Asteroid Florence or more properly 3122 Florence (1981 ET3) was discovered by Schelte “Bobby” Bus at Siding Spring Observatory in Australia in March 1981 and named for Florence Nightingale made a “close” flyby on 01 September 2017.
The actual distance of the flyby was (about) 7,065,270 km / 4,390,155 miles which is close enough for an object that has a diameter of 4.5 km / 2.8 miles. Also close enough to get nice radar images using the 70-m antenna at the Goldstone Deep Space Communications Complex (Images: NASA).
To almost everyones surprise Florence has two moons which makes Florence a triple asteroid system. There are now three known “triples” in the population of 16,400 asteroids and the other two were also discovered by radar, the last discovery was asteroid named 1994 CC made in 2009.
NASA — “The sizes of the two moons are not yet well known, but they are probably between 100 – 300 meters (300-1000 feet) across. The times required for each moon to revolve around Florence are also not yet known precisely but appear to be roughly 8 hours for the inner moon and 22 to 27 hours for the outer moon. The inner moon of the Florence system has the shortest orbital period of any of the moons of the 60 near-Earth asteroids known to have moons. In the Goldstone radar images, which have a resolution of 75 meters, the moons are only a few pixels in extent and do not reveal any detail.
The radar images also provide our first close-up view of Florence itself. Although the asteroid is fairly round, it has a ridge along its equator, at least one large crater, two large flat regions, and numerous other small-scale topographic features. The images also confirm that Florence rotates once every 2.4 hours, a result that was determined previously from optical measurements of the asteroid’s brightness variations.”
An orbital period of 2.35 years should allow for subsequent observations in future encounters. Speaking of close encounters, we will have a VERY CLOSE encounter with asteroid 2012 TC4 on October 12 when it will pass just 0.13 lunar distances away, that’s only 49,972 km / 31,051 miles!
Edit: Sorry about the late posting, operator error.