[meteorite-list] Additional Details on the Large Fireball Event over Russia on Feb 15, 2013

From: James Beauchamp <falcon99_at_meteoritecentral.com>
Date: Fri, 1 Mar 2013 19:40:38 -0600
Message-ID: <6E187527-2593-4AB1-8DB6-52DBB7C493A4_at_sbcglobal.net>

It is not heated by friction!

Sent from my iPad

On Mar 1, 2013, at 5:47 PM, Ron Baalke <baalke at zagami.jpl.nasa.gov> wrote:

>
> http://neo.jpl.nasa.gov/news/fireball_130301.html
>
> Additional Details on the Large Fireball Event over Russia on Feb. 15, 2013
> Don Yeomans & Paul Chodas
> NASA/JPL Near-Earth Object Program Office
> March 1, 2013
>
> The large fireball (technically, a "superbolide") observed on the
> morning of February 15, 2013 in the skies near Chelyabinsk, Russia, was
> caused by a relatively small asteroid approximately 17 to 20 meters in
> size, entering the Earth's atmosphere at high speed and a shallow angle.
> In doing so it released a tremendous amount of energy, fragmented at
> high altitude, and produced a shower of pieces of various sizes that
> fell to the ground as meteorites. The fireball was observed not only by
> video cameras and low frequency infrasound detectors, but also by U.S.
> Government sensors. As a result, the details of the impact have become
> clearer. There is no connection between the Russian fireball event and
> the close approach of asteroid 2012 DA14, which occurred just over 16
> hours later.
>
> New Fireball Data
>
> U.S. Government sensor data on fireballs are now reported on the NASA
> Near-Earth Object Program Office website at
>
> http://neo.jpl.nasa.gov/fireballs
>
> The February 15th event is the first entry on this new site, and it
> provides the following information about the fireball:
>
> * Date and time of maximum brightness: 15 Feb. 2013/03:20:33 GMT
> * Geographic location of maximum brightness:
> Latitude: 54.8 deg. N
> Longitude: 61.1 deg. E
> * Altitude of maximum brightness: 23.3 km (14.5 miles)
> * Velocity at peak brightness: 18.6 km/s (11.6 miles/s)
> * Approximate total radiated energy of fireball: 3.75 x 10^14
> Joules. This is the equivalent of about 90 kilotons (kt) of TNT
> explosives, but it does not represent the total impact energy (see
> note below).
> * Approximate total impact energy of the fireball in kilotons of TNT
> explosives (the energy parameter usually quoted for a fireball):
> 440 kt.
>
> Note that the total energy of a fireball event is several times larger
> than the observed total radiated energy. The JPL fireballs website uses
> the following empirical formula derived by Peter Brown and colleagues to
> convert the optical radiant energy Eo into an estimate of the total
> impact energy E (see: Brown et al., The flux of small near-Earth objects
> colliding with the Earth. Nature, vol. 420, 21 Nov. 2002, pp. 294-296):.
>
> E = 8.2508 x E_o ^0.885
>
> During the atmospheric entry phase, an impacting object is both slowed
> and heated by atmospheric friction. In front of it, a bow shock develops
> where atmospheric gases are compressed and heated. Some of this energy
> is radiated to the object causing it to ablate, and in most cases, to
> break apart. Fragmentation increases the amount of atmosphere
> intercepted and so enhances ablation and atmospheric braking. The object
> catastrophically disrupts when the force from the unequal pressures on
> the front and back sides exceeds its tensile strength.
>
> This was an extraordinarily large fireball, the most energetic impact
> event recognized since the 1908 Tunguska blast in Russian Siberia.
>
> The meteorites recovered from the Chelyabinsk fireball are reported to
> be ordinary chondrites, which have a typical density of about 3.6 g/cm^3.
> Given the total energy of about 440 kt, the approximate effective
> diameter of the asteroid would be about 18 meters, and its mass would be
> roughly 11,000 tons. Note that these estimates of total energy, diameter
> and mass are very approximate.
>
> Where Did the Chelyabinsk Impactor Come From?
>
> An approximate path for the Chelyabinsk impactor can be calculated from
> the newly released fireball data. (A similar calculation can be made
> from analysis of video records of the event; both methods yield similar
> results.) The first diagram shows the ground track of the impactor over
> the last minute or so before impact. The altitudes along this ground
> track have been called out and the asterisk on the path indicates the
> point of peak brightness, just south of Chelyabinsk.
>
> [Diagram 1: Ground track of impactor showing altitude values along the track]
>
> The second diagram shows the impactor's final trajectory over the last
> several hours, as it approached the Earth along a direction that
> remained within 15 degrees of the direction of the Sun. Asteroid
> detection telescopes cannot scan regions of the sky this close to the Sun.
>
> [Diagram 2: Approximate final trajectory of impactor]
>
> The third diagram shows the orbit of the impactor about the Sun. The
> orbit reaches from the asteroid belt at its farthest from the Sun to
> near the orbit of Venus at its closest to the Sun. The impactor had
> likely been following this orbit for many thousands of years, crossing
> the Earth's orbit every time on its outbound leg.
>
> [Diagram 3: Heliocentric orbit of asteroid that impacted near Chelyabinsk
> Russia]
>
> Was the Chelyabinsk Fireball Related to the Close Approach of Asteroid
> 2012 DA14?
>
> Asteroid 2012 DA14 made a very close flyby of the Earth just over 16
> hours after the Russian fireball event, passing within 27,700 km (17,200
> miles) of the Earth's surface, but there is no connection whatever
> between these two events. First of all, the two objects approached the
> Earth from completely different directions, and had entirely different
> orbits about the Sun. A custom version of the JPL orbit display applet
> has been created to show the orbits of the Chelyabinsk impactor and 2012
> DA14 at the same time:
>
> http://neo.jpl.nasa.gov/orbits/2012da14.html
>
> A second reason we know the two asteroids approaching Earth on Feb. 15
> were unrelated is their disparate compositions. Telescopic spectral data
> do not support any physical connection between asteroid 2012 DA14 and
> Chelyabinsk meteorites. Nicholas Moskovitz and Richard Binzel (MIT)
> report 2012 DA14 displays spectral colors which suggest a carbon
> dominated composition similar to CO or CV carbonaceous chondrite
> meteorites with abundant calcium- and aluminum-rich inclusions. On the
> other hand, meteorite fragments being recovered from the fireball event
> are reported as silicate-rich ordinary chondrites; a completely
> different and unrelated class of meteorites. About 80% of all meteorite
> falls are in the ordinary chondrite category.
>
> Acknowledgements
>
> Peter Brown, University of Western Ontario and William Cooke at the
> Marshall Space Flight Center provided impactor details. Paul Chodas and
> Steve Chesley (JPL) provided orbital computations and diagrams.
> Ron Baalke (JPL) provided the custom interactive applet showing the
> heliocentric orbits of both 2012 DA14 and the asteroid impacting the
> atmosphere over Russia. Richard Binzel (MIT) provided information on the
> nature of the atmospheric impactor and near-Earth asteroid 2012 DA14.
>
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Received on Fri 01 Mar 2013 08:40:38 PM PST