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.

Image Credit: P. Chodas (NASA/JPL)

What you see is a graphical representation of the "error bars" or the zone of uncertainty, based on the orbit elements that we currently know. This asteroid will be picked up again in future surveys and the zone of uncertainty will reduce further.

Uncertainty Parameter is quite a complex calculation, but it essentially always starts off being a "9" and reduces over ensuing months as more data is collected. Uncertainty is a table of the "Runoff" of arcsecs per decade and Level 7 just means essentially there will be less than 33,121 arcsecs of "runoff" over the next decade. You can think of this as being: in a decade the place to look will be 33,121 arcsecs bigger than the range of uncertainty we need to factor in when we look for it now.

Many of the "click-bait" bloggers and conspiracy theory followers regularly confuse Uncertainty with the Torino Scale - they shouldn't, as even WIKIpedia has a great explanation of the Uncertainty factor, however they google "Asteroid rating 7" and get a hit on what the Torino Scale is and confuse the two, without doing any further investigation. The Torino scale is a risk weighted table and ALL current Virtual Impactors are listed as Torino Level 0. The virtual impactors that are listed have "potential" collisions over a range of years and are only there because we largely don't have enough data yet to remove them.

Asteroid Apophis (99942) 2004 MN4 briefly shot up the Torino Scale to a record high Level 4, before subsequent radar imaging and 4452 observations over 10 oppositions reduced its Uncertainty Parameter to 0 and its Torino Level to 0, with an asterisk that it needs to be carefully watched. Asteroid Apophis will be a naked eye object on April 13th 2029 when it makes a very close but HIGHLY CERTAIN pass of the earth. This level of certainty is only refined by many hundreds of hours of dedicated work from professional and amateur astronomers.

Lastly, Uncertainty should not be confused with don't know, don't care, have no idea what we are doing. Its just a case of not YET having enough data, more needs to be collected.

Asteroid 2015 TB145 (PHA) close and bright flyby Oct 31

UPDATE: Oct 31st, 2015. Live coverage of Asteroid 2015 TB145.

Image Credit: P.Lake 10 Sec image from U69 T24 - travelling at 115 arc"/m at PA 35.4 07:00 UT (Available for media use with attribution to this blog)

Compare the two images - Above a 10 sec image, Below a two minute image which was stacked for movement of the asteroid.

UPDATE: Oct 31st, 2015 - From the NASA Press release this morning the amazing radar images have shown a dark dead comet,(and I am not making this up) looks not unlike a skull. The radar run went well getting down to a resolution of 7 meters per pixel. Its interesting those depressed areas are likely impact craters or collapsed areas from which the jets emerged when the comet was active. Recent studies of 67P by Rosetta have shown collapsed areas on Comet 67P where jets seem to originate from. This comet has been long dead, some studies have already been done to check for past meteor showers originating from its orbit - see the post on the SETI Institute Blog. Also from the press realease: "NASA values the work of numerous highly skilled amateur astronomers, whose accurate observational data helps improve asteroid orbits....". I hope to have more images tonight (weather permitting) - stay tuned.

Image credit: NAIC-Arecibo/NSF

UPDATE: Oct 27th, 2015 - Great set of images last night in the pre-dawn sky from New Mexico. The asteroid has brightened to Mag 15.8 and its apparent speed across the sky is starting to increase as it gets closer. [Also I should probably point out the faint halo you may be able to see is due to the strong moonlight reflecting off some dust on the primary mirror - the full moon was only 36 degrees away]

UPDATE: Oct 24th, 2015 - Finally got some images. The asteroid has brightened considerably to Mag 16.8/9 ish. No signs of cometary activity at this point. Its moving at 0.39arc"/m in a 120 sec image (so 0.78arc" in the image)and the pixel plate scale is 0.53 arc"/pixel so you can see a hint of softness on the trailing side. Definitly no cometary activity though - that's as close as I can go to getting it as sharp as you can get it.

Image Credit: P.Lake 2015 TB145 9x120 secs on the 0.7m Burnell, Cannon, Leavitt Telescope (BCL) T27 at Q62, SSO.

UPDATE: Oct 22nd, 2015 - Getting frustrated, the observatory has been closed due to bad weather for 4 nights.

UPDATE: Oct 17th, 2015 - NASA have updated details of the planned radar runs and expect to be able to get images with a resolution of 2 meters per pixel, they expect it to be the best radar run of the year. Also one other interesting aspect is the Tisserand parameter has been calculated at 2.937 which is just lower than the theoretical "boundary" (of 3.0) between Asteroid and Jupiter Family Comets. The other target of a radar run on 29th is 2009 FD, a well studied Apollo Asteroid, has a Tisserand parameter of 5.295. The seeing was a bit poor on the 14th so the image wasn't strong enough. The relative speed (across the camera chip) will slow to only 0.17 arc"/min on the 19th so I'll be able to stack the images really deep and get a good look at it. If the seeing is better tonight we might even get some more detail. I did look a bit fuzzy the other night but as you can see in the video the satellite that trailed through was very fuzzy as well - so I'm not reading to much into that at the moment.

Image/Video Credit: 2015 TB145 from H06, 12 x 180 sec exp stacked 4x3, 0.5m Planewave October 14th - P.Lake

A couple of times a year, the asteroid surveys throw up a surprise, with a large asteroid approaching very close to the Earth, with little advance notice. After last week's blog post about the Blogsphere overeacting to an Asteroid that astronomers knew about for 15 years passing at 65 Lunar Distances (LD), the "surprise" of course had to happen this week.

This will be an interesting two weeks, as Asteroid 2015 TB145 will cruise by Earth just outside 1 Lunar distance (1.3 LD). The asteroid is a target of the Arecibo Observatory (that big antenna that rose out of the lake in the majestic James Bond scene), and to get some really great radar tracking and detailed images, the ephemeris and position of the asteroid needs very high precision.

To give you an idea of the type of imaging to be obtained (see below), a similar situation occured last year for 2014 HQ124. These were some of the best radar images ever recorded, and some of my data was used to refine the orbit for targeting on that occasion.

Image Credit: Asteroid 2014 HQ124 Radar images from Goldstone - NASA/JPL

This asteroid is twice as big (between 290 and 650 meters diameter - most astronomers are calling it about 480m) and twice as close as 2014 HQ124, so you can only imagine how good the images should be. Professional Observatories and amateur astronomers will be tracking it closely to improve the precision of the orbit as it approaches.

I was quite chuffed when tracking 2014 HQ124 that my light curve had a few bumps in it and I made the call it was "not round" which was subsequently confirmed by the radar images.

So who knows what the next two weeks will turn up? What we know at this stage is that is going to be quite bright and could be visible in binoculars. Also its speed is very fast, but its moving slowly across the images at the moment as you can see, because of the angle its approaching us at. As it makes its close approach its going to do a nice "flyby" of the Crab Nebula M1 for Northern Hemisphere viewers on Oct 29th/30th Ian Musgrave has details on his blog shortly.

So stay tuned, I'll be following it closely and providing some regular updates.