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

(meteorobs) [IMO-News] On the terrestrial nature of ice objects


------- Forwarded Message

From: =?iso-8859-1?Q?Josep_M=AA_Trigo_i_Rodriguez?= <jmtrigo@ctv.es>
To: "'IMO-News mailing list'" <imo-news@imodot net>,
        "'Juli Castellano i Roig (SOMYCE)'" <julioc@comfiadot net>
Cc: "'Douglas O.ReVelle'" <dor@vega.lanldot gov>,
        =?iso-8859-1?Q?=22=27Jor?= =?iso-8859-1?Q?di_Llorca_Piqu=E9_=28U=2EB=29=
27=22?= <jllorca@kripto.qui.ub.es>
Date: Wed, 26 Jan 2000 17:37:38 +0100
Subject: [IMO-News] On the terrestrial nature of ice objects

ON THE TERRESTRIAL NATURE OF ICE OBJECTS

The Spanish Fireball Network is an interdisciplinary project of three =
mediterranian universities (Valencia, Castello and Barcelona) together =
with the Research Catalan Foundation (FCR). We analyse the fireballs =
produced by the entry of meteoroids in the Earth atmosphere using =
photographic and video techniques. We explain below our mean arguments =
to claim that these ice ball objects cannot have cosmic origin.=20

- - Actually our knowledge on the composition of these ice balls is =
increasing. Past week the Chemistry Department of the University of =
Valencia obtained a detailed analysis of one reliable ice ball fallen =
near Valencia. From this and other analysis obtained by the Spanish =
Higher Council for Scientific Research (CSIC) we can say that the =
objects really fallen from the sky are composed by water ice with little =
quantities of some common salts. In all cases the isotopic composition =
corresponds closely to the natural isotopic mix of atmospheric water. In =
these conditions, we must remark here that none of solar system objects =
(comets either) have similar composition. Comets are bodies formed by =
ice-dust dark aggregates as suggested long time ago Fred L. Whipple. We =
know that cometary ice is a very complex mixture of dust particles with =
ices of water, methane, ammonia, etc...In any case all cometary =
components have important isotopic anomalies.

- - Velocities of Solar System objects at their encounter with the Earth =
atmosphere are necessary within a limit, consequence of encounter =
geometry and the relative velocity between the bodies. The lower impact =
velocity of a meteoroid with our atmosphere is 11,2 km/s (considering =
only Earth's gravity). The upper limit is close to 73 km/s (considering =
a 30.3 km/s velocity plus a 42.5 km/s velocity to an object following a =
parabolic orbit). During the entry the preheating is intense and the =
surface temperature of meteoroid rises rapidly. Surface temperatures as =
low as 500 K and shock pressures can disrupt with rapidity a homogeneous =
ice body.=20

- - The mass loss during the atmospheric ablation can reach the 100% =
meteoroid mass, especially in low-density bodies as reported. In any =
case them must originate an impressive fireball seen by a lot of people. =
No one reports such event connected to the ice-ball falls. Our =
Photographic Network either reports a significative fireball activity =
increase during the past month.

- - As consequence of high velocity entry and hard atmospheric ablation =
the fall of a 5kg-ice body in the Earth surface implies a huge entering =
body. But we cannot explain either the fall of a single 5 kg object. The =
reason is that to low density material (as water ice) is expected the =
disintegration in multitude of fragments, falling in an impressive rain =
as has been reported in real meteorite events.

	- Finally we can calculate the impact expected velocity into the Earth =
surface of 1-10kg mass bodies. Assuming free fall after deceleration =
this velocity would be close to 100 m/s. We think clearly that such =
velocity is higher that the estimated in the majority of reported fall =
events.

All previous arguments leads to conclude that the reported falls of ice =
objects in Spain and, recently, in Italy are originated by an =
atmospheric unknown phenomenon or, more probably as in other occasions, =
due to natural ice formation on the fuselage or ejection of on-board =
water in aeroplanes. In any case a cosmic origin is highly improbable.=20
*******************************************************************
Josep Ma. Trigo i Rodriguez=20
SPANISH PHOTOGRAPHIC METEOR NETWORK (SPMN)
Dept. Astronomy & Astrophysics, Universitat de Val=E8ncia
Prof. Dept. Experimental Sciences, Universitat Jaume I
E-mails: jmtrigo@ctv.es / trigo@exp.uji.es
Web page: http://www.ctv.es/USERS/jmtrigo/
Phones: (+Spain Code 34)  964 -  282584  / 282968  (office)=20
(964) 395064 (part.) Fax: 964 - 285161
Postal address: c/ Manuel de Falla 26,=20
12.560 Benicassim (Castello) SPAIN
*******************************************************************=20

------- End of Forwarded Message


To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html