鈥淲anted: Planetary Protection Officer. Responsibilities to include
safeguarding the health and safety of the Solar System. Primary duty to ensure
returning spacecraft do not infect Earth with alien life forms. Please apply to
NASA, stating experience and current salary . . .鈥�
There was a time when the job of PPO鈥攜es, such a position really does
exist鈥攚as considered a bit of a joke. After all, the Moon is the only
celestial body that spacecraft have visited and come back from, and the Moon is
so notoriously inhospitable to life that nobody really needed to worry that Neil
Armstrong and his buddies were going to bring back Moon bugs on the soles of
their space boots. But today鈥檚 PPO, one John Rummel, is taken far more
seriously. That鈥檚 because in 2008 NASA intends to bring back roughly 1 kilogram
of rock from Mars.
With an average global temperature of 鈥�55 掳C, Mars is not exactly a
tropical paradise. True, its surface is short on atmosphere and long on
potentially life-threatening radiation. But below the surface conditions may be
far cosier. There are signs of recent volcanic activity that could provide
geothermal energy for growth, and there may even be liquid water somewhere deep
down. In light of those possibilities, in 1997 a National Academy of Sciences
report concluded that there is a real, if remote, possibility that rocks brought
home from Mars will contain infectious microbes that鈥攕hould they get
loose鈥攎ight just devastate the Earth.
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It鈥檚 Rummel鈥檚 job to stop that taking place. Based at NASA鈥檚 headquarters in
Washington DC, Rummel can rely on numerous committees and working groups for
advice, and teams of engineers and scientists to put those recommendations into
practice. But if Martian microbes do end up taking over the Earth, it will be
down to him to explain what went wrong.
The plans for collecting Martian rock are already well under way (although
Rummel stresses that the details are subject to change). In 2003 and again in
2005, NASA will team up with the Italian and French space agencies to send a
spacecraft on the seven to eleven month journey to Mars. Once there, each craft
will deploy a lander fitted with a variety of gadgets to gouge out pieces of
rock to a depth of 1 metre below the surface.
On the back of each lander will sit a rocket鈥攁 Mars Ascent Vehicle. And
once the rock has been collected, the nose cone of each vehicle, will snap apart
like a giant piece of Tupperware to reveal two halves of a grapefruit-sized
container-cum-radio-beacon. The two halves will be embedded into each half of
the nose cone so that their exterior is protected from contamination by the Mars
atmosphere. When the rock is safe in the grapefruit, the nose cone will snap
shut.
The mission rests on these grapefruits, the only pieces of hardware to travel
from the surface of Mars back to Earth. Though the details have yet to be
finalised, they will be made from a highly tough combination of aluminium,
titanium, Teflon or steel. One thing is certain, however: NASA鈥檚 engineers will
have to find an ultra-secure way of sealing them.
One option is to fit the lids snugly into the bases and then detonate a
ribbon of explosives that would smash the two layers of metal together. Tests
show that this technique is ultra-reliable. 鈥淲e haven鈥檛 got it to fail yet. The
seal doesn鈥檛 allow any detectable helium leak, which is what we need,鈥� says Mark
Adler, chief engineer for the Mars Sample Return mission at NASA鈥檚 Jet
Propulsion Laboratory in Pasadena. Such pressure welding would also sterilise
the joint. Still, explosions are violent and could damage other bits of the
equipment, so NASA engineers are exploring other ways of sealing the
grapefruits, using simple mechanical compression, for example.
Once the containers have been successfully sealed, the Mars Ascent Vehicles
will lift off from the back of the lander, and release the grapefruits into
orbit between 400 and 700 kilometres from the Martian surface. Solar panels on
the grapefruits will activate the radio beacons to tell the Return Orbiter,
which will be sent on the 2005 launch, they want a lift home.
The Return Orbiter will scoop up the grapefruits and load them into the two
Earth Entry Vehicles it carries on its back. If everything goes to plan, the
only part of the package that has been in contact with Mars will be tucked
inside the grapefruits. Still the 25-kilogram Earth Entry Vehicles will hit the
ground at around 144 kilometres an hour鈥斺�漣t鈥檚 a bad car crash,鈥� says
Adler鈥攕o the engineering crew needs to make sure they do not burst open.
For those reasons, they are considering another layer of crushable packing
inside the Earth Entry Vehicles to act as a sort of crumple zone. 鈥淲e are going
to have to convince a lot of people that this works,鈥� says Adler鈥攊ncluding
perhaps the US President, who may have to authorise the project before it is
permitted to fly.
