Since before the dawn of history we have admired our planet’s amazing moon and enjoyed its beautiful light.Since the 1600s we have known that some of the other planets of the Solar System have multiple moons.This started some astronomers thinking; perhaps we do have more than one moon!
If we did have a second moon, it would be very small and would need careful observation to spot.In 1846 a French astronomer called Frédéric Petit claimed to have found a tiny second moon in a bizarre orbit which would cause it to swoop to within as low as 12 km of the Earth’s surface every couple of hours.At the time several other Frenchmen backed up Petit’s theory but it was widely dismissed elsewhere.The Petit Moon is an impossibility; air resistance, little appreciated back then, around its perigee would bring it crashing down to Earth.If it really existed, today air traffic would have to be rerouted to avoid it!Today its occasional observations by French astronomers seem to be the result of the Gallic imagination fuelled possibly by fine wines.
Later searches for additional moons of our planet, including one as late as the 1950s by Clyde Tombaugh, sponsored by the USAF, have found nothing in permanent orbits around Earth.What about impermanent satellites?A few years ago, researchers at Cornell University estimated how many “irregular natural satellites” may be temporarily captured by Earth. They concluded that at any given time Earth probably has a second moon. These short-term moons come and go quietly and without being noticed, but at least one was been detected. In 2006 the Catalina Sky Survey in Arizona found a mysterious white object, RH120, rotating around Earth from June 2006 to June 2007. RH120 is so white as to appear artificial, it has been suggested it is actually a Saturn 5 upper stage but this seems unlikely now. This object, roughly 5m long, is now in solar orbit and its next predicted near-Earth encounter is in 2028.
But, just perhaps, briefly the Earth had a second natural satellite seen by thousands of people.Remember the spectacular fireball witnessed over the UK and Ireland on 21 September 2012? It was not alone; later the same evening, in what seemed to be an unrelated coincidence, a fireball passed over south eastern Canada and the north eastern United States. Sky and Telescope‘s website has reported the staggering possibility that these two bolides were one and the same!
Just possibly the meteoroid passed over the British Isles at an altitude of about 50 km and speed of about 13km/s, escaping back to space.It did not get away unscathed; the atmospheric passage took its toll.It clearly broke apart broke apart, it may in fact have been slowed by air resistance to a speed of about 9.2 km/s, too slow to permanently escape Earth .Rather, this amazing theory suggests it became a temporary satellite of Earth, brief atmospheric passage took its toll.As the meteoroid broke apart, its velocity dropped to just 5.7 miles (9.2 km) per second, too slow to make an escape back to space.Instead, it became a temporary satellite of Earth, making a complete orbit before re-entering the atmosphere for a second and final time over North America two and a half hours later.In those two and half hours we had a second moon!
(Article by Colin Johnston, Science Communicator)