Comparison of the Gaia-CRF3 and planetary ephemerides via asteroid observations

¹ School of Astronomy and Space Science, Key Laboratory of Modern Astronomy and Astrophysics (Ministry of Education), Nanjing University, 163 Xianlin Avenue, 210023 Nanjing, PR China
² University of Chinese Academy of Sciences, Nanjing 211135, PR China
³ Research Center for Computing, National Research and Innovation Agency, Bogor, Indonesia

^★ Corresponding author: jcliu@nju.edu.cn

Received: 8 October 2024
Accepted: 14 July 2025

Abstract

Context. The Gaia satellite provides high-precision astrometric observations of Solar System objects, achieving positional accuracies at the milliarcsecond (mas) level. As the Gaia Celestial Reference Frame (Gaia-CRF3) serves as the optical realization of the International Celestial Reference System (ICRS), these observations offer a new means to assess the alignment between planetary ephemerides and the ICRS.

Aims. We aim to evaluate the orientation and rotational alignment between Gaia-CRF3 and the dynamical reference frame defined by planetary ephemerides.

Methods. We analyzed a sample of 1001 asteroids with high-quality Gaia observations. Their osculating orbits were computed using data independent of Gaia, under the Solar System dynamical model DE440, and were propagated to the epochs of Gaia observations. Positional differences between the propagated ephemerides and Gaia astrometry were used to estimate orientation offsets and rotation rates.

Results. Using a least-squares fit based on along-scan (AL) residuals, we derived orientation offsets of about 10 mas and rotation rates less than 0.5 mas yr⁻¹ in the equatorial coordinate system. The robustness of these solutions was verified through iterative fitting and validated by both model-based and sample-based tests. When Gaia observations are incorporated into the orbit determination process, the orientation offset decreases dramatically to approximately 0.2 mas.

Conclusions. Our analysis reveals orientation offsets of approximately 10 mas, significantly larger than the reported DE440-ICRF3 discrepancies. This discrepancy likely stems from systematic biases inherent in historical asteroid astrometry. The inclusion of Gaia observations reduces these offsets to the sub-milliarcsecond level, demonstrating their crucial role in aligning dynamical ephemerides with the ICRS.