S/2019 S 1

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S/2019 S 1 is ∼5 kilometers in size and thus a small irregular moons of Saturn. Its discovery has been announced in 2021. Its mean distance to Saturn is ∼11¼ million kilometers, with one revolution around the planet on a prograde orbit requiring 1 year, 2 months and 2½ weeks. This moon might be a collisional remnant of Kiviuq and/or Ijiraq which share very similar orbital elements. Joint with these two moons, its mean distance to Saturn is the lowest and its orbit period the shortest of all irregulars. S/2019 S 1 is a member of the Inuit dynamical group.

With an average eccentricity of ∼0.46, the orbit of S/2019 S 1 is quite elongated. This brings this object closer to Saturn than any other known irregular moon, occasionally even below 4 million kilometers (= 4 Gigameters = 4 Gm). For example, according to JPL’s Horizons orbit calculator, on 19 Jul 2003, the periapsis distance of S/2019 S 1 was just 3.68 Gm. Note that Iapetus, the outermost of Saturn’s large moons, orbits Saturn at a distance between 3.46 and 3.66 Gm. Thus, S/2019 S 1 and Iapetus are “hot” candidates for a future collision, which has so far been prevented by the orientations of the orbits as well as by “bad” timing of potential orbit-crossing point passages. Indeed, these two moons came closer than ∼2 Gm to each other multiple times in the past millenium, and will do so frequently in the future. A collision would vaporize S/2019 S 1 and produce a crater on Iapetus with a size of ∼100 kilometers — that’s a really big one!

We made no attempt to observe S/2019 S 1 with the Cassini spacecraft because it was unknown at the time Cassini was active. If known, Cassini’s closest approach of 2.1 million kilometers in September 2015 — a record approach distance to an irregular moon except for the targeted Phoebe flyby — would have been a great opportunity to take data.

Table of contents

(1) Astronomical and physical properties

This page is intended to compile (much of) our knowledge of unnamed moon S/2019 S 1 in compact form, including general information like discovery circumstances and orbital and physical parameters. For further reading on irregular moons of Saturn in general, see the reference list at my outer-Saturnian moons page.

Last update: 29 Apr 2022 — page content is best displayed on a screen at least 1024 pixels wide


(1) Astronomical and physical properties

Moon name Saturn range Orbit period Orbit direction Size Rotation period Discovery year
S/2019 S 1
million km
years
prograde
km
unknown
2019

Basic information about S/2019 S 1 is offered in tabular form:
(1A) Basic properties
← Table (Basic properties) in text format [ not available yet ]

Most fundamental values are highlighted in red. The notes offer explanations, calculations, accuracies, references, etc. The data were obtained from ground-based observations.

(1A) Basic properties
Moon name(1) Orbit direction(7) prograde Mean size(11) ∼ 5 km
Moon abbrev.(2) 19S1 Semi-major axis(8) 11.246 ⋅ 10km Absolute visual magnitude(12) ∼ 15.3 mag
IAU number(3) Orbit eccentricity(8) 0.463 Apparent vis. mag. from Earth(13) 24.4 mag
Provisional desig.(4) S/2019 S 1 Orbit inclination(8) 48.7° First observation date(14) 01 Jun 2019
SPICE ID(5) 65093 Orbital period(8) 445.5 d Announcement date(14) 16 Nov 2021
Also-used label(6) Group member(9) Inuit MPEC announcement(14) 2021-W14
Dynamical family(10) Kiviuq/ Ijiraq Discoverers(15) E. Ashton et al.

Table notes:

(1) The object has no proper name yet.

(2) I use this 4-letter abbreviation in the diagrams of my publications simply for practicability reasons. These have no offcial character.

(3) Moon numbers are assigned by the International Astronomical Union (IAU)’s Committee for Planetary System Nomenclature. For satellites, Roman numeral designations are used.

(4) Designation given to the object in the first announcement; the guidelines are explained here.

(5) SPICE is a commonly-used information system of NASA’s Navigation and Ancillary Information Facility (NAIF). It assists engineers in modeling, planning, and executing planetary-exploration missions, and supports observation interpretation for scientists. Each planet and moon obtained a unique SPICE number. In case of this object, the number is still provisional.

(6) ‘S’ for ‘Saturnian moon’ plus the roman numeral designation in arabic numbers are often-used labels for satellites. Not sure how official that is.

(7) Prograde (counterclockwise as seen from north) or retrograde (clockwise as seen from north).

(8) Orbit semi-major axis a, eccentricity e, inclination i, orbit period P; from JPL’s Solar System Dynamics Planetary Satellite Mean Elements website.

(9) Norse, Inuit, or Gallic.

(10) Classification based on the a,e,i space in Fig. 1 and Table 2 in Denk et al. (2018).

(11) Determined from absolute visual magnitude H (see note (12)). The conversion from H to size (diameter of a reference sphere) was calculated through $D=1 \text{ au}\cdot \frac{2}{\sqrt{A}}\cdot 10^{−0.2·(H−M_☉)}$; with solar apparent V magnitude M = −26.71 ± 0.02 mag and Astronomical Unit 1 au = 149 597 870.7 km. For the object’s albedo A, a value of 0.06 is assumed (see discussions in Grav et al. (2015) and Denk et al. (2018) on albedo uncertainties). Due to the uncertain input values, a size determined this way may be uncertain to ∼ −15/+30% (for A ± 0.02 and H ± 0.1).

(12) From MPEC; the number may be uncertain by several tenths of magnitude. The absolute visual magnitude HV is the magnitude (brightness) of an object (in the visible wavelength range) if located 1 au away from the sun and observed at 0° phase angle (i.e., in this definition, the observer virtually sits at the center of the sun). The magnitude scale is logarithmic, with an object of 6th mag being 100x darker than a 1st mag object.

(13) Apparent visual magnitude V; from S. Sheppard’s website.

(14) The date of the photography wherein the object was spotted for the first time is given in the MPEC released on the announcement date.

(15) The discoverer team included: Edward J. Ashton, Brett J. Gladman, Matthew Beaudoin, Jean-Marc Petit, Mike Alexandersen.


© Tilmann Denk (2022)