APPROX – mutual approximations between the Galilean moons: the 2016–2018 observational campaign

Abstract

The technique of mutual approximations accurately gives the central instant at the maximum apparent approximation of two moving natural satellites in the sky plane. This can be used in ephemeris fitting to infer the relative positions between satellites with high precision. Only the mutual phenomena -occultations and eclipsesmay achieve better results. However, mutual phenomena only occur every six years in the case of Jupiter. Mutual approximations do not have this restriction and can be observed at any time along the year as long as the satellites are visible. In this work, we present 104 central instants determined from the observations of 66 mutual approximations between the Galilean moons carried out at different sites in Brazil and France during the period 2016-2018. For 28 events we have at least two independent observations. All telescopes were equipped with a narrow-band filter centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The telescope apertures ranged between 25-120 cm. For comparison, the precision of the positions obtained with classical CCD astrometry is about 100 mas, for mutual phenomena it can achieve 10 mas or less and the average internal precision obtained with mutual approximations was 11.3 mas. This new kind of simple, yet accurate observations can significantly improve the orbits and ephemeris of Galilean satellites and thus be very useful for the planning of future space missions aiming at the Jovian system.

Characterization of the precision premium in astrometry

“…Precision premium can be used to improve the astrometric precision since its characteristics are clarified. The most direct application is in mutual approximation technique (Morgado et al 2016(Morgado et al , 2019. This paper demonstrates that the precision premium exists between any two objects with less than 100 arcsecs separation.…”

“…The mutual approximation technique chose arbitrarily the approximations for which the separation of satellite pair is smaller than 30 arcsecs. Morgado et al (2019) successfully used this technique to the Galilean satellites and obtained an average internal precision of 11.3 mas. The extremely high precision and practicability of this technique indicate that it has great potential in astrometry for some bright moving objects.…”

Arecibo Radar Astrometry of the Galilean Satellites from 1999 to 2016

“…Astrometry of the Galilean satellites was also reported in Morgado et al (2019aMorgado et al ( , 2019b. Morgado et al (2019a) measured instants of apparent encounters of satellites in the plane of sky from 2016 to 2018. This method consists of tracking the apparent distance between two satellites on the plane of sky and identifying the time when minimum distance occurs.…”

“…This type of measurement, described in Morgado et al (2016), is not tied to the geometry of mutual events and is supposed to achieve precisions better than 30 mas (90 km). Morgado et al (2019a) reported 14.4 mas as the rms of the residuals with respect to JUP310 and planetary ephemeris DE435 (Folkner 2016). Additionally, Morgado et al (2019b) reported a very precise measurement of Europa's position, with an uncertainty of 0.8 mas, based on the first stellar occultation.…”

The 2014–2015 Brazilian mutual phenomena campaign for the Jovian satellites and improved results for the 2009 events

“…For satellite-pair distances, the uncertainties are at the 30 mas level (∼ 90 km) (Peng et al, 2012). Mutual approximations, based in the same geometrical configuration of mutual occultations, achieve uncertainties at the 10 mas level (∼ 30 km) (Morgado et al, 2016(Morgado et al, , 2019.…”