- Quarantines can help a society protect
itself from dangerous infections.
-
- The word comes from the French, for the
40 days of isolation once faced by new arrivals who may have been infected.
After the quarantine has passed, they were either certified to be disease-free
- or dead.
-
- Quarantining an entire planet against
potentially harmful extraterrestrial diseases becomes more difficult.
-
- Though the odds are minuscule, what,s
needed to prevent something with global consequences? What protections
are reasonable?
-
- The launch of Stardust to retrieve a
milligram of dust from the Wild-2 comet is the first human attempt to bring
back extraterrestrial samples in almost three decades.
-
- NASA would like to bring back samples
from Mars in less than 10 years. Other comet missions are also on tap,
and the Russians dream of retrieving samples from the Martian moons Phobos
and Deimos.
-
- Space Spores
-
- There's also the renewed debate over
natural transport, via meteorites and space dust.
-
- A century ago, scientists used the term
'panspermia' to describe the possibility that spores could naturally pass
from planet to planet. Today, space experts have asked themselves if the
quarantine issue isn't already moot, since new evidence and computer simulations
suggest there never has been biological isolation between planets.
-
- Asteroid impacts on Earth, the moon and
Mars have flung rocks off each world, circling the sun until they slam
into a nearby world.
-
- One extreme view is that life on Earth
is the result of contamination from Mars. That smaller planet cooled earlier
than Earth, and seems to have had oceans for hundreds of millions of years
while Earth's surface was still molten.
-
- Martian rocks bearing spores could have
rained upon Earth until our oceans formed and provided a hospitable environment
for a few lucky survivors.
-
- Rain From Mars
-
- Even today, a hundred tons of meteorites
and space dust fall on Earth every day. About one-tenth of 1 percent of
that - perhaps 100 kilograms per day - is from Mars. Four billion years
ago, during what planetary scientists call the Period of Heavy Bombardment,
there would have been much, much more.
-
- But could microorganisms survive these
interplanetary journeys?
-
- During a conference on Mars exploration
in Boulder, Colo., last August, retired Swedish industrialist Curt Mileikowsky
discussed the work of a European team that evaluated exactly these prospects.
The group considered hazards such as shock and heating during ejection
off the planet's surface, cosmic rays and heat-induced DNA decay while
en route, and heating during impact at the end of the journey.
-
- For some meteorites, the Europeans were
astonished to discover that microbial survival rates could be very high
even for trips that lasted up to a million years.
-
- While it's commonly thought that meteorites
falling to Earth are thoroughly seared by the heat of atmospheric entry,
this is a misconception. The outer skin may be burned off during the very
brief fireball phase, but most of the meteorite's interior remains at the
subfreezing temperature of deep space.
-
- Freshly fallen meteorites, far from being
red hot, often have frost on them from condensation. Any microbial passengers
would have a gentle landing.
-
- Hazards From Related Life
-
- If ancient Mars life also left modern
descendants at home, the biohazard to its cousins on Earth is much higher
than that from two independent strands of life. In a 1994 article entitled
'Is It Dangerous To Return Samples From Mars To Earth?,' Carl Sagan wrote:
"If putative Martian organisms were originally transferred to Mars
by collisions with the Earth, they may be enough like us that they could
be pathogenic." The same argument holds if the transfer was from Mars
to Earth. Whether Mars had - or has - life that's related to Earth life,
some sort of quarantine is called for. NASA has implemented some protocols
for its Mars samples, but the issue includes more than just that planet.
Last year, the National Research Council in Washington, D.C., issued a
report on the 'biological potential' for samples from other solar system
bodies, and concluded that while some sources could be judged entirely
nonhazardous, others - including comets - still require protective measures.
-
- Shttp://www.abcnews.go.com/sections/science/DailyNews/pace
Sterilization
-
- Stardust scientists insist that their
collecting - high-speed impact of cometary dust grains into the fine aerogel
collectors - will automatically sterilize the recovered material. Test
results back this up - at least for what we keep calling 'life as we know
it.'
-
- Some scientists remain unconvinced that
current protections are good enough.
-
- A new group called the International
Committee Against Mars Sample Return recently launched a Web site discussing
its concerns, with links to other documents on planetary quarantine.
-
- Barry DiGregorio, co-founder of the group,
says he's concerned that NASA may relax its standards of Mars samples.
One idea even described a special-purpose space station designed to process
extraterrestrial samples in absolute isolation from Earth's biosphere -
a quarantine for the Space Age.
-
- James Oberg spent 22 years as a rocket
scientist for NASA, and has written eight books and numerous articles
on space flight.
-
- Life on the Moon, Maybe
-
- It's commonly thought that on at least
one occasion, infectious germs were brought back from the moon.
-
- This occurred on the Apollo 12 mission
in November 1969, when the crew retrieved pieces of the Surveyor 3 robot
that had been on the moon for two years. Subsequent culturing of swabs
from various locations gave one positive result - viable Streptococcus
mitus spores were picked up from a swab rubbed inside the Surveyor's camera
case.
-
- Microbiologists weren't all that startled
by the finding, since the temperatures inside the hardware on the lunar
surface had stayed well within the range that microbial spores were known
to tolerate, even if it had also been in a vacuum (and viable spores have
been retrieved from spacecraft brought back after months or even years
in Earth orbit).
-
- Unfortunately, the technician collecting
the lunar swabs back in 1969 was seen to violate isolation protocol by
laying the new swabs down on a non-sterilized table surface. So the positive
results could have been caused by somebody sneezing in the room the previous
day.
-
- Even though it's intriguing that the
one positive was the sample taken from the most sheltered interior location
of the hardware, the finding must be chalked up as interesting if true,
and left to dangle in perpetual ambiguity.
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