Bryce: This is the story of our Earth’s formation four-and-a-half billion years ago,
and of a little asteroid called Bennu, who’s also survived until now.
We have the team at NASA to thank for bringing us this video.
NASA narrator: The Milky Way, home to billions of stars, rising and setting over billions
of worlds, including our own.
In this vast expanse, how did our Sun, the Earth, and the planets come to be?
In recent decades, our understanding of the solar system’s evolution has greatly improved,
but deep questions remain.
To answer those questions, astronomers are preparing to visit someplace very small: asteroid
Bennu.
A lump of rock and organic material the early building blocks of the solar system—of Earth,
of us.
Bennu is a time capsule, and its journey takes us way, way back, four-and-a-half billion
years.
The raw ingredients of Bennu, and our solar system, originated in a stellar nursery—a
vast cloud of hydrogen, helium, and dust.
Our own sun doesn’t yet exist.
Nearby are hot stars like this one, quickly burning up its fuel and destroying itself
in a colossal explosion called a supernova.
The explosion destabilizes our cloud, causing it to collapse.
In the geologic blink of an eye, 100,000 years, gravity and angular momentum flatten the cloud
into an exploding disc.
In the center, where molecules crash together tightest, a protostar revs up to incredible
pressures and temperatures.
Deep within the disc, clumps of dust not much larger than a grain of wheat are flash-heated
into droplets of molten rock called chondrules.
The source of this heat remains a mystery.
Chondrules are destined to become the building blocks of the solar system.
Coaxed by gravity and turbulence, the chondrules clump.
They grow into the first asteroids, into mountains, into planets.
The asteroids are rubble piles of rock, metal, ice, and organics.
This large asteroid is the parent body of Bennu, a protoplanet whose size we can only
guess.
Closer to the protostar a planet begins to form.
And then, dawn in the solar system.
The protostar undergoes fusion and ignites, revealing our sun, but the solar system is
far from finished.
Jupiter most-likely forms near its outer edge.
But just 500 million years after the sun ignites, some believe that it slowly moves inward,
its massive gravity ripples the asteroid belt, disrupting countless asteroids and comets,
flinging them toward the sun.
They rain down on the inner planets, hammering and remelting large portions of their crust.
Did these impacts also deliver organics in water, key ingredients for life.
Back in the asteroid belt, Bennu’s parent body is lucky, it survives this period of
heavy bombardment.
The solar system cools and calms.
Jumper and its many moons assume the orbits that we see today.
Billions of years of quiet follow, more or less.
Then a billion years ago, one theory suggests, a collision shatters the protoplanet.
Some of the debris loosely coalesces into a new smaller body: Bennu.
But Bennu will not stay in place.
Dull, non-reflective, it slowly migrates toward the sun.
Solar heating turns its warm side into a glowing low-intensity thruster.
Through millions of years, Bennu’s orbit gradually tightens until it interacts with
Saturn’s gravity, altering its trajectory and hurling it into the inner solar system.
Close encounters with Earth and Venus follow.
Their gravitational tugs may have repeatedly stretched and reformed Bennu, turning it inside-out
and pulling off loose material.
As a result, it has no satellites of its own, until now.
Today, NASA is sending a spacecraft called Osiris Rex to explore Bennu and retrieve a
sample.
Why?
Bennu has survived its long journey and settled into a near-earth orbit, bringing its secrets
within our reach.
Now it is ready to teach us more about the solar system’s history, its formation, its
evolution, and our own place among the stars.