The Taurid meteor shower showed significantly enhanced activity in 2015. (Reuters)

The risk of a sizeable asteroid hitting the Earth is significantly growing every few years, warn Czech scientists who analysed 144 fireballs from a recent meteor shower. The Taurid meteor shower showed significantly enhanced activity in 2015. Researchers found that this was due to a well-defined orbital structure. Researchers from the Astronomical Institute of the Czech Academy of Sciences showed that a “new branch” of Taurids contains at least two asteroids of the size 200-300 meters. Since it is likely that numerous of undiscovered asteroids of decameter or even larger size are present as well, impact hazard increases significantly when the Earth encounters the Taurid new branch every few years, researchers said.

The Taurid meteoroid stream produces at least four meteor showers on Earth: two are active at night from the end of September until the beginning of December, and two at day from the end of May to the middle of July. Although comet 2P/Encke is the most probable parent body of the Taurid stream, it was also proposed that 2P/Encke is just a fragment of a much larger comet, which was disrupted thousands of years ago and formed the whole Taurid complex including a number of asteroids. Nevertheless, many of the proposed asteroids may have similar orbits just by chance. In some years, Taurid activity has been higher than usually, especially in terms of large numbers of bright meteors or fireballs. “We performed a careful analysis of 144 Taurid fireballs observed by new digital autonomous fireball Observatories of the European Fireball Network displaced over the Czech Republic at 13 stations, Austria and Slovakia in 2015 when the activity was enhanced,” researchers said.

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Orbits of 113 fireballs show common characteristics and form together a well-defined orbital structure. The masses of the observed meteoroids were in a wide range from 0.1 gramme to more than 1,000 kg. “We found that all meteoroids larger than 300 grammes were very fragile, while those smaller than 30 grammes were much more compact,” researchers said. The newly discovered Taurid branch is a population of bodies with the size range from several millimeters to several hundred of meters, which all move together around the Sun. The narrow range of orbital parameters of the new branch makes the association of Taurids with these asteroids much more reliable than it was possible before. Every few years, the Earth is encountering this branch for a period of about three weeks. During that time, the chance of impact of a sizeable asteroid (tens of meters) is significantly enhanced. Even if intrinsically weak, bodies of such size can penetrate deep in the atmosphere and pose a hazard to the ground.