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New Year's Asteroid Strike --
presented by Science@NASA
In 2014, the New Year began with a bang -
on the order of about 500 tons of TNT.
That's how much energy asteroid 2014 AA
is estimated to have delivered to Earth's atmosphere
when it exploded over the Atlantic Ocean
on January 1st
at approximately 11:10 pm Eastern Standard Time.
2014 AA was the first asteroid discovered in 2014.
Astronomers of the Catalina Sky Survey
found it during the early hours of January 1st
using one of their telescopes near Tucson Arizona.
Our encounter with this space rock the size of a small compact car
didn't last long, however -
it was only 21 hours
before it crashed into Earth's atmosphere.
'No damage was done,'
says Don Yeomans of the Near-Earth Object Program
at NASA's Jet Propulsion Laboratory.
'It disintegrated harmlessly high above Earth's surface.'
Asteroids the size of 2014 AA
hit Earth several times a year,
so there's nothing remarkable about such an impact.
What's interesting is that it was seen before the impact.
This is only the second time
that astronomers have detected an Earth-impacting asteroid
before it hit.
The first time was back in October 2008
when another small asteroid, 2008 TC3,
hit Earth's atmosphere
and broke-up over northern Sudan.
As many as 600 small meteorites
were recovered from the Nubian Desert after that crash.
Fresh meteorites,
especially those that are associated with a known fall,
are scientifically precious.
The treasure was made even more valuable
because Richard Kowalski at the Catalina Sky Survey
had discovered the asteroid about 19 hours before impact.
Astronomers then had time to observe the object
while still in space
so that researchers could compare what telescopes observed
with the material that was later recovered on the ground.
At first, 2014 AA seemed to be a case of déjà vu -
a two to three meter asteroid discovered by Catalina
almost a full day before impact.
But in this case the asteroid would impact over open ocean
where no meteorites could be recovered.
The impact location was later pinpointed
using data from a network of infrasound sensors
operated by the Comprehensive Nuclear Test Ban Treaty Organization.
While this global network of detectors
was originally intended to monitor for nuclear explosions
that may violate the treaty,
it can also be utilized to pinpoint airbursts
from entering meteors.
Infrasound is a type of very low-frequency sound wave
that only elephants and a few other animals can hear.
Meteors penetrating through Earth's atmosphere
cause ripples of infrasound
to spread through the air of our planet.
By analyzing infrasound records,
it is possible to approximate where a meteor exploded
and how much energy it unleashed.
Weak infrasound signals showed 2014 AA
probably disintegrated over the Atlantic Ocean east of Venezuela -
in good agreement with a ground track
calculated by Steve Chesley
of JPL using the observations taken when it was discovered.
'I estimate that some 10% of the asteroid's mass
could have reached Earth's surface
in the form of ponderable-sized meteorites,'
says University of Western Ontario
physics professor Peter Brown,
who analyzed the infrasound.
'There is a good chance of a meteorite-strew field -
albeit in the middle of the ocean.'
Detecting asteroids before they strike is rare.
However, Yeomans thinks it will become more commonplace in the future.
'There are more than a billion
near-Earth objects in the few-meter size range,' he says.
'As discovery surveys continue to improve,
we will detect more of them before they hit Earth.'
Early detection is, of course,
the objective of NASA's Near-Earth Object Program's
search for hazardous asteroids.
2014 AA is an example of what can be done
with sufficient vigilance.
For more on the detection of near Earth objects,
visit science.nasa.gov