A Discourse on 1997 XF11
B.G. Marsden (1999), JBIS, 52, 195-202
With a perihelion distance of 0.75 AU (astronomical unit, defined as essentially the mean distance from the Earth to the Sun) 1997 XF11 was indeed an NEA, more specifically the 212th known “Apollo asteroid”, in deference to the 1932 prototype that was the first asteroid known to pass inside the Earth’s orbit . It was the 445th NEA, a broad category that also includes the Amors (with perihelia currently somewhat outside the Earth’s orbit) and the Atens (with orbital semimajor axes smaller than that of the Earth). The NEA category is, in fact, almost too broad to be useful in considering the danger to the Earth from asteroidal impacts. The category includes orbits that have no possibility of bringing their occupants anywhere near the Earth in 10 millennia or more, as well as objects that are as small as 10 metres across and would not survive passage through the atmosphere and be any kind of hazard to the Earth.