2012 QF86 and 470805 (2008 VY2)

 Potentially  interesting couple.

Backward simulation performed with Rebound software, all planets + Ceres/Pallas/Vesta

asteroid 2026 JT2 versus comet 83D (1985 epoch)

 refer to this MPML message and related thread.

---------------------------------------------------------------------------
DYNAMICAL ANALYSIS: 5:2 JUPITER RESONANCE
Jupiter Period: 11.862 y | 5:2 Resonant Period: 4.745 y | Center: 2.825 AU
---------------------------------------------------------------------------
Querying NASA JPL SBDB for region 2.8 < a < 2.85 AU...

Successfully retrieved 25387 objects matching the criteria.

--- PROXIMITY ANALYSIS RELATIVE TO Comet 83D (1985) --- TOP 10 RESULTS
0.857 deg | ***        (2026 JT2) ***      | i:23.37 | Node:229.6 | e:0.537
1.239 deg |        (2020 UW24)             | i:23.85 | Node:231.7 | e:0.247
1.270 deg | 478974 (2012 XL103)            | i:23.55 | Node:233.2 | e:0.172
1.298 deg |        (2019 OR58)             | i:21.60 | Node:228.8 | e:0.177
2.065 deg |        (2013 VK45)             | i:24.35 | Node:227.9 | e:0.159
2.574 deg |        (2021 QT100)            | i:20.15 | Node:232.4 | e:0.266
2.790 deg | 587626 (2006 KY60)             | i:19.99 | Node:228.6 | e:0.126
2.922 deg |        (2014 HX537)            | i:20.10 | Node:234.7 | e:0.115
3.039 deg |        (2017 TT19)             | i:20.35 | Node:236.2 | e:0.104
3.114 deg | 625997 (2006 US201)            | i:19.67 | Node:228.4 | e:0.180

this is a zoomed view of the plot:

What if we search for the same objects in the (inc - w) plane?

Here is the resulting plot:

The new plot reveals that the objects that share 83D's (i, Node) plane have totally random perihelion orientations (the scattered blue dots in the attached plot).

2026 JT2 is the only object in the entire 5:2 resonance region (out of ~25,000) to share not just the orbital plane, but the exact ω ~ 0° alignment with 83D (epoch 1985).

(h,k) plane

also zoomed

Here I just searched for the top 10 nearest asteroids to 83D in that plane (again shown as blue dots: they are not the same ones as in the previous plot).

--- TOP 10 CLOSEST OBJECTS IN THE (h, k) PLANE ---

Dist (h,k) | Object Name                    | e      | Varpi(°)

---------------------------------------------------------------------

0.0320     |        (2012 FK62)             | 0.486  | 230.38°

0.0341     |        (2011 OA36)             | 0.488  | 229.17°

0.0484     | ***        (2026 JT2) ***      | 0.537  | 235.99°

0.0526     |        (2022 EQ4)              | 0.538  | 225.98°

0.0652     | 306787 (2001 HS8)              | 0.456  | 228.50°

0.0659     |        (2024 JQ8)              | 0.487  | 224.50°

0.0768     |        (2024 BP23)             | 0.490  | 239.39°

0.0797     |        (2008 KB12)             | 0.569  | 237.59°

0.0933     |        (2024 GY2)              | 0.473  | 240.77°

0.0951     |        (2016 EZ155)            | 0.522  | 241.71°

Asteroid 2026 JT2 is third in the list of the nearest to 83D, the two "intruders" actually being false positives because they do not share their orbital plane.

(p,q) plane

also zoomed:

Here again I just searched for the top 10 nearest asteroids to 83D in that plane (again shown as blue dots).

--- TOP 10 CLOSEST OBJECTS IN THE (p, q) PLANE ---

Dist (p,q) | Object Name                    | i(°)     | Node(°) 

---------------------------------------------------------------------

0.0141     | ***        (2026 JT2) ***      | 23.37°   | 229.62°

0.0200     |        (2020 UW24)             | 23.85°   | 231.71°

0.0213     | 478974 (2012 XL103)            | 23.55°   | 233.15°

0.0216     |        (2019 OR58)             | 21.60°   | 228.85°

0.0341     |        (2013 VK45)             | 24.35°   | 227.87°

0.0420     |        (2021 QT100)            | 20.15°   | 232.42°

0.0457     | 587626 (2006 KY60)             | 19.99°   | 228.60°

0.0483     |        (2014 HX537)            | 20.10°   | 234.72°

Asteroid 2026 JT2 is at the top of the list.

