1. Moons of Jupiter and Saturn
Oct 7, 2015

2. A wealth of worlds of ice and rocks
>170 moons orbit jovian planets

3. NOT SO! (Jupiter) (Neptune) (Saturn) Io Europa Triton Enceladus Titan
Most large Jovian Planet satellites are smaller than our moon. Based on the geological principles controlling Terrestrial Planets, we expect cold, dead worlds, covered by craters…
Io Europa Triton Enceladus Titan
(Jupiter) (Neptune) (Saturn)
NOT SO!

4. Tides: so what? Tides slow rotations
Synchronous lock moons (and planets!)
Tides distort moon’s shape - continually changing shape heats interior -> geological activity
Tides change the system (cause orbits to circularize)
Tides are stronger around more massive planets
Tides are stronger closer to the planet
Inside a few planetary radii, tides can pull a moon apart (or more likely, prevent it from accreting): (‘Roche tidal zone’)
Synchronous lock: Almost all satellites do this; Mercury does something similar with Sun; The Earth will someday keep same face toward the Moon; Many extrasolar planets probably keep one face to their suns
Plus: moons have large percentage of ice!

5. Jupiter system

6. Groups of Jupiter moons:
Regular:
Inner satellites or Amalthea group: Metis, Adrastea, Amalthea, and Thebe.
Main group or Galilean moons;
Irregular:
The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit
Inner satellites orbit very close to Jupiter; the innermost two orbit in less than a Jovian day.

7. Galilean moons of Jupiter
Io, Europa, Ganymede, Callisto (named for mythical lovers of the Roman god Jupiter, later run out of names)
With small sizes expected to be like the Moon – heavily cratered, geologically inactive, but not the case!
Io, Europa, Ganymede, Callisto

8. Laplace resonances of Io, Europa and Ganymede
The superior conjunction between Io and Europa always occurs when Io is at periapsis and Europa at apoapsis.
The superior conjunction between Europa and Ganymede occurs when Europa is at periapsis.
The longitudes of the Io–Europa and Europa–Ganymede conjunctions change with the same rate, making the triple conjunctions impossible.
the eccentricities get pumped up to much higher values than if the satellites were not in a resonance -> tidal heating -> geological activity!

9. Ganymede – king of the moons R = 2634.1±0.3 km (0.4 REarth)
global geologic map
the largest moon in the solar system, larger than Mercury!
Albedo = 43%, Near-infrared spectroscopy has revealed the presence of strong water ice absorption bands at wavelengths of 1.04, 1.25, 1.5, 2.0 and 3.0 μm
Water ice surface - Duality of terrains
Ganymede:
orbital period is 7 days 3h.
Tidally locked
Orbit radius 1,070,400 km

10. Old (more cratered, darker, must be billions years old) and new terrains – probably water erupting along cracks in ice

11. Undersurface water ocean on Ganymede how do we know?
Ganymede generates its own magnetic field
-> produces aurorae – strips of radiant electrified gas that circle Ganymede’s poles
Ganymede is close to Jupiter, any changes to Jupiter’s magnetic field directly affect that of Ganymede
when Jupiter’s magnetic field shifts due to the planet’s rotation, Ganymede’s aurorae “rock” back and forth
-> can make a model, and compare to the observational data
scientists surmised that an ocean works against Jupiter’s magnetic pull, causing Ganymede to rock less violently than they had anticipated (March 2015)
The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in After flybys of all three icy Galilean moons, the probe is planned to enter orbit around Ganymede

12. Callisto
Not fully differentiated (metal, rock and ice are still mixed throughout most of its interior)
No tidal heating (out of resonance)
far out of in Jupiter’s magnetic field
Anti-jovian side

13. Galileo image of cratered plains
Voyager 1 image of Valhalla, a multi-ring impact structure 3800 km in diameter
Galileo image of cratered plains
the crater density is close to saturation
Lacks volcanic and tectonic activity
Dark material is left behind after ice sublimation and bright patches are probably H2O frost

14. Callisto base

15. Exploration of Jupiter system
Past: Pioneers 10 and 11, Voyagers 1 and 2, Galileo, Cassini, New Horizons (in 2007);
Current:
Juno (arrival 4 July 2016)
Planned:
European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022;
NASA/JPL: Europa Multiple-Flyby Mission (formerly Europa Clipper), set for launch in 2020;

16. Saturn system

17. Moons of Saturn: So far, 62 moons have been discovered in orbits around Saturn, and 53 of them have been officially named.

18. From left to right the moons are Epimetheus (113 km/70 miles across), Janus (179 km/111miles), Prometheus (86 km/53 miles) and Atlas (30 km/19 miles).

19. Saturn's Medium-Size Moons
(300 — 1,500 km in diameter)
Saturn has 6 medium-size moons. In order of increasing distance from the planet, they are:
Mimas
Enceladus
Tethys
Dione
Rhea
Iapetus

20. Mimas enormous impact crater (named Herschel)
equatorial band on Mimas' leading hemisphere is significantly brighter in the ultraviolet than surrounding terrains, and it appears somewhat bluish.
This feature, similar to one on Tethys, was found to correlate with the predicted pattern of bombardment of the moons' surfaces by high-energy electrons trapped in Saturn's magnetic field.
This bombardment is thought to alter the surface ices on a crystalline scale and change their color. Later thermal observations by Cassini's Composite Infrared Spectrometer (CIRS) instrument showed that these features also form thermal anomalies on the surface, giving rise to the nickname "Pac-Man" features

21. Iapetus
Tethis
Rhea
Dione

22. “Pac-Men”
High-energy electrons bombard low latitudes on the leading side of a moon, turning a fluffy icy surface into hard-packed ice.
The altered surface does not heat as rapidly in the sunshine or cool down as quickly at night as the rest of the surface
The surface alteration is occurring more quickly than its recoating by plume particles.
because the altered region on Tethys, unlike on Mimas, is also bombarded by icy particles from Enceladus' plumes, it implies

23. Rhea
Iapetus
Rhea: is the second-largest of Saturn's moon. Rhea has rather a typical heavily cratered surface with some fractures, no endogenic activity
Iapetus: A further mystery of Iapetus is the equatorial ridge: runs along the center of Cassini Regio, about 1,300 km long, 20 km wide, and 13 km high.
-remnant of the oblate shape of the young Iapetus, when it was rotating more rapidly than it does today; - The ridge could be icy material that welled up from beneath the surface and then solidified; - a ring system accretion; - the result of ancient convective overturn; - none of these really explains why it is so equatorial!

24. Hyperion irregular shape chaotic rotation sponge-like appearance
Scientists attribute Hyperion's unusual, sponge-like appearance to the fact that it has an unusually low density for such a large object. Its low density makes Hyperion quite porous, with a weak surface gravity. These characteristics mean impactors tend to compress the surface, rather than excavating it, and most material that is blown off the surface never returns

25. Phoebe
Kuiper belt object

26. Cassini-Huygens ( )