174P/Echeclus

60558 Echeclus (2000 EC98) also known as 174P/Echeclus is a centaur that occasionally shows a cometary activity.

Outbursts happened in 2005, 2011 and in the first days of December 2017 (see MPML message from Brian Skiff) and confirmation from Richard Miles and Jean-François Soulier.

The 2017 outburst is the strongest ever witnessed.

I simulated 100 clones of this centaur in the past 10^8 days trying to confirm its possible cometary origin: note that I am not taking into account the non gravitational forces associated to its outburst, not clear to me if they have a considerable effect.

The first step was to generate clones having orbital parameters distributed around the nominal ones with 1-sigma uncertainty as follows:

JPL Small-Body Database Browser

60558 Echeclus (2000 EC98)

Classification: Centaur          SPK-ID: 2060558

[ Ephemeris | Orbit Diagram | Orbital Elements | Physical Parameters | Discovery Circumstances | Close-Approach Data ]

[ show orbit diagram ]

Orbital Elements at Epoch 2458000.5 (2017-Sep-04.0) TDB Reference: JPL 85 (heliocentric ecliptic J2000)  Element Value Uncertainty (1-sigma)   Units  e .4556668817376728 1.2005e-07 a 10.68172886788859 2.2774e-06 au q 5.814418783090517 4.1275e-07 au i 4.344445692331014 6.4394e-06 deg node 173.3332131350017 5.505e-05 deg peri 162.8042218299513 5.7268e-05 deg M 24.47205469604485 6.4974e-06 deg tp 2457133.680473384613 (2015-Apr-21.18047338) 0.00022632 JED period 12751.48464064088 34.91 0.004078 1.116e-05 d yr n .02823200671493785 9.0289e-09 deg/d Q 15.54903895268667 3.3152e-06 au

Orbit Determination Parameters    # obs. used (total)      2888      data-arc span      13948 days (38.19 yr)      first obs. used      1979-09-23      last obs. used      2017-11-30      planetary ephem.      DE431      SB-pert. ephem.      SB431-N16      condition code      0      fit RMS      .44363      data source      ORB      producer      Otto Matic      solution date      2017-Dec-07 16:00:47   Additional Information  Earth MOID = 4.80483 au   Jupiter MOID = .838614 au   T_jup = 3.031

Simulation approach

Mercury6 Integrator

reference:

J.E.Chambers (1999) 

A Hybrid Symplectic Integrator that Permits Close Encounters between Massive Bodies''. Monthly Notices of the Royal Astronomical Society, vol 304, pp793-799.

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

   Algorithm: Bulirsch-Stoer (general)

   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


Simulation Results

• 77 out of 100 clones have a cometary orbit (i.e. they came from a distance greater than 100 AU).

• of which: 3 came on a hyperbolic orbit. The one that had the highest speed had a Vinfinity about 3.7 km/s (Vinfinity = 42.1219*sqrt(-0.5/a) --> the semi-major axis being about -63.6 AU

The time (Year) when they entered the solar system was distributed as follows:

   Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
-272080 -109330  -62183  -82802  -36357   -4980

In a graphical form:

A look at the nominal asteroid
The nominal asteroid itself has a cometary origin.

It entered into the solar system at about year -105000 B.C.

In the plot below, the dashed vertical lines correspond to a close approach with Jupiter.

Note that Jupiter was not immediately important. 

In its early history, 174P/Echeclus was much more influenced by Saturn as shown here:

Coming back to plots showing the role of Jupiter, we can see these other ones:

A look at the clones - "footprint" diagrams

At any given time in the past, a clone had a certain perihelium q and a certain aphelium Q (I disregard the clones when on an hyperbolic trajectory because Q would be infinite).

Let's imagine that we plot all possible q-Q points in a diagram: the highest density area is the one where the clones happened to be for most of the time.

This is shown here ( I have used the R function stat_density2d - color scale implemented by viridis library):

Analysis of close approaches
These plots show the distribution of close appproaches (number and Dmin distance) between the clones and the major planets.

Kind Regards,
Alessandro Odasso

Amor 2002 RN38

This NEO is listed in the page of Asteroids with Comet-Like Orbits maintained by Y. Fernandez.

It was also discussed as an object with a likely cometary origin in some papers, among which I found:

• "On Near-Earth Asteroid Study at Department of  Astronomy, Bandung Institute of Technology" by S. Siregar.
• "Assessing the physical nature of near-Earth asteroids through their dynamical histories" by Julio A. Fernández, Andrea Sosa, Tabaré Gallardo, Jorge N. Gutiérrez.

At the time I made this analysis, this Amor was last observed on November 11th, 2017 and the orbit uncertainty is 0 being based on 119 observations acquired in the last 15 years.

