Humans have observed comets 
for thousands of years

as their orbits have brought them within
visible distance of Earth.

Appearing throughout historical records,

these mysterious lights that 
came out of nowhere

and disappeared after a short while

were thought to be ill omens of
war and famine,

or the wrath of gods.

But recent research has revealed that
comets may be even more deeply connected

to humanity and our presence on Earth

than any of these mythical 
explanations suggested.

When you think of our Solar System,
you probably imagine the nine,

sorry eight, planets orbiting the Sun.

But beyond Neptune,
far from the heat of the Sun,

there is a sparse ring found 
formed by icy chunks

ranging from the size 
of marbles to that of small planets.

And thousands of times farther at the
outer reaches of the Solar System

lies a spherical cloud of small 
fragments and gases.

Many of these ancient clumps of stardust
are leftovers from the formation

of the Solar System 4.6 billion years ago,

while some of the most distant may even
come from a neighboring system.

But sometimes the gravity from 
passing planets or stars

pulls them toward our sun,

beginning a journey that can take up to
millions of years.

As the frozen object travels further
into the Solar System,

the sun grows from a distant spark
to an inferno,

melting the ice for the first time
in billions of years.

Gas and steam eject dust into space,

forming a bright surrounding cloud,
called a coma,

that can grow even larger than
the sun itself.

Meanwhile, the intense stream of 
high-energy particles

constantly emitted by the Sun,
known as the solar wind,

blows particles away from 
the comet's core,

forming a trail of debris up to millions
of miles long.

The ice, gas and dust reflect 
light glowing brightly.

A comet is born, now orbiting the sun
along with the rest of the objects

in our Solar System.

But as the comet travels through
the Solar System,

the solar wind tears apart and recombines
molecules into various compounds.

In some of the compounds that
scientists found,

first in the rubble left by a meteorite
that disintegrated above northern Canada,

and then in samples collected by a space
craft from a passing comet's tail,

were nothing less important than
amino acids.

Coming together to form proteins
according to the instructs encoded in DNA,

these are the main active components
in all living cells,

from bacteria to blue whales.

If comets are where these building blocks
of life were first formed,

then they are the ultimate source of
life on Earth,

and, perhaps, some of the other places
they visited as well.

We know that planets orbit nearly every
star in the night sky,

with one in five having a planet
similar to Earth in size and temperature.

If Earth-like planets and the molecules
found in DNA are not anomalies,

we may be only one 
example of what's possible

when a planet under the right conditions
is seeded with organic molecules

by a passing comet.

So, rather than an omen of death,

the comet that first brought 
amino acids to Earth

could have been a portent of life,

a prediction of a distant future,
where creatures of stardust

would return to space to find 
the mysteries of where they came from.