-
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.