<p>The ultimate, perfect answer would be a link to someone's ephemeris file in SPICE kernel format. That's not a realistic hope.</p>
<p>Googling and gnawing, I've found orbital periods, eccentricities, and inclinations for all the Trappist-1 planets, and could calculate positions if I only knew initial conditions, like where each one was in its orbit at any particular epoch.</p>
<p>The Exoplanet Archive has transit prediction tools, which I could use in a pinch to pin down location-time pairs, but is there something that more directly meets the need?</p>
<p>If it matters, the application will be a demo of some software under development which will have a math engine under the hood and an OpenGL visualization of the system on top of that. The relevant decision maker wants to demonstrate accuracy, so &quot;poetic license&quot; about starting positions won't do for this case though it would be the normal demo thing. The system should be able to show actual positions of Trappist-1 planets as a function of time.</p>
<p>For my own education and the benefit of whoever reads this years from now, please include the search terms that brought an answer.</p>

CC BY-SA 4.0
2023-06-09T00:42:20.807Z
SPICE is for targets within our Solar System. I've never heard of it being used for extrasolar systems; new time and spatial reference systems for the extrasolar system along with the 4D spacetime transformations between that system and our ICRF/TDB would need to be defined. I think you're going to need the general equations for turning Keplerian orbital elements into Cartesian state vectors e.g. [here](https://devforum.roblox.com/t/converting-keplerian-orbit-elements-to-cartesian-state-vectors/1705863) (and link under Sources) and $T_c$ of mid-transit in place of $M_0$ as initial condition
astrosnapper
CC BY-SA 4.0
2023-06-12T01:40:33.590Z
Have you read this article: https://ui.adsabs.harvard.edu/abs/2021PSJ.....2....1A/abstract ? I think it might have what you want.
Pierre Paquette
CC BY-SA 4.0
2023-06-13T05:51:27.690Z
That looks promising! Thank you.
An ominous cow word
CC BY-SA 4.0
2023-06-13T05:53:31.103Z
There is also https://www.aanda.org/articles/aa/full_html/2018/05/aa32233-17/T3.html, which lists a mean anomaly for each planet but I'm still looking for where in the paper they give the corresponding epoch.
An ominous cow word
CC BY-SA 4.0
2023-06-13T06:38:35.773Z
@PierrePaquet's reference has a link to something which at first glance looks like what I'm after. That is Table 4 of https://www.aanda.org/articles/aa/pdf/2020/08/aa37392-19.pdf
An ominous cow word
<exoplanet><ephemeris>
How can I find or calculate ephemeris data for the planets in an extrasolar system, specifically Trappist-1?
An ominous cow word
# How can I find or calculate ephemeris data for the planets in an extrasolar system, specifically Trappist-1?

(Asked by: username_0 on 2023-06-09)

The ultimate, perfect answer would be a link to someone's ephemeris file in SPICE kernel format. That's not a realistic hope.

Googling and gnawing, I've found orbital periods, eccentricities, and inclinations for all the Trappist-1 planets, and could calculate positions if I only knew initial conditions, like where each one was in its orbit at any particular epoch.

The Exoplanet Archive has transit prediction tools, which I could use in a pinch to pin down location-time pairs, but is there something that more directly meets the need?

If it matters, the application will be a demo of some software under development which will have a math engine under the hood and an OpenGL visualization of the system on top of that. The relevant decision maker wants to demonstrate accuracy, so "poetic license" about starting positions won't do for this case though it would be the normal demo thing. The system should be able to show actual positions of Trappist-1 planets as a function of time.

For my own education and the benefit of whoever reads this years from now, please include the search terms that brought an answer.

**Tags:** exoplanet, ephemeris

> **Comments:**
> **username_1**: SPICE is for targets within our Solar System. I've never heard of it being used for extrasolar systems; new time and spatial reference systems for the extrasolar system along with the 4D spacetime transformations between that system and our ICRF/TDB would need to be defined. I think you're going to need the general equations for turning Keplerian orbital elements into Cartesian state vectors e.g. [here](https://devforum.roblox.com/t/converting-keplerian-orbit-elements-to-cartesian-state-vectors/1705863) (and link under Sources) and $T_c$ of mid-transit in place of $M_0$ as initial condition  
> **username_2**: Have you read this article: https://ui.adsabs.harvard.edu/abs/2021PSJ.....2....1A/abstract ? I think it might have what you want.  
> **username_0**: That looks promising! Thank you.  
> **username_0**: There is also https://www.aanda.org/articles/aa/full_html/2018/05/aa32233-17/T3.html, which lists a mean anomaly for each planet but I'm still looking for where in the paper they give the corresponding epoch.  
> **username_0**: @PierrePaquet's reference has a link to something which at first glance looks like what I'm after. That is Table 4 of https://www.aanda.org/articles/aa/pdf/2020/08/aa37392-19.pdf  

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## 0 answers

