The asteroid that was confirmed as a NEO, set to make a close approach of less than 0.2 lunar distances to Earth, which was given the provisional designations 2015 YB only to have its confirmation retracted, as been confirmed as a Hungaria asteroid (a type of Inner Main-belt object) and given the provisional designations 2015 YU9. The story of the close approach has echo across social media. However, the story that was missed by many is a story how science works.
First Background on observing asteroid (and comet).
In the world of asteroid (and comet) observing a series of images of the sky is taken over period of time with telescope and CCD. Then data reduction is done on the images looking for moving object. The observer makes two or more observation for each moving object. All “known” objects have a designation, if the observer knows the object’s designation the observation are made under their designation. If it is an unknown object or in doubt an observer-assigned temporary designation is use. The Minor Planet Center’s computers check any observer-assigned temporary designation to see they are “known” objects, if any are unknown and “their NEO score is 65” are posted to “The NEOConfirmation Page”(NEOCP) .
Many observers watch the NEOCP and do follow-up observation on listed objects. As more observational data comes in better orbital elements can be generated, the "unknown" object maybe shown to be a "known" object or shown to be "new" object. When there is there is enough observation to generate useful orbital elements the object is assigned a provisional designation by the Minor Planet Center, if the object is a NEO, a comet, or unusual a Minor Planet Electronic Circulars will be issue. It is possible over time with additional observational data two or more provisional designations maybe link showing there are the same object. After four well observed oppositions for main-belt (two to three for NEOs) asteroids are number (their permanent designation).
The great thing about asteroid and comet observing is your work is a cross check and will be cross check by the work other observers. A scary about asteroid and comet observing is your work is a cross check and will the work is cross check by other observers. Therefore asteroid and comet observing requires healthy sense of pride in one work tempered by healthy sense humility. As an observer I enjoy seeing additional observations of objects I follow and dread not seeing any additional observations of objects I followed.
A case of dread is in 2015 I reported observation using the observer-assigned temporary designation SMT000I (from H06) they where link to observations of a NEOCP object from G45 and assigned the provisional designations 2015TJ237 (Orbit type: Mars-crosser) I have been unable observe 2015 TJ237 and no one has observed 2015 TJ237 since my observations. I think the observations of 2015 TJ237 from G45 should belong to (440043) 2002 QF24 (Orbit type: Mars-crosser). When all is said and done observing is done by (or at the direction) of humans and can be subject to errors and other observers can catch the errors.
Now Back to 2015 YB
2015 YB was not an ordinary asteroid, it was to make a close approach of less than 0.2 lunar distances to Earth so many observers where looking for it where it "should" be and did not find it so the errors where found and the confirmation was retracted. The object was then returned to the NEOCP under its observer-assigned temporary designations. I have looked the object when it was 2015 YB so had to find it. I was able to image the object make observations and report the observations. Other observers also report the observations of the object. On 2015-12-31 the Minor Planet Center made a notation on a cross-reference page stating the object was assigned the provisional designations 2015 YU9 when MPEC 2015-Y95: DAILY ORBIT UPDATE (2015 DEC. 31 UT) was issue it list its orbit (Orbit type: Hungaria)
- Notes on how to begin your own astrometric program (The Minor Planet Center)
- JPL Orbit Diagram 2015 YU9