[meteorite-list] Physicist's Journey Reveals Smaller Asteroids Could Cause Bigger Problems

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 20 Nov 2013 13:02:21 -0800 (PST)
Message-ID: <201311202102.rAKL2L19010088_at_zagami.jpl.nasa.gov>

https://share.sandia.gov/news/resources/news_releases/boslough_asteriod/

Physicist's journey reveals smaller asteroids could cause bigger problems
Sandia Labs News Release
November 20, 2013
 
ALBUQUERQUE, N.M. - Once in a lifetime, a physicist may get a chance to
test his theories and simulations in a real-life event that changes the
course of his scientific life. But rarely does that opportunity literally
fall from the sky.

That's the impact of the Feb. 15 asteroid that burst over the Russian
city of Chelyabinsk on Sandia physicist Mark Boslough, subject of a TV
documentary that airs tonight and co-author of a recent cover story in
Nature about the asteroid fireball that injured about 1,500 people and
damaged more than 7,000 buildings, collapsing roofs and breaking thousands
of windows.

Boslough's journey to Russia shortly after the impact is chronicled in
the NOVA episode "Asteroid; Doomsday or Payday," which will air on Public
Broadcasting Service stations beginning today.

The show focuses on the destructive potential of asteroids, chronicling
how Boslough and his colleagues learn that small asteroids can do far
more damage than previously thought. The Nature paper also suggests that
there may be more small asteroids than formerly thought.

The day the asteroid hit, Boslough learned of the event via Facebook from
posts of Russian news stories and YouTube videos showing an object that
exploded in the Russian sky.

"I saw it on Facebook long before the sound wave had even arrived in this
part of the world," Boslough said, estimating the transglobal sound wave
took more than seven hours to reach New Mexico. "I really didn't expect
to experience this in my lifetime."

As one of the first scientists to visit Chelyabinsk after the asteroid
struck, Boslough set out to discover where the object came from. Because
it came down near a populated area, he and his colleagues were able to
collect videos from people who caught the asteroid on film and video,
especially the ubiquitous Russian dashboard cameras, a staple in establishing
blame in traffic mishaps.

"This event was certainly one of the best-documented asteroid events ever,"
said Boslough.

Boslough's goal was to perform stellar calculations of the asteroid's
trajectory by visiting - at night when the stars shone - the exact spots
where the footage was recorded.

"If the stars show up on the digital camera, we can get those angles and
then calibrate that image that was taken from the dash cam, and know exactly
the angles to the trajectory of the fireball," he said in the documentary.
"We'll have a very precise trajectory as it streaked through the atmosphere,
so we can backtrack that to get the orbit, the pre-impact orbit."

The program also discusses how asteroids can contain rare and valuable
elements, leading researchers to seriously evaluate the benefit of harvesting
them for their rare elements.

But Boslough also wants the research community to pay more attention to
the potential risk that asteroids present.

"If something like the Tunguska event of 1908 happened now, it could kill
hundreds of thousands or even a million people, if it happened right over
a big city," he said in the documentary. "An asteroid has more damage
potential on the ground than a nuclear bomb of the same energy."

Boslough was part of a team of 33 researchers who completed the study
featured in Nature. "A 500-kiloton airburst over Chelyabinsk and an enhanced
hazard from small impactors" examines the characteristics of the fireball.
Boslough and his colleagues also used the simulations to help design the
journal's cover.

You also can see an animated simulation of the airburst produced by Boslough,
as well as scientific animations and images by Sandia contractor and visual
effect expert Brad Carvey and visual effect expert Andrea Carvey. Sandia's
Laboratory Directed Research & Development program funded the simulations.

Using data collected from his visit shortly after the asteroid struck,
along with data from an international team, Boslough developed several
additional simulations that he and other researchers have used to model
the explosion and estimate the force of the blast.

The paper's authors performed a global survey of airbursts of a kiloton
or more and found that the number of building-sized objects may be 10
times greater than estimates based on other methods.

The authors, led by Peter Brown of the University of Western Ontario,
estimated the Chelyabinsk event was equivalent to an explosion of about
500 kilotons of TNT. At its peak, the airburst appeared to be 30 times
brighter than the sun.

"Because the frequency of a strike of an asteroid of this size has exceeded
expectations, with three such strikes in just over a century (Chelyabinsk,
Tunguska and a large airburst in the South Atlantic in 1963 detected by
infrasound), the number of similar-sized asteroids capable of causing
damage may be greater than suspected,' Boslough said.

Dick Spalding of Sandia's Nonproliferation Technologies Research and Development
Department also co-authored the paper.

The authors also showed that previous models for estimating airburst damage
do not match the observations.

An earlier paper by Boslough highlights the conclusion that most airbursts
are more damaging than previously thought.

"We really have to rethink the risk from airbursts. Chelyabinsk was unusual
due to the a low inclination at which it entered the atmosphere, but 90
percent of objects enter the atmosphere at a steeper angle and cause more
damage on the surface," Boslough said. That paper, which he wrote two
years ago, was recently published online in Acta Astronautica.

The Chelyabinsk fireball is something those who saw it will never forget,
and neither will Boslough.

"What's amazing to me though, when you think about it, this is part of
an asteroid that had been, floating through space, orbiting the sun for
billions of years" he said for the documentary in a late February interview.
"And two weeks ago, it exploded in the atmosphere, dropped to the ground,
and here I am holding it in my hand! That's amazing."

Sandia National Laboratories is a multi-program laboratory operated by
Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp.,
for the U.S. Department of Energy's National Nuclear Security Administration.
With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia
has major R&D responsibilities in national security, energy and environmental
technologies and economic competitiveness.

Sandia news media contact: Stephanie Holinka, slholin at sandia.gov, (505)
284-9227
Received on Wed 20 Nov 2013 04:02:21 PM PST