-deep oceans of electrified hydrogen metal. Or erupt on alien worlds through miles-high geysers. They churn in the interiors of dead stars and even our own planet. They're so rare in the universe, they almost don't exist, but these are the magical liquids of our Liquid Universe.

They sort of sound like the same phenomenon, but Pulsars and Quasars are very different. Pulsars are tiny--only a few miles across--but they spin as fast as a kitchen blender and sweep the sky with beacons of radiation that make them appear to flash on and off. They have unbelievably strong magnetic fields, are more accurate than atomic clocks...and they can even tell aliens just where to find the Earth! Quasars are at the other end of the spectrum. Quasars are huge cores of galaxies with black holes that are called "monsters" and which spit lobes of radiating gas called "DRAGNs." Quasars are so far away, we see them as they were only in the distant past--meaning they existed only in the early universe, when they may have played a major role in the creation of the galaxies themselves.

Warp speed, transporters, wormholes and lasers--they are all staples of science fiction books, movies, and TV shows. But the fantastic world of tomorrow is quickly becoming the futuristic world of today. While you may not be "beaming" to your next appointment any time soon, researchers are preparing for the first tests of a present-day "transporter." And while scientists have long mocked Hollywood's visions of warp speed and faster-than-light travel as prohibited by Einstein's laws, a new generation of physicists continues to rewrite the fundamental rules of the universe. Is there a way around the cosmic speed limit? Maybe... as long as you're prepared to survive a journey through the ultra-high energies of one of the most violent places in the cosmos--the heart of a twisting, swirling vortex that leads either to strange, new worlds... or certain death.

Ours is a universe of energy, from powerful jets ejected from black holes to the raw nuclear fury of our Sun. But, the total amount of energy in the universe maintains perfect equilibrium--no more can be added or taken away. Because of this, there are enormous amounts of energy being transferred...electric, thermal, kinetic and magnetic energy are just a few that keep our universe balanced--and create awesome cosmic events and stellar displays.

The planets of our solar system have experienced epic catastrophes throughout their long history, both raining down from outside and bubbling up from within. We'll voyage back in time to investigate the violent events that profoundly shaped the planets, including earth itself. We'll witness stunning revelations about what transformed Mars into a barren, hostile desert...The disaster that changed Venus from temperate to hellish...The impact that blew away Mercury's mantle, turning it into a planetary core...A colossal disturbance that rearranged the orbits of the gas giants...Titanic impacts on Jupiter...And how a lost moon may finally explain Saturn's rings.

Could there be a monstrous, undiscovered star orbiting our own Sun? Could it be scattering killer comets throughout our Solar System like clockwork every 26 million years? New scientific surveys are probing the edges of our Solar System--a realm populated by giant worlds and mysterious planetoid--hunting for Nemesis, the Sun's purported evil twin. We may be on the verge of discovering this ultimate death star, suspected of causing every mass extinction in Earth's history. We employ everyday experiences to explain what Nemesis is and why it's been so hard to find. Experts start a wildfire on a dry California hillside, race a NASCAR around an oval track, and juggle fire, all in the effort to present how Nemesis works, and why life on Earth may depend on its discovery.

At 4.6 billion years old, the Solar System is our solid, secure home in the Universe. But how did it come to be? In this episode we trace the system's birth from a thin cloud of dust and gas. Shocked by a nearby supernova, the pull of gravity and natural rotation spun it into a flat disc from which the Sun and planets coalesced. It all happened in the space of 700 million years, during which the planets jockeyed for position, dodging the brutal bombardment of deadly asteroids and setting into the neat, stable system that we now realize might be a rarity in the universe.

What might happen if the first manned mission to Mars crashes hundreds of miles from the rocket that would take them back home? Could they survive the crash, and travel across the brutal Martian surface to their home ship? We'll show what the astronauts would have to do to survive dust storms and space radiation, while extracting vital resources like water from the Martian soil itself. It's a dramatic vision of the very near future, where survival can depend on pre-industrial technology and human ingenuity.

