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Forwarded From Josep Ma. Trigo i Rodriguez (jmtrigo@ctv.es)

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.

- 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.

- 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 lead to the conclusion 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.

Josep Ma. Trigo i Rodriguez
SPANISH PHOTOGRAPHIC METEOR NETWORK (SPMN)
Dept. Astronomy & Astrophysics, Universitat de Valencia              

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