Prospects for Life in the Solar System

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Prospects for Life in the Solar System

• Conditions and evidence to date

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Promising Unpromising

• Mars
• Jupiters moons Io, Europa
• Saturns moons Titan, Enceladus

• Mercury
• Venus
• Earths Moon
• Jupiter, Saturn, Uranus, Neptune
• Pluto

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Why Unpromising?

• Mercury
• surface too hot (467C) / cold (-170C), no
  atmosphere, intense radiation (but magnetic
  field)
• Venus
• Surface too hot (462C), thick atmosphere
  CO2/N2, no liquid on surface (no magnetic field,
  but similar internal composition)
• Earths Moon
• no atmosphere, too cold, radiation
• Jupiter, Saturn, Uranus, Neptune
• no solid surface (no place for liquid to
  accumulate)
• Pluto
• too small for atmosphere, too cold

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Extremophile requirements

• Energy source for warm temperatures
• Liquid solution for locomotion, transport of
  nutrients
• atmosphere (development of eukaryota)

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Extremophile Heat Source

• Most critical to astrobiologists studying
  Jupiter's moons, the eccentricity or oval shaped
  orbits of Jupiter's moons are pumped or
  oscillated by tidal forces as they orbit.
• this input of Jupiter's gravitational energy
  heats up the inner moons particularly like Io
  without relying only on the Sun's radiant heat,
  and thus gives an interesting way to provide one
  of the three ingredients for life--an energy
  source--even if far from the Sun.

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Jupiters Galilean Satellites

• Io Europa Ganymede Callisto

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Sizes and orbits(note all moons are tidally
locked 11)

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Unlikely Moons
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Earths Moon

• This false-color image shows the Moon's soil and
  mineral compostion.
• Mare Tranquillitatis - the 'Sea of Tranquility' -
  is the dark blue region on the right.
• Scientists believe that the Moon was formed
  approximately 4.5 billion years ago (the age of
  the oldest collected lunar rocks).
• When the Moon formed, its outer layers melted
  under very high temperatures, forming the lunar
  crust, probably from a global "magma ocean."

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Ganymede
This shows an entire hemisphere of Ganymede. The
prominent dark region, called Galileo Regio, is
about 3,210 km in diameter. The bright spots are
relative recent impact craters. Part of the
Galileo Regio may be covered with a bright
frost There is a faint ozone / O2 atmosphere from
ioinizing radiation from Jupiter Has a complex
surface with some tectonic-like features No
evident liquids
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Callisto
This image shows the heavily cratered surface of
Callisto (the most heavily cratered object in the
solar system). It was taken by Voyager 2 on July
7, 1979. An enormous impact basin with
concentric rings is located near the top and
slightly left of center The surface is 4 By with
no sign of any surface activity
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Promising Moons
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Io Jupiters pizza moon

• Io is the most volcanically active planet or moon
  in the solar system
• tides drive the surface elevation to vary by up
  to 100 m (330 ft)
• much of its subsurface crust is in liquid form,
  seeking any available escape route to the surface
  to relieve the pressure
• the surface of Io is constantly renewing itself,
  filling in any impact craters with molten lava
  lakes and spreading smooth new floodplains of
  liquid rock.

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Io plumes visible from Earth
A volcanic plume rises from Io (lower left edge).
Credit NASA
Io passing in front of Jupiter
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Galileo probe captures eruption

• The Galileo spacecraft caught this volcanic
  eruption at Io's Tvashtar Catena region in 1999
• only a third the size of Earth and five times as
  far from the Sun, Io generates twice our total
  terrestrial heat bill
• tallest volcanic mountain 52,000 ft (2 x Mt.
  Everest)
• volcanoes erupt large quantities of sulfur-rich
  gaseous plumes and silicate magma
• thin atmosphere probably sulfur dioxide

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Io (seen with Europa)

• no liquids on surface
• underneath the crust lies a core of iron and
  iron sulfide
• this molten center is likely about half the
  moon's total observed size.
• this iron core rotates internally as Io's
  orbit passes through the intense magnetic fields
  that circumscribe Jupiter.

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Saturns second-largest moon Rhea
This artist's conception provided by NASA shows
the ring of debris that may orbit Saturn's
second-largest moon, Rhea, shown at left. These
new observations, detected by the Cassini
spacecraft suggest Saturn's second-largest moon
may be surrounded by rings, possibly the first
time a ring system has been found around a
moon. (AP Photo/NASA/JPL/JHUAPL)
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Europa

• like the Earth, Europa is thought to have an iron
  core, a rocky mantle, and a surface ocean of
  salty water.
• Unlike on Earth, however, this ocean is deep
  enough to cover the whole surface of Europa, and
  being far from the Sun, the ocean surface is
  globally frozen over.

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Europa Special Features

• long streaks on surface, some 20 km wide
  (volcanic ridges?),
• underground ocean (water?, with extremophiles?),
  
• very smooth surface with few craters (young,
  with mushy layer?)
• weak magnetic field that varies according to
  orbit around Jupiter (a conducting layer salty
  ocean beneath surface?)
• possible presence of liquid water and volcanism
• may be heated by tidal friction (like Io)
• Surface Temperature 170 ºC
• Atmospheric Composition O2 (trace, not
  biological)

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Europa Missions

• Pioneer 10 (NASA) flyby in 1973
• Pioneer 11 (NASA) flyby in 1974
• Voyager I fly-by (NASA) launched
• Galileo (NASA) Launched 1989 6 year journey
  (fly-by of Venus and Earth in 1990, again in
  1992)
• Made extensive surveys of the Jovian moons 8
  years 35 orbits of Jupiter!
• Galileo was deliberately crashed in to Jupiter
  September 21, 2003 - to avoid possibility that it
  might crash into Europa and contaminate any life
  that might be there.

