(111298) = 2001 XZ55 versus 2008 YL20

See an update about this case received on Dec 10th: look at this MPML msg.



===============================================
I am looking again at these two asteroids.

A couple of years ago, as clearly explained by Bill Gray (see MPML msg ), it was a bit too early to make meaningful simulations trying to go back in the past as far as about 25000 years ago.

Now the orbit uncertaintly of asteroid 2008 YL20 has improved from +/- 1.62e-6 degrees /day to +/-1.1568e-08 degrees/day.

I tried a new simulation to investigate the possibility that these two asteroids separated in the past and I got a new result consisting in a nominal distance of about 4000 km, relative velocity about 15 cm/s. This event occurred about 34000 years ago.

The uncertainty is 1.1568e-08 * 365 * 34000 = 0.14 degrees that at an average distance of 2.39 AU corresponds to an uncertainty of about 0.0057 AU (i.e. three time the moon-earth distance).

So ... on one side no proof that these asteroids separated but it seems to me that this pair is still interesting.

More details looking the JPL Small Body Data:

(111298) = 2001 XZ55
Orbital Elements at Epoch 2457200.5 (2015-Jun-27.0) TDB
Reference: JPL 11 (heliocentric ecliptic J2000)

Element	Value	Uncertainty (1-sigma)	Units
e	.1837905901861221	6.7074e-08
a	2.391320808768463	2.2177e-08	AU
q	1.951818546000553	1.6999e-07	AU
i	3.192061836722895	7.0356e-06	deg
node	111.491991193275	0.00011791	deg
peri	297.8338388091076	0.0001197	deg
M	257.5887075379197	2.2491e-05	deg
tp	2457584.738198736595 (2016-Jul-15.23819874)	8.7199e-05	JED
period	1350.688466278188 3.70	1.879e-05 5.144e-08	d yr
n	.2665307426456207	3.7078e-09	deg/d
Q	2.830823071536374	2.6253e-08	AU

2008 YL20
Orbital Elements at Epoch 2457200.5 (2015-Jun-27.0) TDB
Reference: JPL 8 (heliocentric ecliptic J2000)

Element	Value	Uncertainty (1-sigma)	Units
e	.1837937583380851	5.5869e-07
a	2.391150352530784	6.9177e-08	AU
q	1.951671842487714	1.3831e-06	AU
i	3.193600462494826	1.3927e-05	deg
node	111.4717983197325	0.00025271	deg
peri	298.0606134273407	0.00030036	deg
M	320.5524746963916	0.00012064	deg
tp	2457348.487835047940 (2015-Nov-21.98783505)	0.00045708	JED
period	1350.544050792078 3.70	5.8608e-05 1.605e-07	d yr
n	.2665592431352864	1.1568e-08	deg/d
Q	2.830628862573854	8.1891e-08	AU

Mercury Simulator Results

Simulation parameters:

 algorithm (MVS, BS, BS2, RADAU, HYBRID etc) = bs2
 start time (days)= 2457387.5
 stop time (days) = -17.3d6
 output interval (days) = 20
 timestep (days) = 0.1
 accuracy parameter=1.d-12

The result shown as a graph (done with R package):

Kind Regards,
Alessandro Odasso



      Mercury Simulator - Mercury6
      J.E.Chambers (1999) ``A Hybrid
      Symplectic Integrator that Permits Close Encounters between
      Massive Bodies''. Monthly Notices of the Royal Astronomical
      Society, vol 304, pp793-799.