Outer Moons of Jupiter

My DLR colleague Stefano Mottola and I perform an observation campaign of the irregular satellites of Jupiter to measure lightcurves for rotation period, spin-axis orientation, and shape determination. For this task, we use the 1.23-m telescope at Calar Alto in southern Spain which allows us to observe the ∼7 largest of Jupiter’s outer moons in greater detail. Mein DLR Kollege Stefano Mottola und ich führen eine Beobachtungskampagne der irregulären Jupitermonde durch, um Lichtkurven zur Bestimmung der Rotationsperioden, Polachsenausrichtungen sowie der Formen der Objekte zu erhalten. Für diese Aufgabe verwenden wir das 1.23-m Teleskop auf dem Calar Alto in Südspanien, mit dem wir die ∼7 größten der irregulären Jupitermonde im Detail studieren können.

Paper on Himalia’s rotation period: Pilcher, F., Mottola, S., Denk, T. (2012): Photometric Lightcurve and Rotation Period of Himalia (Jupiter VI). Icarus 219, 741-742. doi:10.1016/j.icarus.2012.03.021.

Paper on Cassini’s Jupiter flyby in Dec 2000, including observations of Himalia: Porco, C.C., 23 colleagues (2003): Cassini Imaging of Jupiter’s Atmosphere, Satellites, and Rings. Science 299, no. 5612, 1541-1547. doi:10.1126/science.1079462.
Another source for this paper is here. An excerpt of the part describing the Himalia findings can be found here.

Calar-Alto related webpages:
Weather forecast (continuous live data stream)
Current Meteosat weather picture
Calar-Alto webcams (continuous live data stream); the WEST and NORTH views show the 1.23-m telescope

Planning-related webpage:
HORIZONS Web-Interface

Table: Physical and astronomical properties of the largest irregular moons of Jupiter

Moon Spice ID1 Orbit2 Absolute magnitude
H [mag]3
Best apparent magnitude
Mean diameter
Rotation period
Semi-major axis
[million km]6
[ ]6
Orbital period
Moon (abbrev.)
Themisto 518 prograde 14.4 20.9 8 ? 7.51 0.242 43 0.36 The
Himalia 506 prograde 8.0 14.8 120×150 7.7819 11.46 0.162 28 0.69 Him
Elara 507 prograde 9.4 16.6 86 ? 11.74 0.217 27 0.71 Ela
Lysithea 510 prograde 11.3 18.3 36 (12.8) 11.72 0.112 28 0.71 Lys
Leda 513 prograde 12.7 20.0 20 ? 11.17 0.164 27 0.66 Led
Pasiphae 508 retrograde 10.2 17.0 61 ? 23.62 0.409 151 1.94 Pas
Sinope 509 retrograde 11.3 18.3 37 (13.2) 23.94 0.250 158 1.98 Sin
Carme 511 retrograde 10.8 18.0 46 (10.4) 23.40 0.253 165 1.92 Car
Ananke 512 retrograde 11.8 18.7 29 (8.3) 21.28 0.244 149 1.67 Ana

Table notes:

1…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.

2…The irregular satellites of Jupiter can be subdivided into objects with prograde and objects with retrograde orbits. The moons in the prograde Himalia group share an inclination close to 28°. The retrograde irregulars are more diverse, they orbit Jupiter in three distinct groups at inclinations ranging from 144° to 165°. The naming convention is that all prograde irregular moons of the Himalia group have names ending with an ‘a’, the retrograde moon’s names end with an ‘e’. As of end-of-Sep 2012, 7 prograde and 52 retrograde irregular Jovian moons were known; 12 of the retrogrades were in danger of being lost or effectively lost (Jacobson et al. 2012; see also JPL’s SSD websites).

3…The absolute magnitude and satellite diameters (except for Themisto) are taken from Rettig et al. (2001). They assume an albedo of 0.04 for all satellites. The axes of Himalia are from our Cassini work, published in Porco et al. (2003). The absolute magnitude is the magnitude (brightness) of an object if located 1 au away from the sun and observed at 0° phase angle (i.e., the observer virtually sits at the center of the sun in this definition). Smaller numbers indicate brighter objects. The magnitude scale is logarithmic, with an object of 6th mag being 100x darker than a 1st mag object. The conversion from absolute magnitude H to size is given by this formula or this table if the object’s albedo is given or reasonably guessed.

4…Best apparent magnitude as seen from Earth of each irregular moon at the 2012/2013 apparition. Smaller numbers again indicate brighter objects. The human eye can spot celestial objects down to ∼6th magnitude.

5…All values are synodic rotation periods. The Himalia value is from our Pilcher et al. (2012) paper. The Lysithea, Sinope, Carme, and Ananke periods are from Luu (1991). They are erroneous by ∼0.3 to ∼3.1 h and will be replaced by more accurate values soon. Rettig et al. (2001) observed Leda over three consecutive nights, but could not extract a rotation period. They thus note ∼24 h as a possible value for Leda, but I do not believe that. (A non-detection of a period does not necessarily point to a period close to Earth’s. It may also mean that the object is rather spherical with no prominent albedo markings, that its pole axis was pointing close to the observer, or that the observation’s signal-to-noise ratio was insufficient.)

6…The data for the orbital parameters are taken from Scott Sheppard’s website.

© Tilmann Denk (2017)