Finding Life Beyond Earth Page #2

---

of information

of where life can exist

past the Earth and out

into the solar system.

NARRATOR:

So, where in our solar system

could life potentially exist?

Heading out from the sun,

the first planet is Mercury.

It's an extremely hostile

environment.

In March 201 1 ,

NASA's Messenger probe becomes

the first spacecraft to orbit

this small ball

of rock and iron.

These are some of the first

images sent back.

Three times closer to the sun

than Earth is,

Mercury bakes in 800-degree heat

on its side facing the sun,

while on the night side,

temperatures plummet

to minus 290.

Mercury is the ultimate

desert world.

Life of any kind here

seems unlikely.

Mercury's closest neighbor,

Venus, is almost as hostile.

Though nearly twice as far

from the sun,

temperatures here

exceed 880 degrees.

Decades of observations

have revealed

a planet shrouded

in carbon dioxide

and toxic clouds

of sulfuric acid.

These radar images reveal

thousands of ancient volcanoes

on a surface hot enough

to melt lead.

And with an atmospheric pressure

that is 90 times greater

than on Earth,

it is hard to imagine that

anything could live down here.

But based on chemical analysis

of the atmosphere,

scientists believe that water

once flowed on Venus's surface.

If life ever did exist here,

evidence has yet to be found.

So what is it about Earth, the

third planet out from the sun,

that makes life possible?

The answer lies

in three key ingredients.

First, all life is made up

of organic molecules

consisting of carbon in

compounds that include nitrogen,

hydrogen and oxygen,

among others.

Although organic molecules

aren't alive themselves,

they are the basic building

blocks of every living organism.

Life also needs a liquid,

like water.

In water, the basic organic

molecules can mix, interact

and become more complex.

The last ingredient is

an energy source like the sun

to power the chemical reactions

that drive all life,

from the smallest microbe...

to us.

When these three ingredients

came together

billions of years ago, life

found a way to take hold...

and today persists even in

the most extreme environments,

like here.

This is the Mojave Desert,

Nevada.

It is one of the hottest,

driest places on our planet.

McKAY:

This part of the desert is

particularly interesting to me,

because it's the driest part.

There's an axis of dryness here.

If we go either east or west,

it becomes wetter.

NARRATOR:

Surprisingly, even here, with

only a foot of rainfall a year,

all three ingredients

for life are present.

The rocks provide

just enough shade

to prevent water from

evaporating completely.

McKAY:

Underneath the white rocks,

Rate this script:0.0 / 0 votes