Asteroid Ephemerides / New XEPH Files - 2022 Release

Juan Conejero

Juan Conejero

PixInsight Staff
Staff member
A new set of asteroid ephemerides files in XEPH format is now available on our distribution server. The new files cover the time span from 2019-12-02 to 2023-01-01 and include the first 500,000 numbered asteroids. These XEPH files can be used to compute high-precision ephemerides with our solar system ephemerides engine, as well as to generate asteroid annotations for plate-solved images with our standard AnnotateImage script.

The new XEPH files provide Chebyshev polynomial expansions for position in barycentric rectangular coordinates coherent with fundamental JPL DE440 ephemerides (ICRS), with maximum truncation errors below 1e–10 au (about 15 meters) for the vast majority of objects in the main asteroid belt, and proportionally smaller errors for objects closer to the Sun.

These XEPH files have been generated by numerical integration of perturbed orbital motion with our standard EphemerisGenerator process. Initial conditions have been obtained from the Asteroid Orbital Elements Database by Lowell Observatory, latest astorb.dat file for epoch 2022-01-21. The implemented physical model includes:
  • Perturbations from Mercury, Venus, Earth, Moon, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. State vectors and constants are provided by XEPH fundamental ephemerides (currently JPL's DE440).

  • Perturbations from the 343 most massive asteroids used in DE430 and DE440 numerical integrations. State vectors and constants are provided by XEPH asteroid ephemerides (currently DE430 asteroid ephemerides consistent with DE440).

  • Perturbations from the 30 most massive Kuiper belt objects (KBOs). State vectors and constants are provided by XEPH ephemerides generated with this same implementation, starting from DE440 initial state vectors.

  • Relativistic perturbation terms (DE440's PPN model) up to O(1/c^2) for the point-mass accelerations induced by all planets, Moon, Pluto and the five most massive asteroids.

  • Direct acceleration perturbation terms caused by oblateness. Zonal harmonics J2 are computed for Sun, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Please note that these files don't include the 343 most massive asteroids, which are already available directly on the PixInsight platform for a much larger time span (from 1550 to 2650) from DE430/DE440 ephemerides. So if you are going to generate asteroid annotations, don't forget to include an Asteroids annotation layer besides custom XEPH layers.

The whole numerical integration to generate these 10 XEPH files (826 MiB) has required about 75 hours on a dedicated workstation with an AMD Ryzen 9 5950X 16-core processor and 128 GiB of RAM running Kubuntu 20.04 Linux.
 
It appears that these files do not contain the Dwarf Planets such as 136199 Eris, 136108 Haumea, 136472 Makemake, 120347 Salacia and others. These minor planets are also not included in either the Planet or the most massive asteroid files either. Where are these located so that you can generate Ephemerides or be used in AnnotateImage scripts?

Rod
 
Hi Rod,

All of these big trans-neptunian objects are included in the platform KBO ephemerides file, which is available at the following installation directory:

PixInsight/rsc/eph/core-kbo.xeph

These objects are part of the set of 30 largest known KBOs used as perturbers for generation of the asteroid ephemerides files, so they are not included in these files because they cannot be part of the numerical integration (an object cannot perturb its own orbit).
 
Great. Since the KBO ephemerides file is not a pick choice as a Layer Class in the AnnotateImage script do to you have to add it as a custom xeph file?

Rod
 
Yes, as a custom XEPH file. I'll add a specific layer for KBOs to the AnnotateImage script in the next version.
 
Thank you Juan. As you know, I created a YT video that highlights this capability.
Just so I understand...I do need to load multiple Custom XEPH files populate (now)10 slots correct?
I can't think reason someone would only choose a subset of these. Is there a way to concatenate the files and load as a single thing? (or load all of them in one go?)

-adam
 
Hi Adam,

Yes, I've seen your YouTube video and it's very nice, thank you so much for documenting this important functionality.

Yes, you need 4 custom XEPH layers to load the 10 files. I know that the current system of custom XEPH layers in AnnotateImage is tedious, and even more now because we have 10 files, which means at least 30 mouse clicks! :rolleyes: I'll rewrite this functionality to allow you select a set of files in a single operation, so multiple layers won't be necessary.
 
By the way, I forgot to mention something very important. To generate accurate asteroid annotations you should compute astrometric solutions with distortion corrections enabled (thin plate splines). Of course, the Gaia EDR3 catalog (through local XPSD files) and accurate geodetic coordinates and acquisition times are also absolutely necessary.
 
they are in the distribution server, where you download the core application. by default the section is collapsed so you might have missed it. it is right above the actual pixinsight package files on the page.

rob
 
It appears this script has changes with respect to the asteroid XEPH files and usage.
Was there an announcement concerning this change? How is it utilized now?
(After selecting the asteroid layer, it was unable to find a bright one.)

thanks,
adam
 
Hi Adam,

I assume you refer to the AnnotateImage script. We haven't implemented any changes that could affect its behavior with XEPH layers. Can you please upload the image, so I can try to reproduce the problem?
 
Juan,
Sorry... false alarm- I made some mistakes.
I forgot I needed to add the custom XEPH files. (I thought this would be remembered).

However, the date I need to investigate is 2022-02-20 ...
I assume I need to re-download these files?

-adam
 
The XEPH files contain ephemerides from 2019-12-02 to 2023-01-01, so there should be no problems. If the asteroid is from the big boys set (343 most massive bodies), the time span is from 1550 to 2650, so there are no issues either.
 
Juan Conejero said:
The XEPH files contain ephemerides from 2019-12-02 to 2023-01-01, so there should be no problems. If the asteroid is from the big boys set (343 most massive bodies), the time span is from 1550 to 2650, so there are no issues either.
Click to expand...

This is what I am seeing concerning the range error.
 

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Great! I'll start the generation of new ephemerides in a few days. We have a set of new tools based on astrometry and ephemerides on the design board. They will be very funny :)
 
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