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I'm using the website of NASA JPL Horizon system at this link Small-Body Database Query to download a database of orbital elements for NEOs (asteroids and comets).

Although I checked the Horizons System manual at this link Horizon System manual, I cannot understand what is the heliocentric inertial reference frame used to compute these data.

Can you help me?

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    $\begingroup$ I believe it is using the J2000 frame (Earth equatorial, or Earth Mean Equator EME2000) judging from clicking on Ceres it shows the reference frame: ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?des=1 $\endgroup$ Jan 30, 2022 at 18:09
  • $\begingroup$ The frame used to numerically calculate the solar system ephemerides themselves, i.e. the massive bodies like the Sun, planets, their moons, and large asteroids can be read about in The JPL Planetary and Lunar Ephemerides DE440 and DE441 and the orbits of the lower mass objects like the rest of the comets and asteroids in the Small Body Database will be propagated using such an ephemeris. But I think you are asking what system they use to provide the small body ephemerides, not to initially calculate them? $\endgroup$
    – uhoh
    Jan 30, 2022 at 22:48
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    $\begingroup$ Thanks for the answer @uhoh. The point is: Which reference system should I refer to when reading the orbital elements (semi-major axis, eccentricity, inclination, and so on) that I download at the first link provided in the question? $\endgroup$
    – g_don
    Jan 30, 2022 at 23:01
  • $\begingroup$ So, do I assume that the data are referred to heliocentric IAU76/J2000 ecliptic reference frame? $\endgroup$
    – g_don
    Jan 31, 2022 at 0:02

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