The rocky near-Earth asteroid — 3122 Florence — whizzed by Earth September 1 – coasting by at about 18.4 lunar distances – but there was a surprise.
Radar imagery has revealed that the asteroid has two moons, according to the Jet Propulsion Laboratory’s Center for NEO Studies (CNEOS).
Making use of the 70-meter antenna at the Goldstone Deep Space Communications complex, radar images show two moons orbiting the much larger central body, which is about 2.8 miles (4.5 kilometers) in diameter.
The sizes of the two moons are not yet well known, but are likely between 300-1,000 feet (100 – 300 meters) across.
Future impact concern?
This near-Earth object does not often come so close: the asteroid had last been similarly close in 1930, and will not become close to Earth again until 2057.
According to the European Space Agency, while it usually passes our planet at a safe distance, orbital disturbances in the (distant) future “could bring it closer, and the size of the object is such that it could be of future impact concern.”
Found to be round
Florence is only the third triple asteroid known in the near-Earth population out of more than 16,400 that have been discovered to date. All three near-Earth asteroid triples have been discovered with radar observations, notes a CNEOS statement.
Florence reached its closest approach to Earth early on September 1 and is now slowly receding from our planet. The asteroid was found to be fairly round. Also, 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.
Additional observations
Additional radar observations are scheduled at NASA’s Goldstone Solar System Radar in California and at the National Science Foundation’s Arecibo Observatory in Puerto Rico through September 8.
These observations should show more surface detail on Florence and provide more precise estimates of the orbital periods of the two moons. Those results are valuable to scientists because they can be used to estimate the total mass and density of the asteroid.