Transcript Globular Cluster Formation in CDM Cosmologies

Chapter 13: Europa
Voyager 2 flyby
Jupiter’s Moons
(28 in all)
4 Galilean moons (each
comparable with Earth’s
moon);
Io & Europa have thick rocky
mantles surrounding
iron/nickel cores & Europa has
water/ice outer shell 100-200
km thick
Ganymede & Callisto
deficient in rocky materials
Internal structure of the
Galilean Moons:
Densities of Moons
decreases steadily with
distance from Jupiter:
Rocky mantles for Io and
Europa to rock-ice mix of
Callisto:
3500 kg / cubic metre down
to 1900 kg / cubic metre
• Jovian system of Moons is
much like a mini-Solar
system in properties of its
Moons.
Europa – 9.38 Jovian radii out, smooth icecovered moon
Resolution in a) is
5km, in d) it is 20m
(taken by Galileo).
- little cratering ->
surface is being
reworked…. By tidal
flexing due to Jupiter?
- Ice flows?
Europa’s ice covered ocean - possible life?
Evidence for liquid ocean: Europa has a weak magnetic field!
a) Frozen surface of Europa, “pulled apart terrain” - (as in sea
ice) upwelling material filling gaps between separating ice
sheets b) water has flooded section of the surface -> liquid
ocean 100 km deep, beneath this surface?
Antarctica from
space:
- enormous
mass of ice
(Ross ice shelf)
floats on the
Antarctic ocean
- what can be
learned by
comparing
these images
with those of
Europa?
Properties of Europa:
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Reflectance spectra: surface composed mainly of
water ice.
Orange-brown markings indicate sulfur compounds from volcanic activity of Io!
Two major features of ice:
i) splotches (chaotic terrain) – covering nearly ½ of
surface – indicative of convection/upwelling
and ii) lines (ice tectonics) – densely packed overlaid
ridges, cracks, bands – indicative of plate
motion/collision
Paucity of craters -> resurfacing in a period of < 50Myr.
Models: Ice at least 10 km thick, ocean up to 100 km
deep…
Tidal force – the difference that gravity makes…
(a) Gravitational force
of the Moon at different
points on Earth’s
surface
(b) Difference between
Moon’s gravitational
force at Earth’s centre
and points on its
surface – very weak!
GET: surface distortion –
the TIDES
Side closest to Moon pulled away,
side farthest away “left behind”
Tidal locking: eg. slowing the spin of the Earth
Tidal force of Earth on Moon has locked Moon’s spin to same
value as orbital period…..…..same face always to the Earth.
Tidal force of the Moon on the Earth is slowing Earth’s spin by
…1.5 milliseconds per century.
How? Earth rotates – carrying bulge with it – offset with
respect to Moon - Earth line: Moon’s gravity tugs back at
the bulge, slowing rotation rate of Earth….
Earth’s spin
slows and
angular
momentum
transferred to
Moon – which
moves out.
Tidal heating in Io and Europa:
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Jupiter exerts very powerful gravitational force on inner moons.
These are *not* tidally locked however!
Io and Europa: prevented by perturbations from
Io/Europa/Ganymede system in 1:2:4 resonance.
Drives system into eccentric orbits
-> can’t come into synchronous state
-> bulge always faces Jupiter, but Io cannot keep same face
towards Jupiter – so bulge constantly distorts surface
-> huge constant tidal heating of the interior – which
Tidal heating – from dissipation of energy in tidal bulge - drives
the volcanism in Io (100 million megawatts)
….. And distortion of Europa and its ice cover (6 million
megawatts)
Life on Europa?
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Mission
concept: drill
through ice
of Europa to
explore for
possibility of
life in ocean
beneath
surface.
Tidal heating of Europa
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Resurfacing/cracking -> exposure of oceanic water
through crust to surface.
Cracks open and close; tidal time-scale -> days
Water/slush forced to surface, and then flows back…
bringing back surface chemicals
These include cometary material (organics), hydrogen
peroxide (H2O2), …
Photosynthesis might be possible in open cracks
Energy source for life… use hydrogen peroxide to
oxidize reductants such as H, H2S,… chemosynthesis
** Also possible – hydrothermal based life from
underwater volcanos?
Life probably a very sparse biosphere by Earth
standards..
The future… terrestrial planet finder(s):
coronograph (left), interferometer (right)