Three months after its discovery on 6 December 1997 by James V. Scotti of the University of Arizona's Spacewatch Project, the asteroid was predicted to make an exceptionally close approach to Earth on 28 October 2028. Additional precovery observations of the asteroid from 1990 were quickly found that refined the orbit and it is now known the asteroid will pass Earth on 26 October 2028, at a distance of 929,000 km (2.42 LD).[3][14][15] During the close approach, the asteroid should peak at about apparent magnitude 8.2,[16] and will be visible in binoculars.[17]
1997 XF11 measures between 0.7 and 1.4 kilometers in diameter.[6][4][5]
This asteroid also regularly comes near the large asteroid Pallas.[15]
IAU Circular
On 11 March 1998, using a three-month observation arc, a faulty International Astronomical Union circular and press information sheet were put out that incorrectly concluded "that the asteroid was 'virtually certain' to pass within 80% of the distance to the Moon and stood a 'small...not entirely out of the question' possibility of hitting the Earth in 2028."[18] But by 23 December 1997, it should have been clear that XF11 had no reasonable possibility of an Earth impact.[18] Many news outlets mistakenly emphasized the possibility of disaster.[19]
Within hours of the announcement, independent calculations by Paul Chodas, Don Yeomans, and Karri Muinonen had calculated that the probability of Earth impact was essentially zero, and vastly less than the probability of impact from as-yet-undiscovered asteroids.[18] Chodas (1999) concurs with Marsden (1999) that based on the 1997 data alone there was about 1 chance in a hundred thousand that XF11 could have been on an Earth-impact trajectory—that is, until the 1990 precovery observations eliminated such possibilities.[20] During the October 2002 close approach, the asteroid was observed by the 70-meter Goldstoneradar dish, further refining the orbit.[17]
History of close approaches of large near-Earth objects since 1908 (A)
(A) List includes near-Earth approaches of less than 5 lunar distances (LD) of objects with H brighter than 18. (B)Nominal geocentric distance from the Earth's center to the object's center (Earth radius≈0.017 LD). (C) Diameter: estimated, theoretical mean-diameter based on H and albedo range between X and Y. (D) Reference: data source from the JPL SBDB, with AU converted into LD (1 AU≈390 LD) (E) Color codes: unobserved at close approach observed during close approach upcoming approaches
^Martinez, Vicente Mas; Silva, Gonzalo Fornas; Martinez, Angel Flores; Garceran, Alfonso Carreno; Mansego, Enrique Arce; Rodriguez, Pedro Brines; et al. (October 2016). "Lightcurves for Two Near-Earth Asteroids by Asteroids Observers (OBAS) - MPPD: 2016 April-May". The Minor Planet Bulletin. 43 (4): 283–284. Bibcode:2016MPBu...43..283M. ISSN1052-8091.
^Warner, Brian D. (October 2016). "Near-Earth Asteroid Lightcurve Analysis at CS3-Palmer Divide Station: 2016 April-July". The Minor Planet Bulletin. 43 (4): 311–319. Bibcode:2016MPBu...43..311W. ISSN1052-8091.
^Slivan, Stephen M.; Bowsher, Emily C.; Chang, Bena W. (December 2002). "Rotation period and spin direction of near-Earth asteroid (35396) 1997 XF11". The Minor Planet Bulletin. 30 (2): 29–30. Bibcode:2003MPBu...30...29S. ISSN1052-8091.
^Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 – Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. S2CID53493339.
^Pravec, Petr; Harris, Alan W.; Kusnirák, Peter; Galád, Adrián; Hornoch, Kamil (September 2012). "Absolute magnitudes of asteroids and a revision of asteroid albedo estimates from WISE thermal observations". Icarus. 221 (1): 365–387. Bibcode:2012Icar..221..365P. doi:10.1016/j.icarus.2012.07.026.
