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New Temporary Moon in Earth Orbit
On February 15th 2020 a magnitude 20 object designated 2020 CD3 was observed and projected to be in a 47 day elliptical orbit of the Earth. Projections do not all agree yet, but the orbit is believed to be unstable and should not last more than about 3 years. 2020 CD3 is estimated to be between 1 and 6 meters in diameter, though reportage varies wildly on the size estimates. Nobody seems to be commenting on perigee, though the simulation images suggest it is approximately at lunar orbit distance - of course with the 47 day period apogee is well beyond lunar orbit.
This is only the second "captured asteroid" to be observed in Earth orbit, 2006 RH120 was observed to be in Earth orbit from September 2006 to June 2007 - although 1991 VG was weakly captured for a month in 1992 and is expected to return in the future.
Many stories have already been published elsewhere - Wikipedia has already been updated; but, nobody seems to be asking the important questions like: if Pluto can be disqualified as a planet, how can 2020 CD3 be called a moon? ;-) EarthSky was unable to be consulted, perhaps due to the traffic spike, but other astronomers have referred to the object as a TCO - Temporarily Captured Object, while some question if 2020 CD3 is in fact an artificial object like a spent Apollo era booster stage.
Earth has a new mini-moon -- but it's only temporary
"Earth has captured a tiny object and pulled it into orbit.
The asteroid, known as 2020 CD3, is only the second asteroid known to orbit Earth. And while it won't last, this asteroid acts as a temporary mini-moon whirling around our planet."
--The article doesn't expand on why its' orbit is only temporary so I can only imagine that its' orbit is not stable for....reasons.
"In this case, they found a natural satellite that was pulled into Earth's orbit three years ago. "
The article does not say WHEN the orbit may end and... will likely be pulled into collision vector with Earth?
"The asteroid is likely between 6.2 feet and 11.4 feet in diameter, the researchers said on Twitter."
VERY mini-me!
https://www.cnn.com/2020/02/26/world/earth-mini-moon-asteroid-scn-trnd/index.html
(Score: 1, Informative) by Anonymous Coward on Thursday February 27 2020, @06:25AM (2 children)
Objects usually don't get captured just because they happened to wander past. They get captured by having a close encounter with another moon that was already orbiting. Since orbits repeat, it's no surprise that the orbit is in the vicinity of the Moon. Since they also know that the Moon had to be there at the same time as the new object, this is probably how they're able to determine when the object was captured.
It's in a temporary orbit because an orbit that passes so close to a larger object can't be stable. The next time it comes close to the Moon, the gravity of the Moon will change its orbit and it will either crash into the Moon, be thrown out into interplanetary space, or possibly crash into the Earth (but it's much too small to pose any danger). It's also possible that it might be tossed into a different Moon-crossing orbit, but sooner or later it will have another encounter with the Moon, and the process will repeat. Depending on the exact parameters of the orbit, it might be possible for the object to find its way into a stable orbit, but it's really unlikely.
(Score: 0) by Anonymous Coward on Thursday February 27 2020, @06:34AM (1 child)
Once you have 3 or more bodies, orbits are complicated. The universe has far more than 3 bodies.
Then add tidal effects, dust, and radiation pressure. Stability is an illusion that we imagine because our lives are short.
(Score: 3, Interesting) by takyon on Thursday February 27 2020, @10:45AM
https://en.wikipedia.org/wiki/Subsatellite [wikipedia.org]
Moons Could Have Stable Subsatellites (aka "Moonmoons") [soylentnews.org]
It hasn't been observed (yet) even as a human illusion.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]