JPL Small-Body Database Browser:

Orbital Elements at Epoch 2458000.5 (2017-Sep-04.0) TDB
Reference: JPL 31 (heliocentric ecliptic J2000)

Element Value Uncertainty (1-sigma)   Units  e .6730769823381273 2.1793e-07 a 3.820825408551513 1.2346e-07 au q 1.249115772522818 7.9678e-07 au i 4.160437503290696 1.756e-05 deg node 296.1904517164833 0.00024613 deg peri 118.6156866423836 0.00026072 deg M 357.1006606538095 3.1062e-05 deg tp 2458022.470035828635 (2017-Sep-25.97003583) 0.00023642 JED period 2727.936248200967 7.47 0.00013222 3.62e-07 d yr n .1319678933983206 6.3964e-09 deg/d Q 6.392535044580208 2.0656e-07 au

Orbit Determination Parameters    # obs. used (total)      119      data-arc span      5568 days (15.24 yr)      first obs. used      2002-08-18      last obs. used      2017-11-15      planetary ephem.      DE431      SB-pert. ephem.      SB431-N16      condition code      0      fit RMS      .55328      data source      ORB      producer      Otto Matic      solution date      2017-Nov-16 07:18:58   Additional Information  Earth MOID = .270556 au   Jupiter MOID = .260678 au   T_jup = 2.626

I simulated 100 clones of this asteroid in the past 10^8 days trying to confirm its possible cometary origin: the goal is to determine whether some clones might have arrived from the outskirt of the solar system - arbitrary threshold: 100 AU.

Simulation approach

Mercury6 Integrator

reference:

J.E.Chambers (1999) 

A Hybrid Symplectic Integrator that Permits Close Encounters between Massive Bodies''. Monthly Notices of the Royal Astronomical Society, vol 304, pp793-799.

           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


Simulation Results

• 79 out of 100 clones have a cometary like orbit.
• of which: 13 came on a hyperbolic orbit (Vinfinity = 42.1219*sqrt(-0.5/a) --> the minimum absolute value for semi-major axis a was -17.46 AU -->the maximum value for Vinfinity was 7.14 km/s 
• 1 out of 100 was discarded because "hit" the sun (due to extremely high eccentricity).

The time when they entered the solar system was distributed as follows:

   Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
-272319 -151956  -85380 -100222  -38660    -370

In a graphical form:

The most recent arrival in the solar system could have happened a relatively short time ago compared to other asteroids with a cometary like orbit: year 370 B.C.

A look at the nominal asteroid

The nominal asteroid is one of the 79 clones with a cometary like orbit. It apparently arrived in the solar system about in year 87000 B.C 

In the following plots (made with R package ggplot2), the vertical dashed lines show a close encounter with Jupiter.

Close Approaches analysis
For every given planet, every clone had a certain number of close approaches so we can calculate the mean number of close approaches and the mean number of Dmin (distance of the close approach). Even better, we can print a boxplot showing the distribution of the number of close approaches and their distances.

Kind Regards,
Alessandro Odasso

asteroid 2016 WU9 vs comet 3D/Biela

Comet 3D/Biela was a Jupiter Family comet discovered in 1772 by Montaigne and, independentely, by Messier. 

It was identified as periodic in 1826 by Wilhelm Van Biela (period 6.6 years).

In the following decades, the comet disintegrated and in 1872, quoting Wikipedia , "...a brilliant meteor shower (3,000 per hour) was observed radiating from the part of the sky where the comet had been predicted to cross in September 1872. This was the date when Earth intersected the comet's trajectory. These meteors became known as the Andromedids or "Bielids" and it seems apparent that they were produced by the breakup of the comet. The meteors were seen again on subsequent occasions for the rest of the 19th century, but have now faded away, probably due to gravitational disruption of the main filaments".

Looking at JPL Small-Body Database Browser, it seems that the current Apollo asteroid 2016 WU9 orbit bears some resemblance with the orbit of comet 3D/Biela (orbital element estimated at epoch 1832-Dec-03.0).

3D/Biela

Classification: Jupiter-family Comet [NEO]          SPK-ID: 1000504

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

[ show orbit diagram ]

alternate orbits:

Orbital Elements at Epoch 2390520.5 (1832-Dec-03.0) TDB Reference: IAUCAT03 (heliocentric ecliptic J2000)  Element Value Uncertainty (1-sigma)   Units  e 0.751299 n/a a 3.53465808340135 n/a au q 0.879073 n/a au i 13.2164 n/a deg node 250.669 n/a deg peri 221.6588 n/a deg M .9469569963959761 n/a deg tp 2390514.115200000000 (1832-Nov-26.61520000) n/a JED period 2427.278122182916 6.65 n/a n/a d yr n .1483142770949718 n/a deg/d Q 6.190243166802708 n/a au Additional Model Parameters  Parameter Value Uncertainty (1-sigma)  A1 [SET] 0.39E-8 n/a A2 [SET] -0.0254E-8 n/a		Orbit Determination Parameters    # obs. used (total)      26      planetary ephem.      DE405      data source      ORB      producer      Marsden   Additional Information  Earth MOID = .000518224 au   T_jup = 2.531