Potential New Fission Cluster?: (23637) 1997 AM6, (580635) 2015 CG73, and 2015 BC618

Orbital data

                             a            e          i         om          w
580635 (2015 CG73)  2.30532288 0.0834925047 7.85348058 101.326491 314.803897
 23637 (1997 AM6)   2.30528533 0.0834721545 7.85472149 101.329196 314.770434
       (2015 BC618) 2.30526674 0.0834717493 7.85456627 101.329981 314.775063

read from JPL Horizons

Orbital similarity
Same-epoch osculating elements (epoch=2461000.5) are extremely similar, and pairwise Drummond (1981) D-criteria are very small:

(23637) 1997 AM6 – (580635) 2015 CG73: D_D ≈ 1.2e-4

(580635) 2015 CG73 – (2015 BC618): D_D ≈ 1.2e-4

(23637) 1997 AM6 – (2015 BC618): D_D ≈ 5.0e-6

Mercury6 backward simulation

)O+_06 Integration parameters  (WARNING: Do not delete this line!!)

) Lines beginning with `)' are ignored.

)---------------------------------------------------------------------

) Important integration parameters:

)---------------------------------------------------------------------

 algorithm (MVS, BS, BS2, RADAU, HYBRID etc) = BS

 start time (days)= 2461221.5

 stop time (days) = -1e8

 output interval (days) = 100

 timestep (days) = 0.05

 accuracy parameter=1.d-12

Backward integration results

Nominal backward integrations taking into account all planets + Ceres + Pallas + Vesta (gravity only; no Yarkovsky) show two distinct pair-like minima:

• (23637) 1997 AM6 – (580635) 2015 CG73: convergence at ~ -46.6 kyr, V_rel ≈ 0.22 m
• (580635) 2015 CG73 – (2015 BC618): convergence at ~ -24.9 kyr, V_rel ≈ 0.18 m/s

 

However, the direct integration of (23637) 1997 AM6– (2015 BC618) does not show a comparable young convergence, finding only a broad higher-velocity minimum near -245 kyr (V_rel ~ 1.5 m/s).

Discussion of origins

two possible interpretations:

 

Scenario 1: Cascade / intermediate parent
(23637) 1997 AM6 splits -> "Object A", which later splits almost in half -> (580635) 2015 CG73 and 2015 BC618.

This matches the nominal timeline (primary event at ~ -46 kyr, secondary event at ~ -25 kyr) and is consistent with the nearly identical H magnitudes of the two smaller bodies.

Difficulty: it is dynamically counterintuitive that (580635) 2015 CG73 is offset from the primary (D_D ~ 1e-4) while 2015 BC618 remains essentially "on top of" the primary (D_D ~ 1e-6). In this scenario, both fragments would be expected to inherit the dispersion/drift of the intermediate parent ("Object A"), so it is not obvious how 2015 BC618 ended up with an osculating orbit so close to (23637) 1997 AM6.

In spite of this, (580635) 2015 CG73 can be traced back to the primary in the nominal integration, while this is not possible for 2015 BC618.

 

Scenario 2: Repeated fission from the primary
(23637) 1997 AM6 ejected both fragments directly in separate events.

This naturally explains why 2015 BC618 matches the primary so closely (it could be a very recent fragment), while the ~ -46 kyr convergence for (23637) 1997 AM6 - (580635) 2015 CG73 would represent a distinct older event.

Difficulties:

(1) it is surprising that the gravity-only integration fails to link (23637) 1997 AM6 and 2015 BC618 at a young epoch

(2) The two small bodies have nearly identical H (and thus may be similar in size if their albedos are comparable) : a curious coincidence for two indipendent ejection events.

 

Conclusion
At present, neither interpretation is fully conclusive.

I would welcome any comments on the dynamical picture.

Are there any physical observations (colors/spectra/albedo/rotation) available for these bodies?

Jupiter Trojans with strict Saturn resonance

For this preliminary analysis, I have utilized current osculating elements. While a definitive dynamical study would require proper elements to account for long-term averages, this high-precision "snapshot" serves as a first step to reveal the instantaneous resonant architecture of the system.I defined two specific cohorts based on the ratio of the asteroid’s orbital period :

$P_{as}$

• Jovian Mode (r1:1): The fundamental frequency of the Jupiter Trojan clouds.

