Wednesday, 4 July 2018

OT: the bright fireball of 29 June 2018, 21:30:14 UT

image (c) Felix Bettonvil, Utrecht. Click to enlarge

Barely two weeks after an earlier brilliant twilight fireball discussed in a previous post appeared over the Netherlands, another bright fireball was observed, again in bright evening twilight. This fireball of about magnitude -6 occurred on 29 June 2018 at  21:30:14 UT (23:30:14 local time). It had a duration of over 3.6 seconds.

The fireball was photographically well covered this time, as it was captured by six all-sky meteor cameras (Borne, Bussloo, Dwingeloo, Ermelo, Utrecht and Wilderen) plus by an amateur astronomer from Kerkrade who was making a time lapse of the night sky. The image above (courtesy of Felix Bettonvil)  shows the fireball as it appeared over the camera station in Utrecht. Almost literally right over it: the lateral distance between the camera position and the nominal ground projected meteor trajectory is only 185 meters!

As several stations were equipped with an electronic or rotating shutter in front of the lens (see the interuptions in the trail in the image above, at 10 breaks/second), there is speed information for this fireball as well. In fact, it delivered a very fine deceleration curve (data from stations Borne, Utrecht and Dwingeloo), showing how the meteoroid rapidly slowed down upon entry into the atmosphere due to friction with the atmosphere:

click diagram to enlarge

click to enlarge
The fireball entered from the south-southeast with a  speed of 21.5 km/s and under a low 27 degree entry angle. It first became visible at 80 km altitude over the Betuwe area near 5.416 E, 51.822 N. It ended at 43 km altitude over the western suburbs of Amsterdam, near 4.837 E, 52.360 N, with an end speed of 9 km/s. End altitude and end speed point out that nothing was left at that point: there are no meteorites on the ground.

click to enlarge
The radiant of the fireball is located in Scutum: the geocentric radiant is at RA 276.4, DEC -11.4, with a  geocentric velocity of 18.2 km/s. The resulting orbit is an Apollo orbit with an orbital inclination of 7 degrees, an orbital period of 2.15 years and aphelion at 2.7 AU. The object was hence of asteroidal origin: a very small piece of asteroid.

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Acknowledgement: I thank Mark-Jaap ten Hove, Johan Pieper, Koen Miskotte, Jean-Marie Biets, Felix Bettonvil and Peter van Leuteren for making their imagery available for analysis.