N-Body Simulations of two Dynamically New Comets with different compositional characteristics

Comets are primitive small bodies that are mainly distributed in two big reservoirs, i.e., the Kuiper Belt and the Oort Cloud. The Oort Cloud is the source of the Long-Period Comets, hereafter LPCs, having isotropic inclinations. Dynamically New Comets, hereafter DNCs, are a subset of the LPCs having the semi-major axis greater than 10000 au [1]. These comets are called new because they have never been to the inner solar system before. Understanding these comets can give us insights into the evolution of the early solar system.  The origin of the DNCs, is still an open question.

In this work, we compare two DNCs, coming into the inner solar system for the very first time. Comet C/2020 V2 (ZTF), hereafter comet V2, had a perihelion distance of 2.28 au (8th-May-2023), while comet C/2023 A3 (Tsuchinshan-ATLAS), hereafter comet A3, had a perihelion distance of 0.39 au (27th-Sept-2024). On comparing the molecular band production rate ratios using spectroscopic and photometric techniques,  comet V2 is found to be typical in carbon composition (Ahuja et al., in preparation), while comet C/2023 A3 (Tsuchinshan-ATLAS), hereafter comet A3, is found to be depleted in carbon composition (Atel #16637, [2]). 

Both comets, V2 and A3, are in hyperbolic orbits as mentioned on the NASA JPL Horizons webpage.  Comet V2 has a heliocentric eccentricity of 1.000949 with an uncertainty of 0.0000027 or at almost 352σ level at the solution date of 28 Aug 2022, and comet A3, at the solution date of 01 Mar 2024, has a heliocentric eccentricity of 1.00012 with an uncertainty of 0.0000004 or at almost 300σ level. This shows that the comets are, presently (post-perihelion), in an unbound orbit. To understand these comets’ past and future, we have used the REBOUND simulation package [3] and run the simulation in the past and future for 1 million years. This is done to see whether the comets were bounded or unbounded prior to this perihelion passage.  To predict the nature of the orbit from this numerical simulation, we have used statistical methods and created 1000 clones by applying a multivariate distribution using the covariance matrix provided by the NASA JPL Small Body Database (SBDB) [4]. We have dynamically evolved these massless clones in the past and future, and then calculated the velocity parameter, which is the difference between the barycentric velocity calculated 1 million years ago and the escape velocity, which is calculated at the distance the clones reached at that time. The variation of the velocity parameter is used to calculate the probability of the comet being bound to the solar system or the comet being an interstellar interloper in the past.

Figure 1:  Distribution of radial distance (in au) vs time (in million years) for 200 massless clones of comet V2 integrated backwards to 1 million years. 

Figure 2: Distribution of radial distance (in au) vs time (in million years) for 200 massless clones of comet A3 integrated backwards to 1 million years. 

 

In Figure 1, we have plotted the radial distance vs time for the 200 massless clones of comet V2, integrated backwards for 1 million years. As shown in the figure, there is no interaction of comet V2 with the planets prior to the current apparition. We have also calculated the radial velocity of the comet V2  and used it to calculate the velocity parameter. The velocity parameter is the difference between the barycentric velocity and escape velocity in units of escape velocity. The distribution of the velocity parameter is between -0.48 to -0.41, which shows that the comet is bounded.

Similarly, Figure 2 shows the radial distance vs time for the 200 massless clones of comet A3 integrated backwards for 1 million years.  The velocity parameter is found to be -0.17 to -0.12, which also shows comet A3 to be bound to the solar system in the past.  

From our simulations, we conclude that the comets V2 and A3, now in hyperbolic orbits, were bound to the solar system in the past.

 

Acknowledgement:

We acknowledge the local staff at the Mount Abu InfraRed Observatory for their help. We thank the staff of Indian Astronomical Observatory, Hanle and Centre For Research & Education in Science & Technology, Hoskote that made these observations possible. The facilities at IAO and CREST are operated by the Indian Institute of Astrophysics, Bangalore. Work at Physical Research Laboratory is supported by the Department of Space, Govt. of India.

This work is a result of the bilateral Belgo-Indian projects on Precision Astronomical Spectroscopy for Stellar and Solar system bodies, BIPASS, funded by the Belgian Federal Science Policy Office (BELSPO, Government of Belgium; BL/33/IN22_BIPASS) and the International Division, Department of Science and Technology, (DST, Government of India; DST/INT/BELG/P-01/2021(G)).

 

References:

[1] Completing the Inventory of the Solar System, Levison H. F., 1996,  Astronomical Society of the Pacific Conference Proceedings, 107, 173.

[2] Molecular gas production rates of Comet C/2023 A3 (Tsuchinshan-ATLAS)., Ahuja, G., Aravind, K., Sahu, D., Jehin, E., Donckt, M.V., Hmiddouch, S., Ganesh, S., Sivarani, T., 2024. In: The Astronomer’s Telegram. p. 16637.

[3] REBOUND: an open-source multi-purpose N-body code for collisional dynamics, H.  Rein, S.-F.  Liu, A&A 537 A128 (2012), DOI: 10.1051/0004-6361/201118085

[4] Spectroscopic and dynamical properties of comet C/2018 F4, likely a true average former member of the Oort cloud, J.  Licandro, C.  de la Fuente Marcos, R.  de la Fuente Marcos, J.  de León, M.  Serra-Ricart, A.  Cabrera-Lavers, A&A 625 A133 (2019), DOI: 10.1051/0004-6361/201834902