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Europa Ridges / Ice
Some regions look like pack-ice on polar seas
during spring thaws on Earth
dark streaks crisscrossing the entire globe
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Arctic Ice Europa?
Views of Arctic ice on Earth, similar to Europa
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Europa Craters
The impact crater Pwyll may represent one of the
youngest features on Europa
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Europa movie
In this movie Europa is seen in a cutaway view
through two cycles of its 3.5 day orbit about the
giant planet Jupiter. Like Earth, Europa is
thought to have an iron core, a rocky mantle and
a surface ocean of salty water. Unlike on Earth,
however, this ocean is deep enough to cover the
whole moon, and being far from the sun, the ocean
surface is globally frozen over. Europa's orbit
is eccentric, which means as it travels around
Jupiter, large tides, raised by Jupiter, rise and
fall. Jupiter's position relative to Europa is
also seen to librate, or wobble, with the same
period.
http//solarsystem.nasa.gov/multimedia/videos/PIA1
0149.mov
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Europa movie
This tidal kneading causes frictional heating
within Europa, much in the same way a paper clip
bent back and forth can get hot to the touch, as
illustrated by the red glow in the interior of
Europa's rocky mantle and in the lower, warmer
part of its ice shell. This tidal heating is
what keeps Europa's ocean liquid and could prove
critical to the survival of simple organisms
within the ocean, if they exist. The giant
planet Jupiter is now shown to be rotating from
west to east, though more slowly than its actual
rate.
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Enceladus
Enceladus as viewed from NASA's Cassini
spacecraft. Smooth bright surface, high albedo,
reflects 100 of sunlight Surface temperature
-200C Parts of Enceladus shows craters no larger
than 35 km in diameter. Other areas show regions
with no craters indicating major resurfacing
events in the geologically recent past. There
are fissures, plains, corrugated terrain and
other crustal deformations.
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View of Enceladus just outside an edge-on view of
the Saturnian ring system Enceladus is only 500
km in diameter.
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Enceladus

• The leading hemisphere of Enceladus displays a
  remarkably fresh-looking surface in this recent
  Cassini view.
• At this resolution, only a few craters can be
  made out in this wrinkled region of the
  geologically active moon's surface.
• A far more heavily cratered, and older, terrain
  region is visible to the northwest.

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South Polar Terrain
Basemap of SPT showing tiger stripes,
cratering, and ridges
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Tiger Stripes
A sequence of broad depressions (2 km wide, .5
km deep and 100 km long) near STP B close up of
ridges separating the depressions C close up of
tiger stripes D enlargement of portion of C
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Plumes
Cassini's visual and infrared mapping
spectrometer measures the spectrum of the plumes
originating from the south pole of the icy moon,
capturing a very clear signature of small ice
particles.
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Plumes
The imaging team produces the first pictures of
the plume of icy material streaming from
Enceladus' south pole, possible evidence of
Yellowstone-like geysers fed by reservoirs of
liquid water.
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Plumes
The plumes are dynamic features, seen in two
images 1 month apart
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Enceladus Close Up
This three-image mosaic is the highest resolution
view yet obtained of Enceladus' north polar
region. The view looks southward over cratered
plains from high above the north pole of
Enceladus. Image credit NASA/JPL/Space Science
Institute
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Titan

• Encircled in purple stratospheric haze, Titan
  appears as a softly glowing sphere in this
  colorized image taken one day after Cassini's
  first flyby of that moon.
• This image shows two thin haze layers.
• The outer haze layer is detached and appears to
  float high in the atmosphere.
• Because of its thinness, the high haze layer is
  best seen at the moon's limb.

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Titan

• An image of Titan taken with the W.M. Keck II
  telescope on December 3, 2001.
• Complex bright and dark features around Titan's
  "continent" can be seen at their highest
  resolution ever.
• Several small bright clouds can also be made out
  near Titan's south pole.

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Cassini images
methane-containing clouds near the S. pole of
Titan
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Titan atmosphere

• Visibile light cannot escape from the veil of
  orange smog that covers Titan's surface
• The moon's dry cold atmosphere causes a 300 km
  thick layer of smog to build up.
• The smog, just like on Earth, forms when
  sunlight interacts with hydrocarbon molecules.

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Organic compounds from methane
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Titan What is Special?

• long streaks on surface, some 20 km wide
  (volcanic ridges?),
• underground ocean (water?, with extremophiles?),
  
• very smooth surface with few craters (young,
  with mushy layer?)

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Surface smooth with few craters

• long streaks on surface, some 20 km wide
  (volcanic ridges?),
• underground ocean (water?, with extremophiles?),
  
• very smooth surface with few craters (young,
  with mushy layer?)

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Titan Views

• This view of Titan's south polar region reveals
  an intriguing dark feature that may be the site
  of a past or present lake of liquid hydrocarbons.
  
• A red cross below center in the scene marks the
  pole.
• The brightest features seen here are methane
  clouds.

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Hubble Telescope - Surface Reconstruction
From October 4 to 18, 1994, the Hubble Space
Telescope Planetary Camera took 53 images of
Titan at wavelengths ranging from the ultraviolet
to the near-infrared. Fourteen of those images
have been used to make the first albedo map of
Titan's surface
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Titan Views
artists conception of surface of Titan rocky
surface imaged from Huygens lander
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