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46th Lunar and Planetary Science Conference (2015)
1291.pdf
Tektite Observations and Suborbital Analysis. T. H. S. Harris1 and H. Povenmire2, 1 Orbit Analyst and Propulsion Engineer retired, Lockheed-Martin (223 Union St. #1 Brooklyn NY 11231, [email protected] 718
344 6016), 2Florida Institute of Technology (7560 Greenboro Dr. #4, Melbourne FL 32904, [email protected]).
Introduction: Tektites offer unique evidence of
detailed impact process mechanics, although tektite
formation mechanisms remain elusive. Tektite forming impacts are most likely very energetic (>20 gigaton
TNT) [1], making them important to understand.
Although the source crater for the largest known
tektite strewn field remains unknown [2], the Australasian (AA) strewn field has expanded to include the
Trans-Antarctic Mountains [3], the S. W. Indian Ocean
[1], Southern China, and possibly two points in N. W.
Canada [2,4] for an area on the order of 1/4 to 1/3 of
Earth’s surface [2], making it the largest known strewn
field. The Central American strewn field source crater
also remains unconfirmed [4]. N. W. Canadian tektites
need further confirmation as AA family, e.g. petrographic, Rb-Sr & Sm-Nd isotopic, etc.
Discussion: Unexplained observations remain in
the field of tektite study. Within the 786 ka AA strewn
field alone such observations include: splash form tektites exhibit very high 10Be levels not accountable from
the bolide or non-aqueous sediment [5] (although
available from a vaporized or ionized ice sheet); the
only known ablated tektites found in the ocean were
within 20 centimeters of the top of the sedimentary
column, one of which had a leeward surface impact
spall from an impact after solidification and cooling
(during free fall before reaching ocean surface?) [6];
layered tektites exhibit a lack of evidence of ablation
[7]; microtektites are found in Antarctica at a range
>10,000 km from the strewn field centroid [3, 8]; water
content and 10Be content show some indication of systematic cross-variation by latitude and indicate a very
wet formative environment [9]; and the estimated AA
tektite mass is currently ~ 10 billion metric tons [1].
A 2.5 to 12 Gt fireball may produce orbital speed
outflow (>7.9 km/s) above an atmospheric scale height
and carry ~10 micron-scale particles to ~700 km altitude [10]. Outflow velocity above orbital velocity
allows global transport. At 10 km/s launch velocity, an
elevation of ~50 at ~285 azimuth puts you at MSN48G (S. tropical fall site) from a mid N latitude launch
~ 180 longitude away, or ~20 elevation at ~63 azimuth,
with the former taking ~ 4 hr and the later taking ~7
hrs. 10 km/s is from australite button flange testing.
AA tektite enigmas include thorough mixing of the
microtektite melt with little or no volatilization [11],
selective volatilization of layered tektites [11, 12], uniform Fe oxidation state throughout the strewn field
although not the case with the N. American impact at
Chesapeake VA, and a substantial lack of detectable
bolide component within splash forms [11]. With
Earth deep in the MIS 20 ice age at the time of the 786
ka AA event, ice sheet surfaces were extended.
The Central European strewn field is associated
with the Ries crater of excavated volume 124-200 km3
[13]. 2.5 g/cm3 density and 162 km3 gives ~ 6.6 x 1013
metric tons of excavated mass for Ries. The Ries tektite mass estimate is ~ 106 metric tons [14], for a
crater-to-tektite mass ratio of ~ 6.6 x 107:1. Applied to
the AA case, this estimate gives an excavated mass of
~ 6.6 x 1017 metric tons or ~ 660 times the mass of
Earth’s atmosphere believed to be ~ 5.1 x 1015 metric
tons [15]. Yet the AA crater remains unfound.
Global atmospheric transient is a dominant guideline for AA tektite transport and trajectory analyses.
Vertical plume outflow velocity at orbital speeds and
Earth rotation during the many hours of such a global
atmospheric transient should clearly yield intercontinental tektite transport.
Recently identified Central American tektites in
Belize and Guatemala are coeval with the AA tektites
within precision of measurement, with different silica
content from the AA family [16]. A layered tektite has
now been identified in that horizon in Belize [16]. Is
there a missing Central American crater?
The Lake Bosumtwi and North American tektite
impacts are examined for their own observations, and a
comprehensive list is generated from the known tektite
strewn fields.
Volatile target overburden, oblique impact, bolide
definition, gas/plasma dynamics and Orbit Analysis are
considered in light of tektite observations. The centroid of a strewn field does not have to coincide with
the crater at all geographically for large impacts, especially those with significant volatile target component.
Historic tektite trajectory analyses are constrained
by ablation-derived flight angle values close to horizontal [17,18] or by a minimum energy assumption as
was common practice in the 1960’s, the era of ICBM
development. Atmospheric entry velocity derived by
tests to recreate flange button flattening of ablated tektites [18] and other constraints are considered in light
of recent hypervelocity impact test findings.
Summary and Conclusion: Automated Orbit
Analysis software helps identify candidate geographic
source crater regions via kinetic imprints which match
46th Lunar and Planetary Science Conference (2015)
specific conditions of directional hypervelocity impact
test results for some azimuth.
Candidate crater regions must then be examined
closely for gravimetric and magnetic anomalies, shock
metamorphism, meteoritic component and associated
gradient, and other impact signatures within the geologic record [19] consistent with tektite observations,
the hypervelocity test scenario and target definition.
References: [1] B. P Glass (1982) GSA Special
Paper 190, 251-256. [2] Kenkmann et al. (2004) 77th
Meteoritical Soc. Mtg., pdf 5322 [3] L. Folco et al.
(2007) Geology v. 36 no. 4, 291-294. [4] H. Povenmire
(2012) 75th Meteoritical Society Mtg., 5016. [5] D. K.
Pal et al. (2002) Science vol. 218 [6] B. P. Glass & D.
R. Chapman (1995) LPS XXVI Abstracts, 467-468. [7]
B. P. Glass, personal communication. [8] B. P. Glass
1291.pdf
and C. Koeberl (2006) Meteoritics and Planetary Sci.
41 no. 2, 305-326. [9] Watt et al. (2011) Meteoritics
and Planetary Sci. 1-8. [10] E. M. Jones and J. W.
Kodis (1982) GSA Special Paper 190, 175-186. [11] C.
Koeberl (1994) GSA Special Paper 293, 133-147. [12]
G. S. Ridenour (1986) Meteoritics, Vol. 21 No. 3. [13]
R. Grieve (1982) GSA Special Paper 190, 25-37. [14]
M. Trnka & S. Houzar (2002) Bulletin of Czech. Geo
Survey no. 4, 283-302. [15] F. Verniani (1966) Journal of Geophysical Research, vol 71 issue 2, 385–391.
[16] Hal Povenmire, personal communication. [17] J.
S. O’Keefe III et al. (1973), Journal of Geophysical
Research, v. 78 no. 17, 3491-3496. [18] D. R. Chapman (1964) Geochemical Et Cosmochimica Acta N6431571. [19] M. Davias (2010) Geo. Society of America
ann.
mtg.
116-13.
Strewn Kinetic Profile: Normalized to Earth escape KE, a solution family is defined by strewn field and (proposed) astrobleme location or region. Example hypervelocity impact test trend identified within, lower right pane.