Context. The Yarkovsky effect is a weak non-gravitational force but may significantly affect subkilometer-sized near-Earth asteroids. Yarkovsky-related drift may be detected, in principle, from astrometric or radar datasets of sufficient duration. To date, the asteroid Kamo'oalewa, the most stable of Earth's quasi-satellites, has an ∼ 18 year-long arc of ground-based optical astrometry. These data provide an opportunity to detect the Yarkovsky effect acting on the asteroid Kamo'oalewa. Aims. We determined the Yarkovsky-related drift of asteroid Kamo'oalewa from ∼ 18 years of ground-based optical astrometry. Furthermore, we investigated the influence of the Yarkovsky effect on the orbital evolution of asteroid Kamo'oalewa based on this estimated value, and evaluated the potential improvements in the detection of non-gravitational accelerations (Yarkovsky effect and solar radiation pressure) for the asteroid Kamo'oalewa that could be provided by the future Chinese small-body exploration mission, Tianwen-2. Methods. The Yarkovsky-related drift of asteroid Kamo'oalewa was detected from the orbital fitting of the astrometry measurements. We checked the Yarkovsky effect detection based on both the orbit fitting results and the physical mechanisms of the Yarkovsky effect. Results. We report for the first time the detection of the Yarkovsky effect acting on asteroid Kamo'oalewa based on ∼ 18 years of ground-based optical astrometry data. The estimated semi-major axis drift is (-6.155 ± 1.758) × 10 −3 au/Myr. In addition, our numerical simulation shows that the Yarkovsky effect has almost no influence on the short-term orbital evolution of the asteroid Kamo'oalewa, but does have a long-term influence, by delaying the entry of the object into the Earth co-orbital region and accelerating its exit from this region, with a more significant signature on the exit than on the entry. In the context of spacecraft tracking data, the Tianwen-2 mission will improve both non-gravitational accelerations (Yarkovsky effect and solar radiation pressure) and predictions of its future ephemeris.

Context. Accurate gravity and ephemerides estimations for Neptune and its satellites are necessary for the forthcoming deep space exploration missions targeting its system. In addition, these estimations are also meaningful for the modeling of Neptune's interior and for solar system dynamics studies. The body of astrometric data concerning Triton has been accumulating for about two hundred years, but more accurate updates to the ephemerides of this moon and revisions to the relevant gravity parameters would be possible with more precise astrometric data. The new Gaia catalog of star positions plus observations from Voyager 2 and the Hubble Space Telescope provide such a basis for high-precision astrometry and to complement and extend the existing body of data. Aims. We aim to report integrated orbital fits for Triton based on all the available astrometric data from 1847 to 2020, including observations from Earth-based telescopes, Voyager 2, and the Hubble Space Telescope. We also estimate the Neptunian gravity using the motion of Triton. Methods. Triton’s orbital solution was determined by a weighted least-squares method to fit the model to the most complete astrometric data set to date. The DOP853 algorithm was adopted in the numerical integration calculations. For the dynamical model parameters, our orbital model for Triton is similar to the NEP081 but with an update. The perturbations from the inner satellites (Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, and Hippocamp) were considered by adding corrections to J2 and J4 for Neptune. As the gravitational oblateness coefficient of Neptune is correlated with its orientation, the pole parameters were thus kept fixed in the integration when estimating Neptunian gravity. A Monte Carlo analysis was performed, however, to obtain reliable accuracy estimations and to assess the uncertainty of pole parameters on the results’ formal error. Results. We provide a new orbit and dynamical model values for Triton. The estimated accuracy of the model we built and updated fit all the astrometric data. The RMS of the residuals was 0.074 arcsec in the right ascension and 0.071 arcsec in declination. The RMS was 0.102 arcsec for X and 0.139 arcsec for Y in differential coordinates. The RMS for the position angle was 0.834 degrees, and the angular separation distance was 0.257 arcsec for the data collected before 1960. The orbit of Triton was well determined with the orbit differences from NEP081 and NEP097 (so far the latest Triton ephemerides from Jet Propulsion Laboratory) as being less than 300 km (about 15 mas) during the observation coverage period of this study. The large body of astrometric data for Triton over a time interval from 1847 to 2020 was used to constrain its position at the initial epoch, allowing us to reduce formal uncertainty to about 3 km. Based on the most complete weighting astrometric observations of Triton, the estimated mass of the Neptune system is GMs = 6 836 525.210 ±19.526 km3 s−2. Our revised gravity model yields J2 = 3401.655 ±1.850 × 10−6 and J4 = −33.294 ±10.000 × 10−6. The astrometric observations showed little sensitivity to GMs and J4, but acted well on J2. A Monte Carlo method was used to analyze the error caused by a variation in the pole parameters and showed that J2 = 3401.655 ± 3.994 × 10−6 was a more realistic error.