The orbit of Triton with new precise observations and the INPOP19a ephemeris

Abstract

Aims. The Gaia catalogue brings new opportunities and challenges to high-precision astronomy and astrometry. The precision of data reduction is therefore improved by a large number of reference stars with high-precision positions and proper motions. Numerous precise positions for Triton are obtained from the latest observations using the Gaia catalogue. Furthermore, the new INPOP19a planetary ephemeris, which also fits the observations from the Gaia Data Release 2, has recently become available. In this paper, a new orbit of Triton is calculated using the latest precise charge-coupled device (CCD) observations and the INPOP19a ephemeris. Methods. Triton’s orbital solution is calculated using a numerical integrator, while the orientation of Neptune’s pole in particular is obtained by integrating the simplified Euler’s equations of motion. We determine the orbit of Triton over 170 yr based on 11 040 Earth-based observations made between 1847 and 2016 and on Voyager 2 data. The positions of the Sun and planets are provided by the INPOP19a ephemeris. We compare our results to those from other previous works to check the influences on Triton’s orbit from different planetary ephemerides. Results. A new orbit of Triton is provided here. The root-mean-square of the residuals for the Earth-based CCD absolute observations are 0.102″ in right ascension and 0.142″ in declination. Although most different planetary ephemerides have large differences in Neptune’s position, the orbits of Triton using different planetary ephemerides are still close, under similar dynamical models. The Voyager 2 data add a constraint on Triton’s orbit here.

The Neptunian gravity estimated from the motion of Triton based on astrometric observations

“…We also used about 40 differential coordinates of Triton from HST Additionally, we used the observations from Voyager 2 published by Jacobson (1991). These observations were also used in orbit determinations by Emelyanov & Samorodov (2015) and Tang et al (2020). The corresponding file vgr2-nep081.bsp 3 provides the positions of the Voyager 2 spacecraft that were used to calculate theoretical observations to compare with the measured data.…”

“…Its motion is influenced by Neptune's oblateness and solar planet attractions. Other satellites of Neptune also affect Triton's motion, but the perturbations are rather small and exert negligible influence on its motion, as considered in Jacobson (2009), Emelyanov & Arlot (2011), Emelyanov & Samorodov (2015), and Tang et al (2020). Triton's orbit, however, is strongly influenced by the perturbations from the inner regular satellites of Neptune, as indicated by the NEP097 ephemeris reported by the NASA Jet Propulsion Laboratory (Brozović, priv.…”

“…Voyager 2 provided the most accurate data for Triton (Jacobson 1991). The new Gaia catalog offers new opportunities for high-precision astrometry, and even early CCD images can also be reprocessed to get more positions with higher precision under the frame of Gaia DR2 (Tang et al 2020;Yan et al 2020). Importantly, all these astrometric observations of Triton could contribute to ephemeris precision and a new accurate background of the gravitational field.…”

“…Later, an analytical theory of Triton's motion fitting all published observations made from 1847 to 2012 was given by Emelyanov & Samorodov (2015). Tang et al (2020) corrected the initial states of Triton with some more new precise observations. Not only can Triton's orbit be refined through astrometric observations, but Neptune's pole orientation and gravitational harmonics can also be more accurately defined.…”

Orbits of the Irregular Satellites of Uranus and Neptune

“…As such, Triton is often kept in its own category (Burns 1986b;Goldreich et al 1989). Jacobson (2009) and Tang et al (2020) both reported on the ephemeris of Triton.…”