# I have a question about the wording in a paper about a planetary system and comets

I was reading a paper. This is the paper: https://arxiv.org/abs/2006.01711 (https://ui.adsabs.harvard.edu/abs/2020MNRAS.496.4979D/abstract

In the method section in the second paragraph there is a bit of wording that is confusing to me.

We will examine the dynamics of some Solar System comet analogs3, namely, 2P / Encke, 9P / Tempel 1, and 31P / Schwassmann-Wachmann 2; they are later referred to as comet A, B, and C, respectively, for convenience.

The paper is essentially about a system called 55 cancri. They do simulations about it to look at comet interaction since there is an empty space without planets where there might be comets. They say they examine 3 solar system comets. Does that mean they just use the regular 3 planets and star in the 55 cancri system and then add 3 comets as an assumption? Or do they do 2 different simulations one for the solar system to test the numerical simulation and then the cancri system?

The confusion also arises since they mention comet analogs. I do not understand what analog means here. They also link to a table with the planets in the 55 cancri system which I do not understand how it relates to this sentence.

Can somebody explain what they mean here?

What they have done is take each of the 580 Jupiter-Family Comets (JFCs) from our solar system (from the JPL Small Body DataBase; set object kind=comets, Comet Orbit Classes to Jupiter-family Comet) and kept all of the orbital elements the same, except for the semi-major axis which they have scaled by the ratio of the semi-major axis 55 Cnc d (5.74 au) to Jupiter's (5.2 au). So a comet with a semi-major axis of 3 au in our solar system would be $$3\times(5.74/5.2)=3.312\,au$$ in the 55 Cnc system - this is what they are referring to as comet analogs

All of these 580 comet analogs are being inserted into the 55 Cnc system, For each comet analog inserted, they are creating 100 clones of each analog, varying the mean anomaly. This creates almost 60,000 "comets" which are then integrated along with the 55 Cnc system planets and the outcomes of the comet clones are tracked to see how many survive, how many are ejected from the 55 Cnc and over what timeframe. To illustrate this, they have picked the 3 comet analogs of 2P/Encke, 9P/Tempel 1 and 31P/Schwassmann-Wachmann 2 as examples of JFCs which have high, medium and low eccentricity respectively (their Table 2) and find that comets which have eccentricity tend to preferentially ejected and in a shorter time due to a greater number of encounters with the planets of the 55 Cnc. This occurs much quicker in the 55 Cnc system than their corresponding counterparts in our Solar System.

• Thank you so much. It makes so much more sense now. Apr 16 '21 at 8:13
• @astroWolf it's totally up to you, but if you feel that this completely answers your question you can click the "accept" check mark next to this answer.
– uhoh
Apr 21 '21 at 21:23