Blink and you missed it: Asteroid came within 90,000 km, only one sky-watcher saw it
SONEAR sees 25-metre-plus rock when it was, well, so near
A small asteroid made a rare, close pass between Earth and the moon on August 28.
2016 QA2 is estimated by the Minor Planet Center (MPC) as being somewhere between 25 and 55 metres in diameter – so small that it nearly passed without notice.
The MPC's note about the asteroid attributes its discovery to Brazil's SONEAR Observatory, which made this Facebook announcement on August 27.
Its size was calculated as being between 25 and 55 metres – and that puts it as larger than the object that exploded in the atmosphere over Chelyabinsk in February 2013, breaking windows and injuring more than 1,000 people.
The A-type asteroid (named after 2062 Aten, which has a similar orbit; there are around a hundred such) won't be a stranger: it's got a near-Earth orbit, which will make it easy enough to watch out for, now.
The orbit is tilted 15.65° relative to Earth's orbit, and an eccentricity of 0.21, which the announcement says sends it between around 115,000,000 km and 177,000,000 km from the Sun, on a 350-day period.
The SONEAR announcement says it passed us by at a distance of 86,000 km.
This pass was harmless, but if SONEAR's current characterisation of 2016 QA2's orbit is correct (more observations will be made, we're certain), it will come very close one day: “the minimum distance between the orbital 2016 QA2 and the earth is only 60 miles away” – or a bit over 95 km.
SONEAR doesn't mention when that's likely take place; a much more reassuring number comes from NASA's Jet Propulsion Laboratory, which gives the minimum orbit intersection distance (MOID) as 0.00037 astronomical units – or 55,000 km.
Regarding whether or not "60 miles" is a translation error – it may well be, but the translation was provided on SONEAR's Facebook announcement.
Regarding the headline, "only one sky-watcher saw it" – other observations seem to have been made after the fly-by.