Overview:
Prospects for life on:
1. Europa (Jupiter moon)
2. Titan (Saturn’s moon)
3. Enceladus (Saturn’s moon)
Life on Europa?
NASA’s JUNO mission to Jupiter:
Juno arrives at Jupiter
in 2016
Science goals:
1.
2.
3.
4.
abundances (e.g. ratio of O/H)
determine core mass
map the gravitational and magnetic field
map the variation in atmospheric composition, temperature structure,
cloud opacity and dynamics
Life on Europa?
• Europa is the sixth of Jupiter's known satellites and the
fourth largest; it is the second of the Galilean moons.
Europa is slightly smaller than the Earth's Moon.
Galileo Galilei
Europa
1610!
Life on Europa?
• Spacecraft exploring the Galilean satellites:
Voyager 1 & 2
Galileo
Europa:
Europa’s surface is smooth and young (no craters), and is covered with
cracks:
Europa is tidally heated like Io (just less)
and has maybe the youngest surface in
the outer solar system!
Icebergs on the surface moved
by liquid water that later froze or
by slushy warmer ice beneath?
Europa
Thera Macula & Thrace Macula
Conamara Chaos
Ridges
Cycloids
Plains
Oceans – EUROPA has more water than total water on earth
The Saturn System
Titan:
• The biggest moon of Saturn
• Cold! 75 K (-180 C) - turns methane and other gases to
liquid Its orange because of that.
• It’s made up of about half rock and half frozen water
• THICK ATOMSPHERE - The atmospheres pressure is 1.5
times Earth’s
• 90 to 99% of the gas is Nitrogen. The rest is methane and
very small amounts of hydrogen cyanide and acetylene.
Origin?
– Probably outgassing after formation by accretion of icy
planetesimals/comets and subsequent evolution
– Methane from cryovolcamism
Titan:
• Exploring Titan:
Voyager 1 & 2
Cassini / Huygens
Titan:
• Titan as seen from space:
visible
938nm
methane
window
Different views based on the type of filters used
composite
First real look at Titan in 1979 with Voyager flyby
Atmosphere so dense
the surface is not
visible
Atmosphere primarily
nitrogen (like Earth)
but clouds are
aerosols (smog) of
some sort
25 years later…another spacecraft on a mission
The Cassini and
Huygens
spacecraft
The Huygens
lander
Concept of the Huygens lander…an artist’s conception
The Huygens Probe
Part of the Cassini mission
Landed on Titan 1/14/05
Pictures of Titan from the approaching Cassini
spacecraft
Image at infrared wavelengths
Near-IR
image
penetrates
the haze
and sees
surface
features
Near-IR
image (933 nm)
The Sea?
The Lake?
Titan has flow channels, too
The view from Huygens on the way down
On the surface
“rocks” are blocks of ice
The most remote human “base” in
the universe: nearly a billion miles
from the Sun
Cassini radar shows lakes of methane
Recent
observations
from Cassini
show
different
manifestation
of methane
lakes:
sunlight glints
from the lake
surfaces
The surface of Titan: an artist’s view
Enceladus:
Brightest object in Solar System
except the Sun.
Something has erupted to make
the planet so smooth (water,
volcanic, etc…)
Named after a Titan that was
killed by Athena
Enceladus:
Enceladus has the highest albedo (>0.9) of any body in the
solar system. Its surface is dominated by fresh, clean ice.
At least five different types of terrain have been identified on
Enceladus. In addition to craters there are smooth plains and
extensive linear cracks and ridges. At least some of the surface
is relatively young, probably less than 100 million years.
This means that Enceladus must have been active until very recently (and
perhaps is still active today).
Enceladus is much too small (500km) to be heated solely by the decay of
radioactive material in its interior at present. But briefly after its formation 4.5
billion years ago short-lived radioisotopes may have provided enough heat to
melt and differentiate the interior. That combined with modest present day
heating from long-lived isotopes and tidal heating may account for the
present day activity on Enceladus.
Enceladus:
Enceladus orbits in the densest
region of Saturn’s E-ring
Is it the source?
Enceladus is currently in a 2:1 mean motion orbital resonance with
Dione, completing two orbits of Saturn for every one orbit completed by
Dione. This resonance helps maintain Enceladus's orbital eccentricity
(0.0047) and provides a heating source for Enceladus's geologic activity
Geysers
Gas and dust plumes from
occultation photometry.
V=600 km/s
March 2008
Cassini flyby
Enceladus:
Cassini discovers jet-like plumes rising from the south polar regions.
During “fly-throughs” the spacecraft detected mostly water vapor, as well
as minor components like molecular nitrogen, methane and CO2.
Enceladus:
Cassini measures mean density:
1.6 g/cm3 => some % of silicates & iron
Now two heat sources:
1. Radioactive decay
2. Tidal forces
Possible molten core or magma pockets that
drive volcanism!
Enceladus:
The “Tiger Stripes” in the south
polar region.
Thermal map of cracks near south
pole of Enceladus. High temperatures
around 180 K (-135 F), normal = 72 K
“Tiger Stripes”
Enceladus
Tiger Stripes
IR-bright
emission
near the
south pole
of
Enceladus
Enceladus up close
Enceladus: another case in which
subsurface water flows up through
cracks to the surface of the object
Europa’s surface
Europa’s
surface
No organics
detected yet.
Our best chance
of reaching the
ocean may be
these features.
If they are cracks
they may contain
ocean material
Or plumes ??
Summary:
•
Europa likely has a liquid sub-surface ocean and
is heated by tidal forces
•
Titan has complex organic chemistry and a thick
nitrogen atmosphere (early Earth)
•
Enceladus is geological active, has lots of water,
plus some organic material and a heated interior