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P/2020 F1 (Leonard): A previous-perihelion precovery, and a very, very young comet.

Sam Deen
 

Hi all,

As I expect you guys of all people know, comets are quite volatile objects as Solar System objects go, prone to significant orbital change and even physical change on a single lifetime. One such interesting object is P/2020 F1 (Leonard) announced yesterday in MPEC 2020-F144, and discovered only 10 days ago.

Due to some quite fortunate PANSTARRS precoveries, I was able to find some further precoveries of my own, specifically 4 from this perihelion:

    PK20F010  C2019 01 02.27874307 43 11.64 +18 15 34.2          23.2 G      W84
    PK20F010  C2019 01 11.36867907 38 12.27 +18 34 45.2          22.3 R      568
    PK20F010  C2019 01 11.36986607 38 12.22 +18 34 45.4          22.1 R      568
    PK20F010  C2019 01 11.37106607 38 12.18 +18 34 45.6          22.3 R      568

and much more interestingly, four SDSS images from the last perihelion, taken in 2002:

    PK20F010  C2002 03 05.25084711 37 12.63 +06 46 29.0          20.5 r      645
    PK20F010  C2002 03 05.25167611 37 12.61 +06 46 29.2          20.3 i      645
    PK20F010  C2002 03 05.25333511 37 12.55 +06 46 29.7          19.7 z      645
    PK20F010  C2002 03 05.25416411 37 12.52 +06 46 29.8          21.2 g      645

as far as I'm aware, this is the first time a comet observed for a single perihelion has been precovered in another perihelion period via archival observations alone- and I'm confident in the identity, as it has a tail in the 2002 observations as well:


Out of curiosity, I projected the orbit forwards and backwards a couple of centuries. While over the next couple centuries, it doesn't do anything too drastic as comet perturbations go- between now and 2020 its perihelion distance goes down from 3.98 AU to 3.68 AU, with its aphelion distance similarly decreasing from 9.68 AU to 9.23 AU, and its inclination increases very slightly from 5.44 to 6.13 degrees.

However, going into the past, its orbit shows that it's actually a very recent addition to the Solar System's known comets, less than a century old, even. The chief reason being that it made a close approach to Saturn of only 978,000 +/- 65,000 km (only 17 +/- 1 Saturn Radii, closer than Titan) on May 8, 1936! Prior to the approach, the comet's orbit showed it as a very typical centaur:

   Perihelion 1933 Apr 14.300669 +/- 60.1 TT =  7:12:57 (JD 2427176.800669)
Epoch 1935 Jan  1.0 TT = JDT 2427803.5   Sa: 0.0055           Find_Orb
M  15.21976 +/- 1.6
n   0.02428558 +/- 0.000466         Peri.  236.71216 +/- 3.7
a  11.8096487 +/- 0.151             Node    65.92043 +/- 1.4
e   0.2304399 +/- 0.00667           Incl.    2.04309 +/- 0.015
P  40.58                   H 17.2   G  0.15   U  7.7  
q 9.08823334 +/- 0.0386    Q 14.5310640 +/- 0.272
From 93 observations 2002 Mar. 5-2020 Mar. 21; mean residual 0".44

however, after the approach, it quickly turned into a more cometary orbit:

   Perihelion 1944 Apr 20.475679 +/- 0.372 TT = 11:24:58 (JD 2431200.975679)
Epoch 1938 Jan  1.0 TT = JDT 2428899.5   Ju: 0.3745   Sa: 0.0173
M 239.63173 +/- 0.008                                         Find_Orb
n   0.05230047 +/- 4.69e-6          Peri.    8.55626 +/- 0.0055
a   7.08161508 +/- 0.000423         Node   143.22356 +/- 0.0045
e   0.3894235 +/- 4.26e-5           Incl.    5.49170 +/- 0.0008
P  18.85                   H 17.2   G  0.15   U  4.7  
q 4.32386718 +/- 4.31e-5    Q 9.83936298 +/- 0.00089
From 93 observations 2002 Mar. 5-2020 Mar. 21; mean residual 0".44

With Saturn-centric orbital elements on the escape day, one can see that, with a very low chronocentric escape velocity, the comet could have possibly been a temporary satellite of the planet prior to its escape (the exact velocity possibly being slightly lower than indicated here due to unknown non-gravs):

   Perisaturn 1936 May 8.561196 +/- 0.571 TT = 13:28:07 (JD 2428297.061196)
Epoch 1936 May  8.0 TT = JDT 2428296.5                        Find_Orb
q977607.317 +/- 64598               (J2000 equatorial)
                                    Peri.   53.82775 +/- 1.4
                                    Node    33.00363 +/- 0.6
e   1.0978310 +/- 0.00659           Incl.   85.04123 +/- 0.00030
From 93 observations 2002 Mar. 5-2020 Mar. 21; mean residual 0".44

As far as I'm aware, this may be one of the youngest comets in the Solar System, having likely only been showing activity for the past ~76 years, or just 5 perihelion passes since its perturbation. I've heard of quite a few examples of comets interacting with, and sometimes being captured by Jupiter, but I don't believe there are any records of temporary satellite capture by Saturn!

~Sam
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