• Saturnian Mode (r5:2): The sub-harmonic frequency associated with the Saturnian "Great Inequality."

An asteroid is "flagged" for a cohort only if it meets a strict relative tolerance:

$$\mid \frac{P_{ast}\mathrm{/}{P}_{planet}}{r}-1\mid <ϵ$$

This filter isolates only the peak of the resonant signal, effectively decoupling the cloud into objects strictly synchronized with Jupiter's frequency and those whose orbits are currently modulated by the Saturnian 5:2 harmonic.

Why this strictness matters
By narrowing the tolerance to 0.001, I am essentially creating a "Dynamical Spectrometer." This isolates only the "peak" of the resonant signal, filtering out the background noise of objects that are merely passing through the neighborhood of a resonance.

This provides the "lens" necessary to decouple the Jupiter Trojan clouds into two distinct populations:

• Objects strictly synchronized with Jupiter's 1:1 frequency ($NumObjects=713)$

  
  

• Objects whose periods are currently aligned with the Saturnian 5:2 frequency ($NumObjects=626$

Structural Analysis: Longitudinal Depletion Zones

Next, I investigated the "texture" of these populations by analyzing the distribution of their longitudes of perihelion 

$\varpi =\omega +\mathrm{\Omega }$

Using an Adaptive Gap-Searching Algorithm, I identified the longitudinal structure of these groups.

Rather than assuming these gaps are permanent "ejection zones," I define them as Longitudinal Depletion Zones—sectors of phase space that are currently under-populated or "forbidden" at this specific epoch.

The algorithm identifies two types of structures:

• Islands (Occupied Sectors): Longitudinal ranges where asteroids cluster together, suggesting pockets of relative stability or "safe harbors."

• Gaps (Depletion Zones): Longitudinal ranges where no asteroids were found in the current census. These likely represent the "porosity" of the gravitational field.

Details

Jupiter Resonace r1_1

   planet resonance            Type     start       end      width n_ast n_com n_total   density threshold
1 Jupiter      r1_1     EMPTY (Gap) -157.4658 -150.6931   6.772678     0     0       0 0.0000000         5
2 Jupiter      r1_1 FILLED (Island) -150.6931 -136.8178  13.875267     0    12      12 0.8648482         5
3 Jupiter      r1_1     EMPTY (Gap) -136.8178 -129.3879   7.429940     0     0       0 0.0000000         5
4 Jupiter      r1_1 FILLED (Island) -129.3879  148.2427 277.630610     0   660     660 2.3772595         5
5 Jupiter      r1_1     EMPTY (Gap)  148.2427  154.4604   6.217691     0     0       0 0.0000000         5
6 Jupiter      r1_1 FILLED (Island)  154.4604  167.2567  12.796277     0    11      11 0.8596250         5
7 Jupiter      r1_1     EMPTY (Gap)  167.2567  172.4148   5.158141     0     0       0 0.0000000         5
8 Jupiter      r1_1 FILLED (Island)  172.4148 -157.4658  30.119396     0    30      30 0.9960359         5

9         5

Saturn Resonace r5_2

  planet resonance            Type     start       end      width n_ast n_com n_total   density threshold
1 Saturn      r5_2     EMPTY (Gap) -153.2552 -146.1287   7.126455     0     0       0 0.0000000     4.166
2 Saturn      r5_2 FILLED (Island) -146.1287 -138.1086   8.020117     0     4       4 0.4987458     4.166
3 Saturn      r5_2     EMPTY (Gap) -138.1086 -133.9423   4.166236     0     0       0 0.0000000     4.166
4 Saturn      r5_2 FILLED (Island) -133.9423 -153.2552 340.687192     0   622     622 1.8257217     4.166

Column meaning:

• Type:

  • FILLED (Island): A longitudinal range where asteroids are "clumping" together. These represent stable pockets where orbits can safely exist.

  • EMPTY (Gap): A "Forbidden Corridor." A longitudinal range where not a single asteroid was found in the current census, indicating a likely unstable or "ejection" zone.

• start / end: The boundaries of the band in degrees, measured in Longitude of Perihelion (

  $\varpi =\omega +\mathrm{\Omega }$

  
  

  • Values are wrapped to the standard 

    $[-{180}^{\circ },{180}^{\circ }]$

     range.

