What are asteroids? How much of the stuff
we hear about them is science fiction and how much is science fact? Join the 321science
team as we explore the Solar System’s space rocks.
Asteroids have many different reputations. Science fiction views them as navigation hazards,
colonization frontiers, and threats to the safety of planet Earth.
Are these depictions anywhere close to scientific fact? Or are they just science fiction?
First, what are asteroids? Asteroids are space rocks that range in size from a few meters
up to almost a thousand kilometers in diameter, like Ceres, which is so large that it is also
called a dwarf planet. Most asteroids orbit in the main belt,
a region of the Solar System between the orbits of Mars and Jupiter.
Astronomers have already discovered over five hundred thousand asteroids, and scientists
estimate that the main belt is home to one to two million objects larger than one kilometer.
With so many space rocks flying around, is Although the main belt is full of millions
of asteroids, space is so vast that they actually have lots of room.
In fact, the average distance from one kilometer-sized asteroid to another is thought to be about
three million kilometers. Asteroids aren’t navigation hazards at all;
instead, scientists have to plan spacecraft trajectories very carefully to ensure that
they will successfully encounter asteroid targets. from the formation of the Solar System, the
leftover pieces that Jupiter’s massive gravity prevented from forming into a planet.
The asteroids are all much smaller than planets, and they don’t have enough gravity to hold
an atmosphere nor do they have spinning cores to create magnetic fields.
Without an atmosphere or magnetic field, an asteroid surface is largely unprotected from
the Sun’s heat and other cosmic radiation, making it inhospitable for life.
Asteroids might be large, dead rocks, hard to live on, but they do hold promise as sites
for mining precious metals and other elements. Some might hold hydrogen and oxygen that can
be used for water and fuel needed for exploration and mining.
Scientists and engineers are beginning to make plans to mine asteroids for these resources
to use here on Earth and for outposts in the Solar System.
Are asteroids threatening to Earth? Not always. Long before asteroids seemed threatening,
they brought water and the building blocks of life to early planet Earth. They started
off friendly and helped Earth develop life. But just as they brought materials early on,
rare and large impacts caused mass extinctions, like the event that destroyed the dinosaurs
about 65 million years ago. Even today small asteroids fly by the Earth
quite frequently. Astronomers have discovered over one thousand
potentially hazardous asteroids that might threaten Earth again someday.
Scientists are studying these objects to learn about the threat of asteroid impact,
and what might be done to avoid the fate of the dinosaurs or even smaller but still messy
collisions. The OSIRIS-REx mission is sending a spacecraft
to visit one of these potentially hazardous asteroids named Bennu.
OSIRIS-REx will precisely measure Bennu’s orbit, and the small orbit deviations caused
by sunlight as a result of the Yarkovsky effect, to determine whether Bennu will impact the
Earth in about two hundred years. And while it analyzes the future orbit, OSIRIS-REx
will also map the surface and collect a sample of material that formed the building blocks
of life and return it to Earth to tell us about our origins and how useful asteroids
can be for future exploration. Science fiction? – not this time! Science fact!
You can learn more about OSIRIS-REx and Bennu by clicking on the
links. This video is an OSIRIS-REx production. OSIRIS-REx
is a partnership of the University of Arizona, NASA Goddard Space Flight Center and Lockheed