[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

The Taurids - Encke's Comet and Tunguska

GeoZay@aol.com schrieb:

> Every year around this time, folks all over the world find
> themselves in a frenzy over Taurid fireballs. Not surprising
> since their population index is at 2.3....which means most of
> their members are quite bright. Its an old stream with most of
> the smaller particles long removed from the solar wind and other
> processes. The South Taurids have a long peak centering on November
> 5th. The North Taurids also have a long peak, but centering around
> November 12th. To the best of my knowledge, despite of all the
> annual bright Taurid fireballs, none have produced any recoverable
> meteorites. Their combined periods of activity is from roughly
> October 1 thru November 25th. So, expect more excitement from them
> in the next couple weeks and enjoy them while you can. By the way,
> last year while watching the Leonid fireball shower, I recorded a
> -12 North Taurid that sneaked in amongst them. - GeoZay


Hello Geo and List!

Sky and Telescope, December 1978, pp. 497-498:

The Tunguska Event and Encke's Comet

Just what was it that collided with the earth on June 30, 1908, in
central Siberia? A dazzlingly bright daytime fireball was seen, and over
the site of its fall flames and a cloud of smoke appeared. Deafening
explosions were heard at distances up to 1,000 km and were recorded on
seismographs and barographs. To quote Lubor Kresak of the Slovak Academy
of Sciences:
"Hundreds of articles written on the unique Tunguska event of June 30,
1908, offer a variety of competitive explanations. Apart from the
obvious fictions and speculations lacking [in] scientific objectivity
(alien spacecraft, nuclear explosion, antimatter, black hole), every
known type of interplanetary body crossing the orbit of the Earth has
been suggested as the impacting object. The candidates include a small
asteroid - or unusually large meteorite - ranging in composition from
meteoric iron (Yavnel', 1957), to pre-type I carbonaceous chondrite
(F.L. Whipple, 1967), and a small comet, extinct or active, with a dust
tail (F.J.W. Whipple, 1930; Fesenkov, 1961 and 1966)."
Writing in the Bulletin of the Astronomical Institutes of
Czechoslovakia, Dr. Kresak presents strong grounds for surmising that
the Tunguska object was in fact a fragment of Comet Encke, separated
from it thousands of years ago. He begins by noting that although the
impact energy seems to have been comparable to that expended in forming
Arizona's Meteor Crater, no sizable crater was formed in the heavily
damaged Tunguska area. This point favors a low-density impacting body.
The only direct evidence concerning the orbit of the object before it
entered the atmosphere is the position of its apparent radiant in the
sky. The radiant was only about 20° from the direction of the earth's
orbital motion. Thus the event was either a head-on collision of the
earth with an object in retrograde motion (such as a long-period comet)
or an object near the aphelion point of a direct orbit (Apollo-type
asteroid or daylight meteor stream).
The  B e t a  T a u r i d  meteor shower, which peaks at just the right
time of year, has a radiant only 10° from the Tunguska ohject's radiant,
well within the uncertainty of the latter. This Beta Taurid shower is
produced by the meteor stream associated with Comet Encke.
As Dr. Kresak remarks: "The orbit of Comet Encke can be brought into
intersection with the Earth's orbit at the point of the Tunguska event
by a mere rotation of the nodal line from longitude 334° to longitude
278°. In respect [to] the low inclination and differential secular
perturbations, this change appears plausible ... The distance from the
point of the Tunguska encounter to the orbit of Comet Encke, 0.18
astronomical unit, is not excessive, since the nighttime Taurids are
annually observed up to distances twice as large. Remembering that the
radiant position of the Tunguska object is uncertain to at least 10°,
the agreement is essentially perfect. "
According to a 1975 analysis by the Soviet astronomer V.A. Bronshten,
the initial mass of the object was 10^8 to 10^9 kilograms, and it
exploded at a height of five to seven km. Assuming tentatively a density
equal to that of ice, Kresak calculates the initial diameter as 100
meters for this body, which was completely destroyed in 10 seconds
before reaching the ground.
There are several reasons why this object was probably not an active
comet nucleus, but the extinct remnant of one. Statistics of observed
comets seem to indicate that there are no active objects with nuclear
diameters as small as 100 meters. Furthermore, as the diagram of the
intersecting paths of the earth and Tunguska object shows, for several
weeks before the encounter on June 30, 1908, the object was favorably
placed in the evening sky more than 20° from the sun. If an active
comet, it might well have been discovered, but as an extinct one it
would have gone undetected.
"The identification of the Tunguska object as an extinct cometary
fragment appears to be the only plausible explanation of the event; and
a common origin with Comet Encke appears very probable," is Dr. Kresak's
conclusion. He notes that a possible connection with this comet had
previously been suggested in 1969 by I.T. Zotkin.

D.J. Asher, D.I. Steel: On the possible relation between the Tunguska 
bolide and comet Encke. PLANETARY AND SPACE SCIENCE, 1998, Vol.46,  No.
2-3, pp. 205-211:

Almost 2decades ago L. Kresak (Bull. Astron. Inst. Czechoslov. 29,
129-134, 1978) suggested that the Tunguska bolide might be a fragment
of comet Encke, a hypothesis that Z. Sekanina criticized in a 
publication a few years later (Astron. J. 88, 1382-1414, 1983).

... By applying appropriate secular perturbation theory and numerical
integration techniques, it is shown that the necessary dispersion can
be attained within 10 kyr if the semimajor axes of the orbits differ by
similar to 0.05 AU, an amount easily achieved even under the presently
observed non-gravitational forces of 2P/Encke.

Orbital elements for Comet Encke:

Perihelion distance           q = 0.330 890 AU
Eccentricity                       e = 0.850 220
Period                               p = 3.28 years
Argument of perihelion     w = 186. 2443°
Longitude of ascending node = 334.0416°
Inclination                           i = 11.9391°


Best wishes,

Bernd

----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------
References: