Asteroid 2017 RS - an extinct comet?

Asteroid 2017 RS was first observed at Pan-STARRS 1, Haleakala on 2017-09-01. 

It is classified as a Mars-crosser.

Its orbit is still very uncertain (condition code 9).

It would be nice to have more data because this asteroid may be an extinct comet.

Orbital data

From JPL Small-Body Database Browser we can see:

(2017 RS)

Classification: Outer Main-belt Asteroid          SPK-ID: 3781340

[ Ephemeris | Orbit Diagram | Orbital Elements | Physical Parameters ]

[ show orbit diagram ]

Orbital Elements at Epoch 2457998.5 (2017-Sep-02.0) TDB Reference: JPL 1 (heliocentric ecliptic J2000)  Element Value Uncertainty (1-sigma)   Units  e .6145637063005263 0.020702 a 4.14837857496493 0.18924 au q 1.598935662796787 0.016606 au i 16.490996995339 0.23653 deg node 221.6460003522266 0.96443 deg peri 165.4311035552846 2.8664 deg M 351.0338219139737 0.34606 deg tp 2458075.363624646766 (2017-Nov-17.86362465) 2.4617 JED period 3086.142680565361 8.45 211.17 0.5782 d yr n .1166504718874665 0.0079819 deg/d Q 6.697821487133073 0.30553 au

Orbit Determination Parameters    # obs. used (total)      18      data-arc span      5 days      first obs. used      2017-09-01      last obs. used      2017-09-06      planetary ephem.      DE431      SB-pert. ephem.      SB431-N16      condition code      9      fit RMS      .20988      data source      ORB      producer      Otto Matic      solution date      2017-Sep-06 18:12:03   Additional Information  Earth MOID = .609695 au   Jupiter MOID = .352027 au   T_jup = 2.605

Simulation in the past 

I used Mercury6 simulator by John Chambers to check what might have happened in the last 10^8 days (about 273000 years).

The arbitrary threshold for the ejection distance is 100 AU.

           Integration parameters
           ----------------------

   Algorithm: Bulirsch-Stoer (conservative systems)

   Integration start epoch:         2458000.5000000 days
   Integration stop  epoch:      -100000000.0000000
   Output interval:                     100.000
   Output precision:                 medium

   Initial timestep:                0.050 days
   Accuracy parameter:              1.0000E-12
   Central mass:                    1.0000E+00 solar masses
   J_2:                              0.0000E+00
   J_4:                              0.0000E+00
   J_6:                              0.0000E+00
   Ejection distance:               1.0000E+02 AU
   Radius of central body:          5.0000E-03 AU

I generated 100 clones with a little R script.

Every orbital parmeter has an average similar to the correspondent nominal one.

Every orbital parameter has a standard deviation equal to the uncertainty shown above.

Result of the simulation for the nominal orbit

These graphs were made using the R ggplot package.

Result of the simulation with 100 clones

After the simulation, I got 78 out of 100 clones that arrived from the outskirt of the solar system.

The actual arrival date range is extremely high: the most recent date was about 1565 AD.

The arrival date distribution is like this (time here is expressed in years):

Kind Regards,

Alessandro Odasso

Extreme TNOs - H mag

Let's apply the same approach described in the previous posts to the TNOs.

I downloaded some days ago a list of 2298 TNOs from the Horizons Web-Interface.

After reading it in an R dataframe, I have plotted the Spearman correlation versus Tisserand parameter with respect to a generic body with ap varying between 20 AU and 1000 AU. Important: I added a filter so to include ONLY asteroids with T <=3 ... this implies that the numerosity of the asteroids is not constant along this plot.

 

After some trials, it seems to me that there is a moderate correlation (better: anti-correlation) for ap = 324 AU (red vertical line).

This is visible in a rough but clear way if you just make a boxplot showing the different H mag distributions in the first and second half of the Tisserand range.

It must be said that the total number of TNOs in this plot is only 45: so I am not sure whether this is significant.

It must also be said that these 45 asteroids are very interesting: among them we can find Sedna and other famous Extreme TNOs that are being studied extensively because their orbits might have been shaped by an unknown massive planet waiting to be discovered.

We can note that the 45 asteroids have a>136 aU and e>0.677

> tapply(z$a,list(z$T324),min)
    FALSE      TRUE
 30.12661 136.09255
> tapply(z$e,list(z$T324),min)
    FALSE      TRUE
0.0000000 0.6776645

Another interesting aspect is described below.

45 TNOs - H Mag depends on Tisserand vs outer planets

Let's calculate the Tisserand parameter Tn with respect to Neptune.

After that we can flag every asteroid TNOs as Tn_le_3 or Tn_gt_3 depending on whether Tn is less than 3 or greater.

Furthermore: we repeat this process for Uranus, Saturn and Jupiter. 

In the end, every asteroid is flagged as follows:

• Neptune:  Tn_le_3 or Tn_gt_3
• Uranus - Tu_le_3 or Tu_gt_3
• Saturn -  Ts_le_3 or Ts_gt_3
• Jupiter - Tj_le_3 or Tj_gt_3

Of course, following the same convention, all our 45 TNOs have T324_le_3: this is how we chose them.

This is the boxplot showing H mag of the 45 TNOs depending on the combination of the above flags:

As you see, something quite peculiar (at least for me!) is going on:

• the brightest TNOs are those who have any Tisserand parameter with respect to outer planets greater than 3.
• when Neptune comes in (I mean: Tn<le_3), the asteroids get darker
• when Neptune and Uranus come in ... the asteroids get darker
• when Neptune, Uranus and Saturn come in ... same as above ... only 1 asteroid.
• when also Jupiter come in ... we find the darkest TNOs of this group of 45 TNOs.

This is something that I can not explain: 

• is this an expected / known result?
• is it a ... statistical fluke?

Cheers,

Alessandro Odasso