Friday, November 4, 2011

Asteroid 2005 YU55 will Not Hit the Earth (but you knew that)

Left image: Simulation of Earth as seen from 2005 YU55 at closest approach. Right Image: Simulation of the Moon as seen from 2005 YU55 at closest approach to Earth. Simulated in Celestia (Click to embiggen).

Now that comet 2010 X1 Elenin is a handful of dust, the Doomsayers have had to find a new object to panic about. They have found it in the form of the asteroid 2005 YU55. This 400 meter chunk of rock is now the focus of their inchoate fears. It has eclipsed the previous doom asteroid, Apophis, which is of a similar size, for the moment, despite not being on the list of potentially hazardous asteroids.

As with Elenin, this panic is largely due to people not appreciating the scale of the solar system. In comparison to the distance between the Sun and Pluto, YU55's upcoming encounter with Earth is close. But the asteroid comes no closer than 85% of the distance between the Earth and the Moon (350,000 km). In contrast, Apophis will come within the orbits of geosynchronous satellites in 2029, (12,000 km, over 20 times closer) and will not hit us. Heck, earlier this year 2011 MN skimmed above the geosynchronous satellite zone without hitting us. And back in 1976 2010 XC15 came within 0.5 Earth-Moon distances without hitting us.

Left image: Orbit of 2005 YU55 at closest approach as seen from above. Right Image: Orbit of 2005 YU55 at closest approach as seen from the side. The asteroid is significantly above the plane of Earths orbit. Simulated in Celestia (Click to embiggen).

Could we be mistaken about the orbit of 2005 YU55? We have a very good idea of the orbit of this asteroid based on over 700 observations between 2005 and 2010. It's orbit was refined further when it was observed by the Arecbio radio telescope in 2010. Remember, we have a very good understanding of the orbital dynamics of asteroids, thanks to a gentleman called Newton. We are able to send tiny spacecraft across the trackless void to rendezvous with asteroids, something impossible if we could not predict their orbits with high precision.

But let's look at this another way, let's assume that our understanding of the orbit of 2005 YU55 was so bad that it could be within 50% of it's predicted position. Then at its closest it would be about 125,00 km away, well away from us, and no threat of collision.

Chart of the sky as seen from Australia on 9 Nov from astronomical twilight on. Ticks show the asteroids position at half hour intervals. Click to embiggen.

It will be closest to us on November 8, 23:39 UT, this translates out to around 10:30 am AEDST on the 9th in Australia, still from astronomical twilight on the 9th Australian observers will be able to see it scream along low above the northern horizon.

With strong Moonlight, you will need at least a 6" scope to be able to see the 11-12th magnitude asteroid (remember unaided eye visibility threshold is around magnitude 6 without moonlight, and in binoculars under moonlight you are pushing to g below magnitude 8, unless you have super tripod astronomical binoculars), and it moves so fast you will be ale to see it move visibly against the background stars as you watch.

The closeness of the asteroid means that it's elements break most planetarium programs (eg. Stellarium puts the asteroid in completely the wrong position, and SkyMap is a little off). You will have to generate a topocentric ephemeris from the using the MPEC ephemeris generator, if you enter the latitude and longitude of your site, into the box in the ephemeris generator it will create a correct topocentric ephemeris for your site. My GRAS observing tips are here, and more observing tips here.

I've also made a Celestia file for you. As usual, copy the code below and save as it as a file 2005YU55.ssc in the Celestia extras folder.
"2005 YU55" "Sol"
Class "asteroid"
Mesh "ky26.cmod"
Texture "asteroid.jpg"
Radius 0.4 # maximum semi-axis
MeshCenter [ -0.000718 -0.000099 0.000556 ]

InfoURL ""

Epoch 2455800.5 # Epoch 2011 Aug. 27.0
Period 1.22
SemiMajorAxis 1.1427166
Eccentricity 0.4289481
Inclination 0.51346
AscendingNode 39.31601
ArgOfPericenter 268.77407
MeanAnomaly 348.84963

RotationPeriod 0.9

Albedo 0.15



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