Monday 13 February 2017

Looking for pieces of the Piecki Meteor.

On 12 September 2016 a bright fireball meteor (meteor that shines brighter than the planet Venus). This was tracked by six stations of the Polish Fireball Network, which was set up in 2004 to track such meteors over Poland, part of the European Fireball Network, which was set up in the mid twentieth century to study such events.

In a paper published on the arXiv database at Cornell University Library on 30 January 2017, Arkadiusz Olech of the Nicolaus Copernicus Astronomical Center, Przemysław Żołądek of the Comets and Meteors Workshop of the Polish Fireball Network, Zbigniew Tymiński of the Narodowe Centrum Badań Jądrowych, and Marcin Stolarz, Mariusz Wiśniewski, Marcin Bęben, Thomas Lewandowski, Krzysztof Polak, Ashish Raj and Paweł Zaręba, all of the Comets and Meteors Workshop of the Polish Fireball Network, describe the results of a study based upon the data collected on the Piecki Meteor by the Polish Fireball Network.

The fireball was observed by six observation stations, Jeziórko, Rzeszów, Stary Sielc, Łódź, Koźmin Wielkopolski and Brwinów, though data from two of these was discarded and not included in the study, Łódź because of poor data quality and Rzeszów because it was directly in the path of the meteor. The remaining stations were used to calculate the trajectory of the meteor over a 91 km path from south to north, during which it descended from a height of 91.1 km to 26.0 km over a period of 6.5 seconds.

The video image of PF120916 Piecki fireball captured in Stary Sielc station (PFN52). Żołądek et al. (2017).

The object entered the atmosphere at a speed of 16.7 kilometres per second, and began decelerating due to friction with the Earth's atmosphere after about three seconds. The meteor had an initial brightness of -1.3 (Venus at its brightest has a brightness of -4.5, while objects with values above 0 are essentially invisible to the naked eye), and reached -9.0 after about two seconds, which was sustained for about three seconds followed by a flare to about -9.2, then the object dimmed to about -4.5 before vanishing.

The luminous trajectory of the PF120916 Piecki fireball over Poland and the location of the PFN stations which recorded the phenomenon. Żołądek et al. (2017).

The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Żołądek et al. were able to calculate potential trajectories for hypothetical dark objects derived from the Piecki Meteor using data from weather balloons launched from Kaliningrad and Łeba that evening.

The dark flight tracks for 2−15 kg meteorites. Different colors of the tracks are used to distinguish the atmosphere profiles from Kaliningrad and Łeba. Żołądek et al. (2017).

Using this data Żołądek et al.identified an area 4 km long and 100-200 m wide, roughly 4 km to the south of Rzeszów as the most likely area to find any fragments that fell to the ground. This area was visited by teems of volunteers several times in September, October and November 2016, but no fragments were recovered; however the searched were hampered by poor weather and a low number of volunteers, and the search area included both freshly ploughed fields and an area of lush swampland, so this was unsurprising. An additional visit, is being planned for the spring.

The computed impact area of Reszel meteorite caused by PF120916 Piecki fireball. The impact points for 15, 5 and 2 kg meteorites and trajectory axis are also shown. The area searched by our expeditions is marked by tilted stripes. Żołądek et al. (2017).

The data collected from the stations was also used to trace the trajectory backwards, to determine the orbit of the original object before it struck the Earth. This was found to be close to those of a number of Near Earth Asteroids, all of which were Apollo Group Asteroids (asteroids that are on average further from the Sun than the Earth, but which d get closer) on Earth-crossing orbits, and some of which were Potentially Hazardous Objects (asteroids possibly larger than 150 m in diameter that occasionally come within 0.05 AU of the Earth). Interestingly one of these objects, 2014 SH224, made close approach to the Earth only six days after the Piecki Fireball, suggesting the objects may have been related.

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