(2016 WU9)

Classification: Apollo [NEO]          SPK-ID: 3764861

[ Ephemeris | Orbit Diagram | Orbital Elements | Physical Parameters | Close-Approach Data ]

[ show orbit diagram ]

Orbital Elements at Epoch 2457719.5 (2016-Nov-27.0) TDB Reference: JPL 3 (heliocentric ecliptic J2000)  Element Value Uncertainty (1-sigma)   Units  e .7580579821266318 0.0032624 a 3.542266282670314 0.046712 au q .8570230522740508 0.00025535 au i 11.74490053832628 0.036722 deg node 243.8119317636647 0.0028055 deg peri 238.6437633713563 0.0047637 deg M 354.0963591324415 0.12305 deg tp 2457759.433526534912 (2017-Jan-05.93352654) 0.042468 JED period 2435.119255232367 6.67 48.168 0.1319 d yr n .1478367021354146 0.0029243 deg/d Q 6.227509513066578 0.082122 au

Orbit Determination Parameters    # obs. used (total)      14      data-arc span      5 days      first obs. used      2016-11-26      last obs. used      2016-12-01      planetary ephem.      DE431      SB-pert. ephem.      SB431-N16      condition code      8      fit RMS      .57283      data source      ORB      producer      Otto Matic      solution date      2017-Apr-06 08:21:48   Additional Information  Earth MOID = .0396698 au   Jupiter MOID = .640753 au   T_jup = 2.523

One can wonder whether asteroid 2016 WU9 is a remnant of comet 3D/Biela.

In order to answer, it would be important to be able to model the effect of non gravitational forces.

I am unable to do that but I show you the result of a simulation done with Mercury6 taking into account only gravitational forces.

Simulation set-up

Mercury6 Integrator

reference:

J.E.Chambers (1999) 

A Hybrid Symplectic Integrator that Permits Close Encounters between Massive Bodies''. Monthly Notices of the Royal Astronomical Society, vol 304, pp793-799.

           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

In order to perform the simulation I generated 100 clones of asteroid 2016 WU9 (same average orbital parameters as the nominal ones and standard deviation almost about the one calculated by JPL).

I also simulated the behavior of nominal comet 3D/Biela for which I do not find the uncertainty estimates.

Thus, I evaluated 100 couples with an R script to check whether there was a moment in the past when two clones were very near to comet 3D/Biela with a very low relative velocity.

Simulation Results
First, you see a graph showing the relative distance between 2016 WU9 clones and come 3D/Biela (some outliers not shown).
Second, the correspondent graph for relative velocities.

At first glance nothing impressive but around January 1806, one clone and nominal comet D/Biela were separated by a distance of about 10 LD (i.e.  0.025 AU) with a relative velocity 0.0030 AU/Day.
For comparison: I read that in 1852  two fragments comet A and comet B were observed and their distance was estimated to be about 2.5 million km (i.e 6 LD).
In conclusion:

• for a few clones, the order of magnitude of the distance may be compatible with 2016 WU9 being a fragment of the comet.

Not clear to me if this is just a coincidence or there could be more.

2016 WU9 - a possible cometary origin
While the relation between asteroid 2016 WU9 and comet 3D/Biela remains highly speculative, I think it is interesting to note a second result of the simulation of asteroid 2016 WU9: this Apollo asteroid seems to move on an unstable orbit, it might have a cometary origin itself (whether or not it is related to comet 3D/Biela).

Of course, the uncertainty is very high, but, at least, this result is consistent with the fact that asteroid 2006 WU9 appears in the  Asteroids with Comet-Like Orbits: Elements and Positions by Fernandez.
This is what I got (graph done with package ggplot2):

• 68 out of 100 clones arrived in the solar system from a distance greater than 100 AU
• 4 out of 100 clones "hit" the sun (considering that the integration was backword, this means that they seem to have originated from the sun - not clear if this is a simulation glitch or a "normal" result that happens when the eccentricity gets almost 1)

Arrival Time distribution

Year of clone arrival time :

     Min.   1st Qu.    Median      Mean   3rd Qu.      Max.
-271250.0 -158468.8  -79389.5 -103213.8  -40550.2     -32.0  

In a graphical form:

Every clone has its own story, no reason to choose a specific one.
Just to have a feeling of a possible macroscopic behaviour (the dotte lines correspond to a close encounter with Jupiter):

Kind Regards,
Alessandro Odasso