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3. The 1998 OX4 virtual impactors

We apply the method described above to the lost asteroid 1998 OX4. Attention was focused on this object after we announced that it has a remote, but not negligible impact probability. It was discovered on July 26, 1998 (UT) by Jim Scotti with the 0.9-m Spacewatch telescope on Kitt Peak [MPEC 1998-O27], and observed only over a short arc, due its intrinsic faintness and unfavorable observing conditions [MacMillan 1999]. The keplerian orbital elements with RMS uncertainty at epoch 1999 Jan 22.0 TDT are: semimajor axis $1.581\pm 0.029$ AU, eccentricity $0.486\pm 0.014$, inclination $4.53\pm 0.16$ degrees, longitude of ascending node $300.23\pm 0.15$ degrees, argument of perihelion $116.549\pm 0.035$ degrees, mean anomaly $35.57\pm 0.88$degrees. The object is already lost by several degrees, and the large uncertainty in semimajor axis implies that the length of the confidence region will continue to grow rapidly.


Andrea Milani