On the
Ars Technica website, there is a very detailed and lucid explanation
of NASA plans to search for life on Europa, a moon of the planet
Jupiter. The mission described is fascinating, but it may be a case
of people who want to spend 8 billion dollars to reassure themselves
that their dubious philosophical assumptions are correct. The
mission seems to be all about proving an “easy life” hypothesis,
one which seems to be very unlikely to be true from a purely
scientific standpoint.
Europa
is believed to be covered with a thick layer of ice, but it is
believed that deep below that ice is a watery ocean. The plan is to
land a robot probe on the icy surface of Europa. The probe will then
drill down into the ice, looking for signs of life. Advanced plans
for searching for life on Europa have always looked like the plan
shown in the NASA visual below. Under such plans a probe would release
something that drills down through the ice, and makes contact with
the ocean below.
The best way to search for life on Europa (credit: NASA)
When I
read the Ars Technica article, I was expecting to hear about a
mission such as this, one that would somehow make contact with
Europa's ocean underneath its ice. But the article did not describe
such a mission. It merely described a mission that would drill down a
little into the ice, and look for signs of life inside the ice.
There
are two reasons why such a mission seems like a gigantic boondoggle
that will almost certainly fail. The first and lesser reason is that
even if life had evolved in an ocean underneath Europa's thick icy
layer, it is unlikely that signs of such life would pass up all the
way through such a layer of ice. That ice is believed to be between
15 and 25 kilometers thick (10 to 15 miles thick). It seems unlikely that
any type of organism could survive a journey through such a thick
layer of ice.
The
second and better reason why such a mission seems very unlikely to
succeed is that the chance of life appearing in an ocean of Europa
seems extremely low. To calculate this chance, we must consider all
of the insanely improbable things that seemed to be required for life
to originate from non-life. It seems that to have even the most primitive life originate, you need
to have an “information explosion.” Even the most primitive
microorganism known to us seems to need a minimum of more than 200,000 base
pairs in its DNA (as discussed here).
Scientists
have been knocking their heads on the origin-of-life problem for
decades, and have made little progress. The origin of even the
simplest life seems to require fantastically improbable events.
Protein molecules have to be just-right to be functional. It has been
calculated that something like 1070 random trials
would be needed for a functional protein molecule to appear, and many
such protein molecules are needed for life to get started. And so
much more is also needed: cells, self-replicating molecules, a
genetic code that is an elaborate system of symbolic representations,
and also some fantastically improbable luck in regard to
homochirality.
Facts
such as these are troubling to those who believe in a random,
purposeless universe. To such people, it would be embarrassing to
have to concede that our planet seems to have been blessed by an
astonishingly improbable set of lucky events that got life started. So
such people often advance a kind of counter-thesis: what we may call
the idea of “easy life.” The “easy life” hypothesis maintains
that we didn't get lucky, because given the right ingredients and
chemicals, life will inevitably appear. Such thinking is
perhaps rather like the daughter's thinking in this conversation:
Mother:
Why are you leaving us and heading 2000 miles to Hollywood? The
chance of you becoming a star is one in a million.
Daughter:
No, it is inevitable that I will become the world's greatest
starlet.
When
you are faced with a mathematical reality that something that you
want to happen is very unlikely to happen, it is very effective
psychologically to “cross out” this troubling improbability by
maintaining that the thing is not unlikely at all, but instead has a
probability of 100%.
In the
case of the proposed Europa mission, we have a mission that we might
describe as “Desperately Seeking Easy Life.” Some people
pitching such a mission want very much for their “easy life”
hypothesis to be proven, and they are asking for 8 billion dollars of
taxpayer funds so that they can achieve this metaphysical
reassurance, and say to themselves, “I'm so relieved –
Earth wasn't so lucky!” It's basically the kind of “give me
lots of money so I can be reassured about my assumptions” thing
that would go on if a fundamentalist group were to ask for millions
of taxpayer dollars to fund projects digging underground looking for
Noah's ark.
Looking
at the probability of life arising by pure chance in Europa's ocean,
a purely chemical and biological assessment must rate the probability
as being extremely low. Now it is true that there may have been some
additional factor involved in the origin of life on Earth. Perhaps
life got started here through the action of some divine being or the
action of extraterrestrial visitors. But while such a higher power
may have acted to spur the start of life on many planets in our
galaxy, the chance of such a higher power working to create life in
some buried ocean underneath 20 kilometers of ice seems much smaller.
So even if we throw in the possibility of some additional power
helping life appear in our galaxy, it still seems unlikely that life
would exist in Europa's ice-buried ocean, given all of the
fantastically improbable things that have to happen for life to
appear from non-life.
The
proposed Europa mission seems like a fantastically expensive “shot
in the dark” that is very unlikely to succeed. Even if some hint of
life were to appear, it might well be some ambiguous signal like the
one produced by the 1976 Viking mission to Mars. A mission putting cameras
down into Europa's ocean might conceivably yield fascinating footage
of swimming creatures. But a mission drilling only a little into the
ice (like the currently proposed mission) would merely yield
some numerical data that might be of interest only to scientists.
Such data probably would still be subject to debate, and would be
unlikely to give a final decisive answer as to whether life exists on
Europa.
We
don't need the Europa mission because there are other ongoing
scientific research programs that can be used to test the “easy
life” hypothesis. One such program is the search for radio signals
from extraterrestrial civilizations, with a price tag a tiny fraction
of the proposed Europa mission. If the “easy life” hypothesis is
true, we would expect such searches to be successful before long.
(Their failure so far despite thousands of hours of searching time
may be a strong indication that the “easy life” hypothesis is not
correct.)
Another
such program is the search for atmospheric signs of life from planets revolving
around distant stars. If the origin of life is easy, and life is all
over the galaxy, we can expect that soon our space instruments will
start showing up by-products of life (such as abundant oxygen) in the
atmospheres of extrasolar planets.
So an
advocate of the “easy life” hypothesis cannot claim that the
Europa mission is essential to test such a hypothesis, as the
hypothesis will be tested by other programs searching outside of our
solar system.
Postscript: The selling point constantly made for SETI outside of our solar system is: there are so many planets where life might have appeared, so eventually we'll find something. But that argument cannot be used whenever you are talking about searching for life on one particular moon or planet. Think of it this way. Investing in some telescopic search of many stars (or a radio search of many stars) is like buying two big stacks of lottery tickets. But sending a robot mission to look for life on one moon or planet is like buying a single lottery ticket, and just as unlikely to pay off. 8 billion dollars is way too high to pay for a lottery ticket.
Postscript: The selling point constantly made for SETI outside of our solar system is: there are so many planets where life might have appeared, so eventually we'll find something. But that argument cannot be used whenever you are talking about searching for life on one particular moon or planet. Think of it this way. Investing in some telescopic search of many stars (or a radio search of many stars) is like buying two big stacks of lottery tickets. But sending a robot mission to look for life on one moon or planet is like buying a single lottery ticket, and just as unlikely to pay off. 8 billion dollars is way too high to pay for a lottery ticket.
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