Earth may seem like the most hospitable planet in the solar system. But look again. Startling new discoveries reveal the blue planet has been plagued by more chaos and destruction than scientists once imagined. Stand on the Earth billions of years ago as a primitive planet slams into it. Shiver as our entire globe is frozen over like a gigantic snowball. Feel the heat as mammoth volcanoes scorch the landscape and darken the sky. From a cosmic gamma ray burst frying away the ozone layer to an Everest-size asteroid slamming into the ocean, we'll reveal new information about how these unparalleled events drove life to the brink of total extinction. Out of this continuous devastation, how has our planet--and life--got to where it is today? Are the worst days behind us--or lurking in the distant future?

Many argue that flying saucers and other extra-terrestrial space ships continuously visit the earth. If that were true, what kinds of technologies would such alien spacecraft require? And do eyewitness reports of UFO sightings jibe with modern theories of how interstellar travel might be possible? Authors, astronomers and theoretical physicists weigh in with the blueprints for inertia-canceling devices, nuclear-powered craft, antimatter propulsion systems and even warp drives. Based on Einstein's theories and countless scientific studies, we'll find out how these visitors might bridge the vast distances between the stars. And if they could survive such hazardous journeys, are they flesh and blood or intelligent machines?

To our ancestors, the appearance of certain astronomical events meant something big and something bad was coming. They were portends of death, plague, famine, or war. But what were they really seeing? And how did fear of these objects in the sky actually change the course of history?

Could the strange shapes of the universe solve the mysteries that have haunted mankind since ancient times? Is the eye of God peering at us from the heavens? What is the strange hexagon at the pole of Saturn, or the face on the Moon? Each shape tells its own story of an object's origin, and how physical forces shaped the Universe, and each is a chapter in the greater saga of existence.

Hell fires, endless winters, or a planet wracked by earthquakes are a few versions of Armageddon visualized by the Vikings, Aztecs, and the rest of our ancient ancestors. But which does modern science think will be closest to the truth? Celestial phenomena--the aging of our sun, the expansion of our universe, and other potentially cataclysmic events--could trigger the kind of Armageddon the ancients feared. Which ancient prophecy do scientists believe actually foretells our doom? And how close are we to the end of the world?

The ancients believed that the universe consisted of countless worlds we could not see, and argued endlessly over the nature of these distant, invisible planets and whether they might be inhabited. Until recently many scientists thought we would never discover the truth, believing that extra-solar planets were simply too far, too small and too dim to detect. But new technologies have suddenly revealed thousands of distant planets, opening up the most exciting period in astronomy in decades. Some believe we're on the verge of answering the ancient question: are we alone in the universe?

Do Rome's ancient monuments have secret connections to the Sun? New archaeological evidence, confirmed by NASA data and recreated in state-of-the-art virtual reality, suggests that early Roman emperors mastered architecture and astronomy to make the Sun create strange special effects for reasons both political and personal. One set up an obelisk and altar that blocked the Sun on the anniversary of Julius Caesar's murder, another built a domed room that bathed him in sunlight on certain days, and the Emperor Hadrian designed the Pantheon to mark cosmic events like equinoxes, and turned the central "oculus" of the temple dome into his own personal spotlight, but for what nefarious purposes? We uncover the last great mysteries of the ancient world's greatest empire. The answers are hidden in ancient ruins...and among the stars.

Scientists have no idea what it is, but Dark Matter and Dark Energy make up 96% of the Universe. Dark Matter is everywhere. It passes through everything we know on earth at billions of particles every second, yet no one has ever gotten a direct detection of this mysterious dark substance. An even more bewildering force is Dark Energy, which is rapidly pushing apart our Universe. Discovered only ten years ago, scientists are struggling to comprehend its unusual characteristics and answer the ultimate question; what is the fate of our Universe?

Does life exist on other planets? Astrobiology is a visionary new science that searches for life in space by combining the disciplines of astronomy, biology and geology. How did life evolve on Earth? What will life look like on other planets? These and other pertinent questions will be answered by a diverse group of scientists.