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24 April 2003

--Abstract Published in Meteoritics and Planetary Sciences 
(MAPS) 37(7), supplement, p.A122, 2002.

A SMALL IMPACT EVENT ON MARS IN 1951
M.C.L.Rocca
Mendoza 2779-16A,
Ciudad de Buenos Aires,
Argentina (1428DKU), maxrocca{at}hotmail.com

Introduction: Any meteoroid impacting into the thin atmosphere of
Mars penetrates deeper than into the denser Earth atmosphere. As a
rule, meteoroids bigger than 1 meter in size hit the martian surface.
Objects with the size of about 0.1 - 1.0 meters explode high in the
martian atmosphere creating intense blast waves and light flashes. 
Those superbolide events have a luminous efficiency higher than at
the Earth [1], [2]. As part of a search in old scientific
publications one superbolide-impact event on Mars has come to light.
It was reported by the japanese astronomer Tsuneo Saheki, at Osaka
Planetarium. He used a 8-inch reflector, at 400x. The event occurred
on December 8, 1951. 

"At 21:00 I saw a sharp , bright, glaring spot suddenly appear on
Tithonius Lacus. It was as brillant as a 6 th. magnitude star -
decidedly brighter than the north polar cap - and shone with
scintillation for about five minutes. Fadding rapidly, by 21:05 it
looked like a whitish cloudlet, as large as Tithonius Lacus. At 21:10
it was barely visible as a very faint and large white spot, and by
21:40 this part of the martian surface had returned to its normal
state" [3]. 

The four drawings he published are very interesting. The first shows
a radiate structure wich may be explained as ballistic ejecta from
the impact site. Careful searches in old journals may offer puzzling
new examples of superbolide and impact events on Mars.

References:
[1] Kosarev I.B. et al. (2000): MAPS 35 , supplement, pp. A91.
[2] Adolfsson L.G., Gustafson B.A.S. and Murray C.D. (1996): Icarus
    119, pp.144 -152.
[3] Saheki T. (1955) Sky & Telescope 14, pp. 144 -146.

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