Discovery of a new branch of the Taurid meteoroid stream as a real source of potentially hazardous bodies

Taurid meteor shower produces prolonged but usually low activity every October and November. In some years, however, the activity is significantly enhanced. Previous studies based on long-term activity statistics concluded that the enhancement is caused by a swarm of meteoroids locked in 7: 2 resonance with Jupiter. Here we present precise data on 144 Taurid fireballs observed by new digital cameras of the European Fireball Network in the enhanced activity year 2015. Orbits of 113 fireballs show common characteristics and form together a well defined orbital structure, which we call new branch and which was evidently responsible for the enhanced activity. This new branch is part of Southern Taurids and was encountered by the Earth between October 25 and November 17. We found that this branch is characterized by longitudes of perihelia lying between 155.9-160 degrees and latitudes of perihelia between 4.2-5.7 degrees. Semimajor axes are between 2.23-2.28 AU and indeed overlap with the 7: 2 resonance. Eccentricities are in wide range 0.80-0.90. The most eccentric orbits with lowest perihelion distances were encountered at the beginning of the activity period. The orbits form a concentric ring in the inner solar system. The masses of the observed meteoroids were in a wide range from 0.1 g to more than 1000 kg. We found that all meteoroids larger than 300 g were very fragile (type IIIB), while those smaller than 30 g were much more compact (mostly of type II and some of them even type I). Based on orbital characteristics, we argue that asteroids 2015 TX24 and 2005 UR, both of diameters 200-300 m, are direct members of the new branch. It is therefore very likely that the new branch contains also numerous still not discovered objects of decameter or even larger size. Since asteroids of sizes of tens to hundreds meters pose a threat to the ground even if they are intrinsically weak, impact hazard increases significantly when the Earth encounters the Taurid new branch every few years. Further studies leading to better description of this real source of potentially hazardous objects, which can be large enough to cause significant regional or even continental damage on the Earth, are therefore extremely important.