Selected OrbFit impact solutions for asteroids (99942) Apophis and (144898) 2004 VD17

During the Meeting on Asteroids and Comets in Europe - in May 12-14, 2006 in Vienna - there have been presented certain results of computations of possible impacts of (99942) Apophis and (144898) 2004 VD17 on the Earth. These results were obtained from computations performed with the use of OrbFit software. The results were then compared with impact solutions presented by the JPL Sentry System and by NEODyS CLOMON2. In all author's computations two version of the OrbFit Software, Package: 3.3.1 and Package 3.3.2, were used. These packages are free downloadable from http://newton.dm.unipi.it/neodys/astinfo/orbfit/.

The influence of relativistic effects, radar observations, the number of additional perturbing asteroids, different JPL Ephemeris of Solar System and use of the multiple solution method were investigated. It became apparent that the greatest influence on computation of the exact impact solutions have relativistic effects and the close approaches of massive asteroids with (99942) Apophis and (144898) 2004 VD17. With the use of the free OrbFit software and its source code almost the same results of possible impact solutions for (99942) Apophis and for (144898) 2004 VD17 as those given on the NEODyS www page were obtained. Additionally, it was possible to change the output format and the kind of output results. The OrbFit is an interactive software which requires some knowledge of celestial mechanics as authors say.