[amiralul]

Other source[1] says 0.0002 AU, still very close (about 40,000 km).

[1]: https://cneos.jpl.nasa.gov/scout/object/ZTm0038

[lucb1e]

This, as I understand it, being the closest approach to our orbit, not our atmosphere or so. To put this in perspective, the Earth is some 6.4 Mm in radius, so that's 40-6.4 = 33.6 Mm above the surface.