  • Note: If an island's start is a large positive number and end is a large negative number (e.g., 

    ${179}^{\circ }$

    to 

    $-{178}^{\circ }$

    ), it means the island straddles the 180-degree "seam" of the coordinate system.

• width: The angular span of the band in degrees.

  • For Islands, this measures the "Libration Width" (how much an asteroid can wobble and still remain in that specific clump).

  • For Gaps, this measures the size of the "Forbidden Corridor."

• n_ast / n_com: The census count of Asteroid-like (

  $T_j\ge 3.0$

  ) and Comet-like (

  $T_j<3.0$

  ) objects within that specific island. (Naturally, these are 0 for EMPTY rows).

• n_total: The total number of objects in that band (

  $n_{ast}+n_{com}$

  ).

• density: Calculated as 

  $n_{total}\mathrm{/}width$

  . This represents the "Population Packing" of the island.

  • A high density indicates a "Hyper-Stable" core where many asteroids are squeezed into a tiny longitudinal slot.

  • A low density indicates a sparse or "Diffuse" population.

• threshold: The Structural Grain (in degrees) used for the analysis. This is the "chain-breaker" value: any empty space wider than this threshold was officially declared an EMPTY (Gap), splitting the population into separate islands. The threshold is determined by the algorithm: we determine this value by scanning different sizes until we find a Stability Window — a 'elbow' where the number of clusters doesn't change.

Notes:

If this census is correct, there is a disparity in how these two planets "shatter" the Trojan population.

• Jupiter: being the primary host of the 1:1 resonance, Jupiter’s influence is characterized by greater fragmentation. It carves out a higher number of discrete islands separated by broad, "violent" gaps averaging 6.39° in width. This suggests that the local primary mass acts as a broad-spectrum filter, clearing wide swathes of phase space where orbits cannot persist. The primary perturber clears a wider path.
• Saturn: in contrast, the Saturnian 5:2 mode exhibits a much more contiguous and "saturated" structure. It possesses fewer islands and significantly narrower forbidden corridors, averaging  5.65°. This is consistent with it being a secondary perturber.

We are measuring a 1.13 x difference in the "structural grain" of the two modes. While Jupiter sets the global boundaries of the Trojan clouds, Saturn’s harmonic interaction provides a higher-resolution "comb" that allows for a more tightly packed and continuous distribution of objects.

This suggests that the "Maximum Void Width" is a direct indicator of gravitational intensity: the more massive and closer the perturber, the wider the "depletion zones" it creates.

While the fragmentation (number of islands) and porosity (width of gaps) differ between the two modes, both the Jovian 1:1 and Saturnian 5:2 populations are dominated by a single "Mainland" island that hosts the vast majority of the respective asteroids.

When we calculate the midpoint (mean longitude) of these mainland islands, the result is as follows:

• Jupiter r1_1 Mainland (N=660/713 --> 92%):
• Span: -129.39° to 148.24°
• Midpoint: ~9.4°
• Saturn r5_2 Mainland (N=622/626 -->99%):
• Span: -133.94° to -153.25° (wrapping around the 180° seam)
• Midpoint: ~36.4

The current Longitude of Perihelion for Jupiter is approximately 15.0°.

The current Longitude of Perihelion for Saturn is approximately 92.0°.

Midpoint Alignment

$\mathrm{<span\; style="font-family:\; courier;">\varpi </span>}$

• The Jovian Mainland midpoint (~9.4°) being relatively near Jupiter’s own perihelion (15.0°) is exactly what celestial mechanics predicts. Most Trojans have their perihelia "locked" or oscillating around Jupiter's perihelion to maintain secular stability.

• The Saturnian Mainland midpoint (~36.4°) is fascinating. It suggests that objects most sensitive to the Saturn 5:2 resonance are shifted roughly 20-25° away from the Jovian average towards the Saturn perihelium. These asteroids are "tilting" their orbits to find a gravitational equilibrium between the two giants.

The "Anti-Alignment" Void

There is a striking correlation in the location of the Gaps:

• Jupiter Gap 1: -157.4° to -150.6°

• Saturn Gap 1: -153.2° to -146.1°

These two gaps almost perfectly overlap. The midpoint of these gaps is roughly -152°
Jupiter's perihelion is at 15°. The "Anti-perihelion" (aphelion direction) is -165°.
There is an Instability Corridor near the anti-alignment of Jupiter’s orbit. Asteroids whose perihelia drift into this sector likely experience a "kick" that pushes them out.

 

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