Friday, February 5, 2016
Certain of uncertainty for near earth asteroids
In my continuing efforts to de-mystify the art of Asteroid Astrometry, I thought I'd follow up last week's article on about 2016 BE with a deeper examination of the Uncertainty parameter when its listed in orbital elements. This week there is some attention on 2013 TX68 which will possibly make a record close pass of 11,000 klms or possibly be 40 times further away than the moon on March the 5th. I can see that puzzled look on your face ;-) 2013 TX68 is also a Virtual Impactor in 2017, a term we discussed last week. So firstly lets get some perspective on this uncertainty thing. 2011 CF66 was also listed as a virtual impactor for Feb 2nd 2016, it didn't hit us, no-one was worried if it would, and in fact no-one has any idea where it actually is. It is only a tiny asteroid about 3-9m in diameter and wouldn't have done any damage even if it did. In fact there are 20 other virtual impactors listed in the Risk Table this year, the next one might approach on Feb 18th, is 2009 VZ39, and is slightly smaller than 2013 TX68. 2009 VZ39 is also in the daytime sky and not observable for follow up and further confirmation. I only highlight this to emphasise the point here - all asteroids once they are discovered need to be tracked for sometime, to improve the precision of the orbit before any pronouncements about where they are going to be at a certain point in time. The difference between 2013 TX68 and 2009 VZ39 for example is that 2013 TX68 was observed for 31 data positions (astrometry) over 3 nights where as 2009 VZ39 was observed on only one night with 8 astrometric data positions. If you look at the orbital elements for 2013 TX68 the uncertainty parameter is listed as 7, where as for 2009 VZ39 there is not even enough data to start that calculation. For 2011 CF66, there is a 1.1e-8 chance of a collision between 2016 and 2114, so its mathematically possible, but highly unlikely. NASA/JPL produced this nice graph with it's press release this week which illustrates the point well.