Full moon is this Monday, March 9. As we gaze upon our faithful natural satellite, its orbital routine we have known since man or woman first paid attention to the night sky, we might feel reassured that our home, the Earth, has its one companion, traveling with us on our perpetual journey around the sun. Now we are told, that temporarily, we have a second moon, a very small one that has gone unnoticed for years.
Astronomers at the Catalina Sky Survey have discovered a “mini-moon” that was captured by the Earth. This object is really a boulder, estimated to be six to 12 feet wide.
It’s actually an asteroid that was circling the sun, and was snared by the Earth’s gravity. It might have flown by missing us, or even hit us, but the rock came in such an angle to enter orbit. It had a long, looping orbit that will eventually hurl this visitor back into its solitary former existence, cruising around the sun on its own.
For a while, the Earth has two moons. What we have, however, is a “guest” not unlike when we have a friend come by for dinner. The friend is our guest, not an increase in our household.
Naturally, this guest was never invited, but not that anyone minds. The Earth was just in the right place at the right time, to pick up this stray.
Officially known as 2020 CD3, the captured asteroid was discovered on Feb. 15 by the Catalina Sky Survey. Astronomers Kasper Wierzchos and Teddy Pruyne.
Even in a dark sky and with the average backyard telescope, don’t expect to go out and see our guest moon. 2020 CD3 was exceedingly dim, at +20th magnitude, but was picked up on images taken looking towards the constellation Virgo. The speck of light can be seen darting across the starry field by comparing the images.
It was 186,000 miles away, which is closer to us than our own moon (which averages 238,000 miles away).
Calculations of its orbit, traced back in time, show that 2020 CD3 was captured at some point in 2016 or 2017. There was speculation at first it might have been a discarded rocket booster. Spectra taken and studies of its orbital path show that it isn’t affected by the pressure of solar radiation, as a hollow rocket would be; rather, the object is dense and compact like an asteroid.
2020 CD3 is expected to be ejected from orbit in March or April of this year.
Catalina Sky Survey picked up a mini-moon back in 2006, which eventually was sent on its way. Likely, the Earth has routinely kept company with guest moons, none of which stayed around long enough to be listed as a “dependent” at tax time.
2020 CD3 is Earth’s second mini-moon ever discovered.
Our faithful moon has no competition, anyway. Our moon is 2,160 miles wide, about a quarter the size of Earth. It has, however, been battered by many thousands of asteroids over the eons, which added to its girth and left its amazing array of craters. The Earth too has had many asteroids that have hit, rather than coursing by in close encounter or being captured as a mini-moon.
A rock the size of 2020 CD3, however, would be expected to leave only a small meteorite, most of it vaporizing in atmosphere, should it stop by to stay. The chances of that happening for this rock in the next 100 years is expected to be about 3%.
Catalina Sky Survey, based at the University of Arizona’s Lunar and Planetary Lab in Tucson, Arizona, is a NASA funded project. Its mission is to discover and track near-Earth objects, identifying any potentially hazardous asteroids.
For more information about the Catalina Sky Survey and our mini-moon, visit https://catalina.lpl.arizona.edu.
Keep looking up at the sky!
Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at [email protected]. Please mention in what newspaper or website you read this column.
