Moons of Jupiter and Saturn
Oct 7, 2015
A wealth of worlds
of ice and rocks
>170 moons orbit jovian planets
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
(Jupiter)
Triton
Enceladus Titan
(Neptune)
(Saturn)
NOT SO!
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’)
Plus: moons have large percentage of ice!
JUPITER SYSTEM
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
Galilean moons of Jupiter
Io, Europa, Ganymede, Callisto
Laplace resonances of
Io, Europa and Ganymede
Laplace resonance:
• 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!
Ganymede – king of the moons
R = 2634.1±0.3 km (0.4 REarth)
global geologic map
Ganymede:
• orbital period is 7 days 3h.
• Tidally locked
• Orbit radius 1,070,400 km
Undersurface water ocean on Ganymede
how do we know?
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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)
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
Galileo image of cratered plains
Voyager 1 image of Valhalla, a multi-ring impact structure
3800 km in diameter
Callisto base
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;
SATURN SYSTEM
Moons of Saturn:
So far, 62 moons have been discovered in orbits around Saturn, and 53 of them have
been officially named.
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).
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
Mimas
Iapetus
Tethis
Rhea
Dione
“Pac-Men”
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High-energy electrons
bombard low latitudes
on the leading side of a
moon, turning a fluffy
icy surface into hardpacked 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.
Rhea
Iapetus
Hyperion
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irregular shape
chaotic rotation
sponge-like
appearance
Phoebe
Cassini-Huygens (2004-2017)