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The Hunt for Asteroids
 
A few NASA-funded astronomer teams are always on the hunt for potentially
hazardous near-Earth objects, asteroids and comets whose orbits periodically
bring them within 30 million miles of Earth's orbit. At NASA, the Planetary
Defense Coordination Office supports the search programs, while also planning
and coordinating any response to possible asteroid impacts.
 
https://www.youtube.com/watch?v=MQi0R6PCROI
 
Lindley Johnson Heads up this NASA office. He says, "We oversee several
NASA-supported search programs that detect and track near-Earth objects," he
explains. "The rate of asteroid discovery has increased considerably due to
these dedicated astronomers and to upgraded telescopes coming online in recent
years."
 
As part of NASA's planetary defense strategy, the Center for Near Earth Object
Studies at the Jet Propulsion Laboratory analyzes the data collected on
near-Earth objects and publishes the running statistics on numbers and types
discovered.
 
Johnson says, "After almost 20 years of searching, over 93% of the near-Earth
objects larger than one kilometer (.62 miles) are already discovered. The focus
is now on finding 90% of those larger than 140 meters (450 feet). Almost 7,700
of these are now being tracked, but we believe there are still over twice that
number out there to be found."
 
NASA is not only hunting asteroids, it's also working on ways to defend Earth
against them. Astrodynamicists at the Center for Near Earth Object Studies
predict orbits a century into the future to determine whether there are any
risks for impact.
 
Johnson says, "Asteroid impacts are predictable and preventable. If we can find
them before they strike, we can precisely predict their paths and time of
possible impact. And we now have the space technologies to divert them."
 
For example, if an approaching asteroid were detected early enough, its path
could be altered by using a large spacecraft as a `gravity tractor.' It would
fly alongside the asteroid for an extended time and slowly pull it out of
Earth's path using nature's virtual tug-rope -- gravity. Another method
involves sending a heavy, high-speed spacecraft into the path of an approaching
object to strike it at the right time and place. This technique, called the
kinetic impactor, could slow or speed up the asteroid into a different
trajectory, away from the Earth's path.
 
And then there's the Hollywood option.
 
"This is a last resort measure," says Johnson.  "It involves exploding a device
close enough to an asteroid that the super-heated surface material blows off,
creating a powerful, rocket-like push. Though quite effective if time is short,
it would take a lot of coordination and approval not only within the U.S.
government, but also with the international community. Another reason we should
find any impactors as early as possible is so more benign methods can be used."
 
All these techniques are in some stage of study or design. Meanwhile, the hunt
for potentially hazardous asteroids goes on.
 
Johnson says, "After all, at NASA every day is an Asteroid Day."
 
For more on objects in and around Earth's neighborhood, visit science.nasa.gov
 
 
Regards,
 
Roger

--- PQUSA