2 research outputs found
Observations of a very bright fireball and its likely link with comet C/1919 Q2 Metcalf
A very bright fireball called BÂŽejar (SPMN110708), with a maximum brightness of â18, was
observed over much of Spain as well as parts of Portugal and France on 2008 July 11 at
21:17:39 UTC. Fortuitously, it flew over many of the instruments that are part of the Spanish
Meteor and Fireball Network so that accurate measurements of its properties were recorded.
We describe these observations and make deductions from them regarding the nature and
origin of the body that gave rise to this fireball. The bolide first became visible at a height of
98.3 km, attained its maximum brightness at a height of 26 km and finished at a height of 21.5
km. These values are very much in line with other well-known fireballs producing meteorites.
Standard calculations based on the meteoroidsâ ability to survive in the atmosphere suggest
a strength for the remnant that survived to this height of about 14 MPa, similar to those for
meteorite-dropping bolides. So far, this fireball looks typical and one might well expect to find
meteorites on the ground in due course. The heliocentric orbit of the meteoroid determined
from the observations had a perihelion essentially at the Earthâs orbit and an eccentricity
of 0.775, so that the orbit extends far beyond Jupiter, nearly reaching Saturnâs heliocentric
distance and is a typical orbit for a member of the Jupiter family of comets. This is unlike other
bright fireballs, where aphelion is within the asteroidal belt and clearly points to an asteroidal
origin. The orbit is also very similar to the mean orbit of the Omicron Draconid meteor shower,
which is an additional pointer to this fireball being of cometary origin. If the parent was indeed
a comet, this has implications for the internal structure of comets in that significant-sized
non-icy inclusions must exist there. This is not surprising, but this is probably the first time
that direct evidence has been found showing that this is the case. Further, such chunks can only
be released through the catastrophic breakup of the nucleus. Remarkably, a candidate for the
parent of the Omicron Draconid meteor shower is comet C/1919 Q2 (Metcalf) which suffered
a catastrophic breakup in the early decades of the last century