QUESTION:
Assuming that the barnacles seen on "Barnacle Bill" are shelters constructed
by some life-form for protection from the sun's radiation, I would expect
that they would be oriented so that the sun does not shine directly into the
opening.  Is there any indication that these formations are oriented in this
way, rather that having openings turned in no particular direction?

ANSWER from Jack Farmer on October 3, 1997:
Barnacle Bill was an unfortunate name choice for the first rock analyzed by
the Sojourner rover. The name was selected merely because the surface looks
to have a rough surface from a distance, like the hull of a barnacle
encrusted boat. The name was not meant to imply any sort of biology,
however. The rough surface of the rock is unlikely to be due to life, at
least life as we know it. First, there is no liquid water available to
sustain life, and the highly oxidizing nature of the soil and the high UV
flux makes this a highly inclement environment, any way you look at the
problem.

There are, however, far better explanations for the rock that have nothing
to do with life. The rough texture of the rock is more likely to be due to
differential weathering, where more resistant areas of the rock weathered
more slowly and now stand out in relief. Unfortunately, we were not really
able to get a close-up image of the rock surface with Sojourner, so we don't
know for sure the origin of the surface roughness.

But, the most significant thing about the rock is not its texture, but its
composition. It has a lot of silica (SiO2) compared to the other rocks we
have looked at from Mars. This indicates some kind of differentiation
process to enrich the rock in this compound. There are many potential
processes that can lead to silica enrichment, and at this point we are
simply unsure what process was involved with the formation of Barnacle Bill.
Perhaps the ongoing analysis of the Pathfinder data will provide additional
clues.

In terms of a preferred orientation of the knobby surface structures, they
do appear to be elongated in one direction, at least from the long distance
views provided by the Pathfinder camera. Potential mechanisms for the
elongation of the structures include: 1) (if the rock is igneous volcanic,
formed when molten rock material is erupted at the surface) flow of molten
lava before cooling could result in elongation of entrapped gas pockets
(vesicles) which would have been infilled later with secondary minerals
(perhaps silica?), 2) (if the rock is metamorphic, altered by heat and/or
pressure) it may have been squeezed by the pressure of deep burial, causing
the minerals to recrystallize in a preferred direction (perpendicular to the
axis of least stress), with lower temperature, silica-rich minerals forming
during the metamorphism, 3) (if the rock is impact ejecta) there may be a
preferred orientation because of fracturing and annealing (to form
silica-rich glass) in the rock due to elevated pressure and temperature of
impact (there are many impact craters in the region), 4) (if the rock is
sedimentary) the preferred orientation could be due to bedding formed when
the rock was originally deposited, which may have been enhanced by selective
cementation (silica cement) after burial.

Any of the above hypotheses is consistent with both the observed texture, as
well as the observed enrichment in silica.

In conclusion, based on available data, we have no evidence for biology in
any of the rocks or soils so far analyzed by Pathfinder. But this is not
surprising because it is unlikely that the instrumentation on the rover
could ever provide that type of evidence. This just means we need to return
to Mars with rovers outfitted specifically for the purpose of looking for
evidence of past (fossil) life in rocks. Then we need to select the best
samples (from the many available choices) to return to the Earth where we
can use more sophisticated methods to confirm or refute the hypothesis of
Martian life.

Jack Farmer