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Life and Death are important on icy worlds. Life on icy worlds occurs in the
Solar System and probably throughout the Universe. Among them are Earth
(Antarctica, Snowball Earth) and probably one or more of the icy moons of
Jupiter (JIMs) and Saturn. These worlds provide the three things life
requires - the chemicals of life, energy to drive it, and
habitats to support it. Death also occurs on icy worlds resulting in
potential preservation of life forms and products as fossils that may have a
story of the origin and evolution of life on the icy world.
On Earth's current and past icy worlds, life abounded. It lives in close
association with ice-shelves and sea ice in the Antarctic and Arctic icy
worlds. There life lives easily in a wide variety of sub-ice, inter-ice, and
surficial ice habitats. Earth's fossil record shows that life endured
the Neoproterozoic Snowball Earth, covered entirely or substantially by ice.
Life was not eliminated and opportunities continued over tens of millions of
years for its existence. Life has no problem with ice.
The icy worlds of Earth provide analogues for others in the Solar System.
While evidence for life on Jupiter's or Saturn's icy moons is absent, the
inferred sub-ice oceans suggest that habitats for life could be abundant and
diverse. Life present there may not resemble any on Earth, but all life
requires resources that are heterogeneously distributed in habitats. These
resources may include energy, substrates, primary production, prey, shelter,
among others. Thus, a search strategy for icy worlds, Europa in particular,
is to define probable habitats by analogy with Earth's ice habitats (Table).
At least 13 habitats may exist, but most are not accessible at the surface. A
search strategy therefore must identify sites where the habitats have been
transported to and incorporated into the icy crust and exposed at the surface.
Death and the fate of the bodies or biochemicals, processes encapsulated in
the term taphonomy, then become important. Death, as ancient and modern
fossils of individuals, assemblages and biomarkers, is also likely to be
preserved on icy worlds through various taphonomic processes well known on
Earth in both icy and non-icy environments. These processes include
transportation of sub-ice habitats to the icy crust, extrusion of water into
or onto the icy crust, and freezing of ice habitats into the crust. The last
taphonomic stage is then the exposure of these preserved habitats at the
surface or near-surface of a moon or planet. Various geologic and glaciologic
processes, such as cracking, fissuring, melting, tilting, folding, and
faulting may expose the habitats where exploration is possible.
Taphonomic and biogeographic inferences based on current images of icy world
surfaces provide a search strategy for proposed future exploration of JIMs.
The exploration sites need to be identified through geologic study with
respect to habitat taphonomy, and then detailed imaging and analyses need to
be acquired of those sites from spacecraft carrying high resolution
instruments. A later exploration stage will be to contact the surface sites
with probes, impactors, penetrators, "ice clippers", and or rovers that
can search for both life and death on icy worlds
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