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Motion of the Dangerous Asteroid 1997 XF11

100%

Sitarski G.

tom Vol. 49, No. 1

103--112

Minor planet 1997 XF11, discovered in December 1997, is moving in the heliocentric orbit which almost intersects the Earth orbit. In October 2028 the asteroid will approach the Earth to within 0.006 a.u. We improved the asteroid's orbit on the base of 151 astrometric observations from 1990-1998. To investigate the long-term motion of the asteroid we randomly selected 500 sets of orbital elements and numerically integrated the equations of motion by the recurrent power series. We followed evolution of minimum distances between orbits of 1997 XF11 and the Earth for moments of consecutive passages of the asteroid through its descending node. We found that only in 2042 the minimum distance between orbits of both planets could be smaller than the Earth radius. However, the asteroid will pass through its descending node in July 2042 while a collision with the Earth could happen during the October encounter. After 2042 the minimum distance between orbits of both planets will be permanently growing up, and hence we estimate that during the next several thousand years collision with the Earth will be impossible. We also investigated the asteroid's motion before 1990. We found that past close approaches of 1997 XF11 to the Earth occurred in 1971 to within 0.032 a.u. and in 1957 to within 0.015 a.u. We calculated ephemerides of the asteroid for those past approaches aiming at finding some old observations of the minor planet. We have also studied accuracy of prediction of the future motion of 1997 XF11 based, however, on 142 observations of the asteroid from 1997/98 only. We found that in that case possibility of collision during 2030-2050, although possible, is completely unpredictable.

Nowe dane na temat wystąpień szkarłupni w wapieniu muszlowym (środkowy trias) Górnego Śląska

41%

Paszcza K.

tom Vol. 72, nr 4

156--161

In the Sadowa Góra quarry in Jaworzno, southern Poland, the Muschelkalk deposits are exposed (Lower and Upper Gogolin Beds). The occurrence of echinoderms seems to be particularly interesting. The isolated ossicles of asteroids were found already in the 1st Wellenkalk of the Lower Gogolin Beds (Aegean), which is one of the oldest post-Paleozoic occurrence in the world. Until recently, it was believed that the first echinoids appeared in the Germanic Basin during the Bithynian (above the Conglomeratic Horizon of the Upper Gogolin Beds). Currently, they have been found, similarly to the remains of asteroids, already in the 1 st Wellenkalk. Attention was also drawn to the fact that the stratigraphically important crinoid species Holocrinus dubius may have appeared in Upper Silesia earlier than previously thought.