The discovery of P/2001 Q11 (NEAT)

During the course of my search for precovery images of known comets on Jan. 27, 2010, I came across a cometary object in NEAT-Palomar images of Aug. 18, 2001. As one can see from the images below, the object showed a clear tail:

Animation of the NEAT triplet of Aug. 18, 2001

Stack of the NEAT triplet of Aug. 18, 2001

However, I did not panic, since I have come across such objects quite often and either they turned out not to be real or already known. So I did a check to see whether a known comet or asteroid was near this position at this time. When this search turned out negative I started to become a bit nervous... ;)

I calculated a Vaisälä orbit and was quite surprised to see possible NEAT candidate images close to the first one. And indeed, the next images, taken by NEAT-Haleakala of Aug. 22, showed this object, but only in two images with one of it involved with a star. But the single one also showed the tail:

Single NEAT image of Aug. 22, 2001

The next steps were quite easy. With the new positions I improved the orbit and was able to find more and more images/positions. In the end the arc was extended until mid-December 2001! Missing NEAT images were later kindly provided by Dr Steven Pravdo of the NEAT project, which helped to complete the dataset.

After I had collected my data and was looking at the resulting orbit, I was finally sure that it was a comet. It had a Jupiter MOID of about 0.65 AU, and indeed it had an approach with Jupiter before its next perihelion in 2007, which caused the perihelion distance to increase by about 0.1 AU. However, this 2007 perihelion looked favourable and I tried to detect any matches in the MPC ONS file. However, nothing was found.

After I had sent in the data and Brian Marsden detected the single LONEOS observation of October 24, we wondered whether other surveys might have imaged the object without measuring it. However, again no success. Robert McNaught checked Siding Spring Survey images of July 2007, which covered the expected position of the comet, but nothing was seen. The comet was too faint, maybe due to the larger perihelion distance or maybe due to the fact that it was unusually active in 2001. Checks of LINEAR data also proved not successful, and a check by Andrea Boattini of Catalina and Mt. Lemmon images showed that these surveys missed the comet always by a few degrees.

The comet was finally reported in IAUC 9129, and MPEC 2010-F38.

So, why was the comet not discovered in 2001? I think the main reason is that it was automatically detected and measured and nobody really looked at the images. If this would have happened, it would have been identified as a comet and quickly followed up. The reason that the comet was not again automatically detected by NEAT is due to the fact that of the usual NEAT triplets often only two or even one were of good quality and thus did not qualify for reporting. Add to that the fact that after August the next detection was in October, quite a large gap to get a succesful automated linkage. If the object would have popped up at the NEOCP things would have looked different.

Below I give the orbits for 2001, 2007, 2014 and 2020. The 2014 apparition is extremely unfavourable and I really hope for a recovery in 2020, when things look much better.

P/2001 Q11
   Perihelion 2001 Jun 22.351249 TT =  8:25:47 (JD 2452082.851249)
Epoch 2001 Jun 22.0 TT = JDT 2452082.5   Earth MOID: 0.8585   Ju: 0.6466
M 359.94399              (2000.0)            P               Q
n   0.15944594     Peri.  202.27309      0.96904880      0.15291484     
a   3.36816791     Node   147.01234     -0.13601297      0.98586974     
e   0.4502563      Incl.   20.85256     -0.20602155      0.06839511     
P   6.18           M(T) 15.0    K  10.0   q 1.85162894  Q 4.88470688
From 21 observations 2001 Aug. 18-Dec. 13;   RMS error 0.673 arcseconds

P/2001 Q11
   Perihelion 2007 Nov 24.214439 TT =  5:08:47 (JD 2454428.714439)
Epoch 2007 Nov 24.0 TT = JDT 2454428.5   Earth MOID: 0.9619   Ju: 0.6482
M 359.96695              (2000.0)            P               Q
n   0.15408966     Peri.  207.16753      0.97508896      0.10590201     
a   3.44577595     Node   145.00061     -0.08372486      0.98939114     
e   0.4342601      Incl.   19.86494     -0.20540605      0.09944810     
P   6.40           M(T) 15.0    K  10.0   q 1.94941281  Q 4.94213909
From 21 observations 2001 Aug. 18-Dec. 13;   RMS error 0.673 arcseconds

P/2001 Q11
   Perihelion 2014 Apr 23.096111 TT =  2:18:24 (JD 2456770.596111)
Epoch 2014 Apr 23.0 TT = JDT 2456770.5   Earth MOID: 0.9671   Ju: 0.6491
M 359.98521              (2000.0)            P               Q
n   0.15385281     Peri.  207.39513      0.97530987      0.10342799     
a   3.44931149     Node   144.91931     -0.08108142      0.98954861     
e   0.4334007      Incl.   19.84674     -0.20541772      0.10047976     
P   6.41           M(T) 15.0    K  10.0   q 1.95437719  Q 4.94424579
From 21 observations 2001 Aug. 18-Dec. 13;   RMS error 0.673 arcseconds

P/2001 Q11
   Perihelion 2020 Sep 25.925996 TT = 22:13:26 (JD 2459118.425996)
Epoch 2020 Sep 25.0 TT = JDT 2459117.5   Earth MOID: 0.9960   Ju: 0.6419
M 359.85861              (2000.0)            P               Q
n   0.15268940     Peri.  207.52465      0.97498949      0.10555878     
a   3.46681058     Node   144.67154     -0.08278921      0.98917416     
e   0.4279027      Incl.   19.76880     -0.20625576      0.10194020     
P   6.45           M(T) 15.0    K  10.0   q 1.98335294  Q 4.95026822
From 21 observations 2001 Aug. 18-Dec. 13;   RMS error 0.673 arcseconds
© 2010, Maik Meyer
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