Asteroid 2004 BL86 wizzed by the earth at 8:19 a.m. PST (11:19 a.m. EST) at a distance of about 745,000 miles (1.25 million km) — roughly three times the distance of the Moon from the Earth.
And it had a surprise for everyone. According to NASA and JPL, BL86 has a moon. JPL provided an animation of 20 different radar images that show the moon, as well as some detail of the Asteroid's surface.
The 20 individual images used in the movie were generated from data collected at Goldstone on Jan. 26, 2015. They show the primary body is approximately 1,100 feet (325 meters) across and has a small moon approximately 230 feet (70 meters) across. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons). The resolution on the radar images is 13 feet (4 meters) per pixel.
Sort of reminds me of The Siphonaptera:
Big fleas have little fleas upon their back to bitem. Little fleas have lesser fleas, and so ad infinitum.
(Score: 2) by VLM on Wednesday January 28 2015, @04:56PM
thats no moon, thats a lure to attract tasty space ships to land in the depths and find out that its the mouth of a giant space worm thing. Giant space worms are pretty creative and like the taste of curious scientists, hence all the effort to dangle a lure out there.
(Score: 0) by Anonymous Coward on Wednesday January 28 2015, @04:58PM
Haha you old twat, came here to tell the same joke!
(Score: 2) by Immerman on Thursday January 29 2015, @01:02AM
And here I thought it was an alien mothership disguising itself as a moon to avoid raising suspiscions until it was too late to defend against the invasion.
(Score: 2) by Covalent on Wednesday January 28 2015, @11:22PM
I'm surprised that such a small body (the main asteroid) could hold such a REALLY small body (the moon) in the inner solar system. I wouldn't be surprised if this "moon" got either ejected by Earth / Sun / Jupiter or else collides with the main asteroid.
Really cool, though.
You can't rationally argue somebody out of a position they didn't rationally get into.
(Score: 3, Informative) by Nesh on Wednesday January 28 2015, @11:35PM
there's a whole bunch of asteriods that manage to hold onto a moon: see Asteroids with Satellites [johnstonsarchive.net], but I agree on the coolness factor.
(Score: 2) by Covalent on Thursday January 29 2015, @12:53AM
Wow. I learned a new thing! Thanks for the link. I knew a fair number of asteroids in the belt were binaries (or gravitationally linked, or whatever), but I didn't realize that those closer to Earth and the Sun also were often binaries, though I guess it makes sense. It still seems likely to me that this close interaction with the Earth would affect the two bodies differently and potentially dislodge the moon. We didn't know it was there until it was really close...but now that we know what to look for maybe we can keep tabs on it.
You can't rationally argue somebody out of a position they didn't rationally get into.
(Score: 2) by Immerman on Thursday January 29 2015, @12:59AM
You have to pass *really* close to a planet for there to be enough tidal forces to accelerate the asteroid and it's moon at different enough rates to decouple them. At any significant distance (many multiples of the asteroid-moon distance) the acceleration is almost perfectly uniform and won't have much effect on the moon's orbit. While it may get nudged around a bit, on average the tidal forces of various planetary passes will cancel each other out.
Now if the asteroid were actually orbitting a planet or large moon instead of just briefly passing by that would likely change - over time orbital resonance would almost certainly nudge the moon out of its orbit and let it be captured by the larger body instead.
(Score: 3, Informative) by c0lo on Thursday January 29 2015, @04:52AM
Then, you may also be surprised to learn that not even Earth "holds" the Moon on its orbit: it just happens that both of them orbit the Sun and influences each other trajectories.
The reason stays in the Sun's pull on the Moon being greater than the Earth's pull on the Moon: this is why the Moon's orbit around the Sun is convex [harvard.edu] (the cited article is in the Journal of the Royal Astronomical Society of Canada and is as old as 1912)
This is why the distance between Earth and Moon increases over time [wikipedia.org]at an average rate of 3.8 cm per year (for a "captive" Moon, the energy dissipation cause by the tides would cause the Moon to "fall" on the Earth).
Similarly, I suspect this is also the case for the two asteroids (give the comparative sizes of the two asteroids, their relative distance and the weakness of gravitational interaction): they just orbit the Sun together.
Which is not that surprising, actually; it is highly possible the two asteroids are two fragments which suffered a "gentle divorce" from what once was a single asteroid (think of a pre-existing fracture line and an impact of a small but speedy meteorite. Or maybe it was the tidal force acting while the asteroid passed too close to a planet, maybe even the last Earth passage caused it?)
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 1) by Nesh on Wednesday January 28 2015, @11:30PM
so it's not that uncommon. Also see this 'Ask an astronomer' page at caltech Can asteroids have moons? [caltech.edu]
(Score: 0) by Anonymous Coward on Friday January 30 2015, @01:08AM
The Moon is the (natural) satellite of the earth. There is only one Moon.
(Score: 0) by Anonymous Coward on Friday January 30 2015, @09:12AM
Can you spot the difference
The Moon
a moon