Asteroid Bennu is a lump of rock and
organic material, the early building
blocks of the solar system, and Earth.
The raw ingredients of Bennu and our
solar system originated in a stellar
nursery billions of years ago. In a
colossal explosion of a supernova, clumps
of dust not much larger than a grain of
wheat were flash heated into droplets of
molten rock called chondrules. Chondrules
were destined to become the building
blocks of the solar system. They grew
into the first asteroids and into
planets. Asteroids are rubble piles of
rock, metal, ice and organics. One large
asteroid, a protoplanet, was the parent
body of asteroid Bennu. Then a billion
years ago a collision shattered Bennu's
parent. Some of the debris loosely
coalesced into a new smaller body which
became Bennu. Bennu had a dull
non-reflective surface causing it to
slowly migrate toward our sun. Through
millions of years, Bennu's orbit orbit
gradually tightened. Close encounters
with the Earth and Venus followed. Their
gravitational pull repeatedly stretched,
tore off loose material, and reformed Bennu.
Bennu is nearly spherical and
is quite accessible thanks to its
relatively Earth-like orbit. Bennu
completes one lap around our Sun every
14 months or 1.2 years and comes into
Earth's neighborhood hood every six years.
The orbit is inclined by just six degrees
compared to that of Earth.
Bennu has a very dark, black surface,
the color of coal that scientists think
indicates high concentrations of carbon
and hopefully a form of organic
materials that could date back to the
origins of the solar system some
4.5 billion years ago.
Bennu is a time capsule that could help
explain how life began on Earth. So
scientists hope to bring back a pristine
sample of the early solar system and
determine if asteroids like Bennu
delivered organic material and water to
the surface of the earth creating
habitability and the origins of life on
Earth. Bennu is shaped like a ball,
with a fat middle. Scientists believe the
bulge at the equator is made of loose
rubble or gravel and is ideal for
collecting a sample. Bennu is nearly
1650 feet in diameter
taller than the Empire State Building
and it rotates every 4.3 hours
so a day on Bennu is just
over 4 hours. It rotates slowly enough
to allow contact. Bennu was discovered
in 1999 and was known as 1999 RQ36.
14 years later it was renamed Bennu after
the Heron of Egyptian mythology, Bennu.
It is the best understood
near-earth asteroid that has never been
visited by a spacecraft. Bennu is
classified as a potentially hazardous
asteroid, and there's a slight chance it
could slam into the Earth. In 2135 the
asteroid will make its closest brush
with us, swinging by Earth about
220,000 miles away.
That's closer than the moon, which orbits
about 240,000 miles from Earth. But
chances of a collision happening are
just one-tenth of 1%. A trip to Bennu
will allow researchers to fine-tune
their understanding of Benny's orbit and
any threat it may pose to Earth.
Near-earth asteroids like Bennu
do pose a potential danger to our planet,
so it's important to predict their
orbits with great accuracy. It is
difficult however to make these
predictions over long periods of time.
One force acting on the orbits of
asteroids comes from the solar energy
that asteroids absorb and then radiate
away is heat, in a phenomenon known as
the Yarkovsky effect. When sunlight
strikes of rotating asteroid, the dayside
heats up. As the asteroid turns, the
nightside cools and releases the energy
as heat acting kind of like a mini
thruster that can change the asteroid's
direction over time. If you want to be
able to predict where an object like Bennu
is going to be in the future, you
have to account for this phenomenon.
So why travel to an asteroid? Over the last
100 years human population on the Earth
has exploded from about 1.5 billion
to more than 7 billion people,
driving an ever-increasing demand for
resources. To satisfy civilization's
appetite, communities have expanded
recycling efforts while mine operators
must explore forbidding frontiers to
seek out new deposits, opening up mines
deep underground or even at the bottom
of the ocean. Asteroids could one day be
a vast new source of scarce material.
Asteroids are lumps of metals, rock, dust
sometimes laced with ices and tar,
which are the cosmic "leftovers" of the
solar system's formation. There are
hundreds of thousands of them ranging in
size from a few yards to hundreds of
miles across.
Some asteroids have high abundances of
water bound up as hydrated clay minerals.
Currently these asteroids have little
economic value since water is so
abundant on Earth but they will be
extremely important if we decide we want
to expand the human presence throughout
the solar system. Their water content
could be broken apart into hydrogen and
oxygen which could be used as
rocket fuel.
This could enable fuel depots out there
where our mining these asteroids.
Some asteroids also have a lot of organic
carbon, phosphorus and other key elements
for fertilizer for astronauts to grow food.
Other asteroids have very little
water but contain a significant amount
of iron, nickel and cobalt as well as
gold, platinum, and rhodium. It currently
however cost hundreds of millions if not
billions of dollars to build and launch
a space mission, so innovations that
would make these costs fall dramatically
are needed before it is profitable to
mine asteroids for the value of their
metals alone. Because of our lack of
experience with mapping and analyzing
the resources and asteroids and to
extract material from them missions like
Osiris-Rex may help us to gain this kind
of critical information. Launched by nasa
on September 8, 2016 and rendezvousing
with Bennu in August of 2018
Osiris-Rex will study the asteroid in
detail, retrieve a sample, and return it
to Earth. The study will give researchers
insight into Bennu's orbit and
composition as well as develop important
technologies for asteroid exploration
and possible mining of them. Since being
launched by NASA in September 2016,
Osiris-Rex has entered a deep-space
orbit around our sun.
It will travel along this orbit for a
little over a year. In September 2017 one
year after launch,
Osiris-Rex, at its farthest distance from
the Sun, will perform a deep-space
maneuver to aim for Earth to make a
gravity assist flyby of Earth.
It will use Earth's orbital energy to
slingshot the spacecraft farther into
space and enabling it to reach Bennu.
In August 2018 Osiris-Rex will complete the
2 million kilometer journey to Bennu
and make its way into a one-kilometer
polar orbit. The spacecraft will need to
slow down to an approach velocity of
just 0.45 miles per hour. Beginning
October 2018 osiris-rex will survey the
asteroid for about a year,
mapping it in total, identifying strange
or unique geological features. It will
use its instruments to create a 3D map
of the asteroid's surface. It will create
a high-resolution global data set
containing color images, altimeter data
and spectrographic data and select an
ideal spot to retrieve a sample. About
2 years after surveying the asteroid,
in July 2020, the spacecraft
will begin to position itself in
preparation for an acquisition of a
sample from the surface of the asteroid.
the spacecraft won't be hitting Bennu
but rather make a maneuver that has been
described as "a safe, smooth, slow
high-five". This "touch and go" maneuvering
will last about 2 months and will be
executed at about point 22 miles per hour
At least two ounces or 60 grams of
asteroid material will be collected. Then
the spacecraft will spring back out into
a safe orbital distance. March 2021
is the month the window for
departing Bennu opens up.
Osiris-Rex will execute a main engine
burn that helps put the spacecraft on a
path towards Earth, with the goal of
making it back to Earth by around
September 2023. During September 2023
Osiris-Rex will jettison the capsule
containing the asteroid sample about
four hours away from atmospheric reentry.
The sample will dive back toward Earth
and land in the Utah desert for NASA to
retrieve and bring back to the Johnson
Space Center in Houston.
Osiris-Rex itself will perform a
deflection maneuver that shoots it back
into a stationary orbit around our Sun
ending its seven-year mission to Bennu
Although developed for science, the
instruments on osiris-rex are similar to
those necessary for an asteroid mining
mission. The success of the Osiris-Rex
mission to Bennu will show us that we
can, in the future go to an asteroid, get
material and bring it back to Earth.