Selection from the Planetary Society blog entry...
On the heels of the news last week that the Rosetta spacecraft was spotted by sky surveys and briefly named among the minor planets as 2007 VN84 came another close approach by a newly discovered near-Earth object, designated 2007 VF189, which had an orbit surprisingly similar to the Rosetta spacecraft, making a close approach to Earth (closer than the Moon, about 250,000 kilometers away) roughly six hours after Rosetta, on November 14. This is a story that has been unfolding on the Minor Planets Mailing List, and I've been watching it with interest. (A big thanks to all of the various MPML participants whose comments I'm paraphrasing below, in particular Richard Kowalski -- whose Catalina Sky Survey discovered both 2007 VN84 and 2007 VF189 -- as well as Steven Chesley and Alan Harris.)
In brief: the probability for there to be a random object so close in the sky to Rosetta is 1 in 70; the probability for Rosetta and this object to come close to Earth within 6 hours of each other is 1 in 10; and the probability that they would have velocities within 2.1 km/sec of each other is 1 in 10. Multiplying those together, you get a 1 in 7000 chance for Rosetta and another object to pass so close to each other, at nearly the same speed, near Earth. That's an interesting number, because it's not too likely, but neither is it vanishingly unlikely. Plenty of people bet lots of money on worse odds.
In the end, then, 2007 VF189 is a small, unremarkable Apollo-class object (meaning it's an Earth-orbit-crossing asteroid with an orbital period of longer than one year), and nobody would have paid much attention to it if not for last week's mixup.
"Son of Rosetta"
The Planetary Society Weblog
By Emily Lakdawalla
16 November 2007
Link: Article
Link: JPL Small-Body Database Browser for 2007 VF189
Link: Minor Planet Center data for 2007 VF189
Link: Article from Der Spiegel, Thorsten Dambeck, 15 November 2007, "Unknown flying object pursues space probe "Rosetta"
Link: Translation of Above Der Spiegel Article
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