Segments in this Video

Forming Inner Worlds (04:10)


Over four billion years ago, the sun was surrounded by gas and dust leftover from its formation; gravity drew the debris together, forming planetesimals. Earth was the only planet that retained liquid water and evolved life, but other bodies were or may become habitable.

Exploring the Smallest Planet (05:18)

The Messenger Mission controlled its trajectory into Mercury’s orbit by using planetary gravity. It mapped its surface; images and data revealed features indicating a violent past and formation much further from the sun than current location.

Shoved Into Place (05:23)

Scientists theorize that Mercury formed 100 million miles from its current position, in a region where many planetesimals evolved and competed for space; they believe a larger body pushed it off orbit and pulverized its rocky crust.

No Living Conditions (05:07)

Scientists expected Venus to be habitable and contain liquid water. In 1982, Venera 13 collected data from the planet, proving it inhospitable. Atmospheric studies have shown it was once wetter and cooler.

Becoming the Hottest Planet (06:47)

Over four billion years ago, Venus was an ocean world with a temperate climate. Over two billion years ago, volcanic gases and a warming, expanding sun caused a runaway greenhouse effect; its water evaporated and its surface heated to 855 degrees Fahrenheit.

Once Habitable (03:02)

Data from Mars showed signs of liquid water. The planet’s small iron core generated gravity too weak to retain its original atmosphere; its magnetic field shut off as it cooled, exposing the surface to radiation, and evaporating its oceans.

Solar Life Cycle Impacts (05:41)

Earth currently receives the correct radiation to support lifeforms. Scientists predict the sun’s expansion will upset weather patterns, killing plants and the planet’s oxygen source. In a billion years, carbon dioxide will comprise the atmosphere as it is nearly engulfed by the growing Red Giant.

Cassini Huygens Mission (09:03)

As the sun dies, the solar system’s habitable zone will move out. An investigation of one of Saturn’s moons reveals a rocky, icy terrain with liquid methane oceans. Titan is too cold to host life, but supporting elements are present.

Potential for Life (02:03)

In more than five billion years, Titan and the outer planets of the system will receive more solar energy from the expanding sun. Its frozen water may melt and replace the liquid methane as it evaporates, creating a livable habitat.

Future Habitats (02:02)

The sun creates dynamic zones of habitability within the solar system during different stages of its lifecycle. Recent discoveries suggest the universe if full of potential life-hosting planets.

Credits: Inner Worlds (00:51)

Credits: Inner Worlds

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Episode 1: Inner Worlds (NOVA: The Planets)

Part of the Series : NOVA: The Planets
3-Year Streaming Price: $169.95



The rocky planets were born of similar material around the same time. Yet only one of them supports life. Were Earth's neighbors always so extreme and is there somewhere else in the solar system life might flourish?

Length: 53 minutes

Item#: BVL191990

Copyright date: ©2019

Closed Captioned

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