Amateur discovery of a new moon of Jupiter


kly
 

Hi all,

I'm that amateur astronomer who recovered four of Jupiter's lost moons back in December 2020.

Lately I've been working on a rudimentary project to revisit a comprehensive Jovian moons survey by Jewitt, Sheppard and Gladman et al. in 2003, which for some reason was largely undocumented despite its fruitful result of 23 Jovian moon discoveries. For a full-scale survey of Jupiter's Hill sphere like this, the data is very much unexplored when you consider that many of the recently-discovered moons (i.e. Ersa and Valetudo) were present and clearly visible in this dataset but were not reported hitherto (I've already submitted 2003 precovery observations of the 2016–2018 moons to the MPC). To supplement this, I've created a crude map showing the positions of all known Jovian moons discovered after 1999 and the February 2003 CFHT images they appear in: https://imgur.com/a/jdTfH1p 

I decided to begin my search in a set of Feb 24 CFHT images situated eastward nearest to Jupiter (691381p, 85p, and 91p), which I expected to harbor a variety of inner progrades and outer retrogrades that may have been lost and unreported due to Jupiter's glare. I've manually checked 19 out of 36 CCDs so far and I've managed to find three unidentified moon candidates (motions within 13"–21"/hr, not listed in MPC's Natural Satellites Ephemeris Service), two of which were unrecoverable either due to their faintness or were obstructed by CCD gaps in subsequent observations. My third candidate, which I've temporarily designated 'EJc0061', happened to be present in CFHT observations on Feb 25-27 and earlier Subaru observations on Feb 05-06, establishing a 22-day arc that effectively confirms that the object is bound to Jupiter (U=10.4).

I was then able to track this moon down in later CFHT observations from Mar 12 and Apr 30. Although both images had rather mediocre seeing due to Jupiter's glare, the moon's 1-sigma ephemeris uncertainty was stringent enough (<10") for me to confidently identify it. From there on, the orbit and ephemeris quality was decent enough for me to begin searching observations beyond 2003: I found it in Subaru observations from 2005 Mar 11 (1' off its predicted position!), CFHT observations from 2010 Oct 02-30, and finally CTIO/DECam images from 2017 Mar 23-26, 2018 Apr 12-13, and May 11-12. There were no viable precovery observations of this moon, as it happened to be masked behind CCD artifacts in CFHT observations from 2001 Dec 10. For those interested, I've compiled a gallery of CFHT images of this moon at https://imgur.com/a/RW1UehA.

In the end, I measured a total of 76 observations spanning an arc of 15.26 years (5,575 days). The orbit of this Jovian moon is now well-secured for decades to come, so I hereby present to you: Jupiter's 80th moon, EJc0061 = S/2003 J 24 (provisional designation pending)!

   Perijove 2021 Jan 19.320884 +/- 0.0161 TT =  7:42:04 (JD 2459233.820884)
Epoch 2021 Jul  5.0 TT = JDT 2459400.5                        Find_Orb
M  86.48445599 +/- 0.008            (J2000 ecliptic)
n   0.51886797 +/- 1.24e-6          Peri.  169.25127 +/- 0.006
a   0.15102114 +/- 2.42e-7          Node   289.08642 +/- 0.0023
e   0.1681198 +/- 7.09e-6           Incl.  163.42428 +/- 0.0010
P   1.90/693.81d           H 16.4   G  0.15   U  3.8  
q 0.12563148 +/- 9.75e-7    Q 0.17641079 +/- 1.25e-6
From 76 observations 2003 Feb. 5-2018 May 12; mean residual 0".16

Residuals in arcseconds: 
030205 568  .00   .13-    101002 568  .05-  .04+    180412 W84  .04+  .05-    
030205 568  .29-  .06+    101002 568  .08-  .24-    180413 W84  .05+  .14-    
030206 568  .13-  .14-    101009 568  .03-  .08-    180413 W84  .17+  .18-    
030206 568  .07-  .07-    101009 568  .02+  .09-    180413 W84  .08+  .06-    
030206 568  .15-  .04+    101009 568  .04+  .11-    180511 W84  .01+  .28+    
030224 568  .06-  .01-    101009 568  .08-  .13-    180511 W84  .14-  .24+    
030224 568  .18-  .04+    101009 568  .06-  .15-    180511 W84  .01+  .11+    
030224 568  .01-  .05-    101030 568  .11-  .01-    180511 W84  .05-  .12+    
030225 568  .11-  .19+    101030 568  .04-  .21-    180511 W84  .07-  .38+    
030225 568  .13+  .37+    101030 568  .18+  .10-    180511 W84  .12+  .25+    
030225 568  .01-  .23+    170323 W84  .06-  .01+    180511 W84  .01-  .11+    
030227 568  .18-  .04+    170323 W84  .07-  .01-    180511 W84  .01-  .27+    
030227 568  .15-  .15-    170324 W84  .11-  .05+    180511 W84  .14-  .03+    
030227 568  .27-  .15-    170324 W84  .03+  .32-    180511 W84  .24-  .02-    
030312 568  .11-  .02+    170324 W84  .13-  .25+    180512 W84  .10-  .10+    
030312 568  .13-  .21+    170326 W84  .03+  .16-    180512 W84  .20-  .09+    
030312 568  .01-  .31+    170326 W84  .18+  .12-    180512 W84  .16-  .09+    
030430 568  .68+  .11+    170326 W84  .02+  .24+    180512 W84  .12-  .18+    
030430 568  .48+  .04+    170326 W84  .00   .03-    180512 W84  .23-  .08+    
030430 568  .42+  .17-    170326 W84  .02-  .18-    180512 W84  .25-  .03+    
050311 568  .12-  .12-    170326 W84  .04-  .04-    180512 W84  .22-  .03+    
050311 568  .06-  .12-    170326 W84  .06-  .02-    180512 W84  .17-  .12+    
050311 568  .10+  .05+    170326 W84  .07+  .02+    180512 W84  .13-  .22+    
101002 568  .08-  .08+    170326 W84  .05+  .06+    180512 W84  .21+  .08+    
101002 568  .12-  .10+    180412 W84  .19+  .07-    
101002 568  .16-  .12+    180412 W84  .18+  .11-    

I'm proud to say that this is the first planetary moon discovered by an amateur astronomer! Other than that, there really isn't anything remarkable about this Jovian moon—it's just a typical member of the retrograde Carme group. Its Rmag range of 23.2–23.5 falls just below Ashton et al.'s proposed completion limit of Rmag=23.2 for known retrograde Jovian moons.

As of writing this, the Minor Planet Center has not published my astrometry yet. For this reason, I shall withhold my astrometry unless obliged privately. In the meantime, I will continue my hunt for unidentified Jovian moons in the February 2003 dataset, so stay tuned for additional Jovian moon discoveries by me in the next coming months! (and I'd highly appreciate some help from professionals who are willing to share their proprietary astrometry of Jovian moon candidates from the 2003 survey.)

Lastly, I thank my friends Sam Deen, Elvis Mendes, Andy Roberts, and Dreigorich for sticking with me during the entire process of discovering this moon. Furthermore, I also thank Stephen Gwyn et al. for the CADC's SSOIS, Pierre Fernique for Aladin Sky Atlas, and Bill Gray for Find_Orb. This discovery would not have been possible without their tools.

Kai (they/them)

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