When the Earth Entry Vehicles have landed (probably somewhere in Utah), the
Martian rock and whatever life forms it carries will be rushed to a
high-security containment lab, similar to those used to handle the most deadly
organisms, such as Ebola. There, exobiologists will search for telltale signs of
life, such as cell walls and membranes, and a preponderance of right-handed or
left-handed molecules (biological catalysts tend to favour one form over the
other). They may even be surprised by something more subtle鈥攁 build-up of
chemicals that cannot be explained by any known physical or chemical process,
for instance.
So what are the chances that the grapefruits will contain Martian microbes
that鈥攕hould they escape鈥攚ould spread like dandelions, drop humans
like flies, exterminate all the fish in the sea, and decimate the world鈥檚 crops?
Vanishingly small, says Rummel. Martian microbes, assuming they even exist, will
have evolved in the total absence of all Earthly life forms, so they probably
won鈥檛 have the wherewithal to infect them.
Well then how about Martian bugs that chase our microorganisms out of their
current niches, irreversibly disturbing the delicate food chains that make
diverse life on Earth possible? Also unlikely, says Rummel, ever the killjoy.
Only the dry valleys of the Antarctic bear a resemblance to Mars, and it鈥檚 a
slim resemblance at best, so Martian microorganisms are likely to be far less
well adapted to the Earth than its resident bacteria.
But that doesn鈥檛 mean that Rummel isn鈥檛 haunted by his own private
nightmares鈥攍ike the one where the astrobiologists find that their newly
discovered 鈥淢artians鈥� are just terrestrial bacteria that have taken a trip to
Mars and back. 鈥淲hat is the worse case scenario?鈥� asks Rummel. 鈥淭hat all we find
in the sample is contamination from Earth.鈥�
To stop that happening, and because good interplanetary manners dictate that
you don鈥檛 go around infecting other planets, NASA鈥檚 engineers and scientists
also have to find a way to dissuade Earth bugs from hitching a lift to Mars.
As a marker of overall cleanliness, anything that lands on Mars must carry
with it fewer than 300 000 viable aerobic bacterial spores, the ones that need
oxygen before they can spring to life. 鈥淗alf a bottle of water would typically
contain more spores,鈥� says Rummel. The standards will be far more stringent for
the Mars Sample Return missions.
The Viking lander, the first spacecraft to land successfully on the surface
of Mars (the Soviets attempted several landings beforehand, but none worked
out), carried fewer than 30 aerobic spores. The Viking lander was encased in a
鈥渂ioshield鈥� and cooked in a giant oven, before being loaded on to a Titan
rocket. The bioshield was jettisoned on the way to Mars, revealing a squeaky
clean lander. Cost restraints and newer, fragile technologies, such as
electronic chips, mean that some parts of the Mars Sample Return landers won鈥檛
be able to handle extreme temperatures. So NASA scientists are testing
alternative ways of sterilising the landers and grapefruits, including
ultraviolet irradiation, high pressure hydrogen peroxide solutions, and oxygen plasmas.
Of course, sterility isn鈥檛 everything; the spacecraft and grapefruits must
also be clean because even the remains of dead terrestrial microorganisms could
mislead astrobiologists searching for signs of life in the Mars rock. 鈥淣o one
has ever cleaned anything as bulky and as big as a spacecraft to this level,鈥�
says David White, a microbial ecologist from the University of Tennessee in
Knoxville, who is helping NASA with this mighty cleaning job. 鈥淎nd we don鈥檛 yet
know whether we can do it.鈥� One back-up strategy is to chemically label
bacterial remnants from Earth so that they can be distinguished from any Martian
bugs when the spacecraft returns.
Of course, all this fuss raises the question of whether it鈥檚 worth it just to
bring to Earth what will probably turn out to be a lifeless hunk of rock. But
lifeless or not, that hunk of rock could help to address some key questions.
Does its crust contain much sedimentary rock, for example? Water often plays a
role in the formation of these rocks, so finding them could speak volumes about
the history of water on Mars. In addition, sedimentary rocks are far more likely
to contain fossils than the igneous rocks from the Martian meteorites found here
on Earth. 鈥淚t鈥檚 a brand new world that has to be discovered and understood,鈥�
says Carl Agee, chief scientist for astromaterials at the Johnson Space Center
in Houston. 鈥淭hat鈥檚 what makes geologists so excited.鈥� It also raises the pulse
rate of the average biologist because an intimate knowledge of Mars geology is a
prerequisite for answering the big one: Was there ever life on Mars, and if it鈥檚
still there, where is it?
鈥淭he first order of business is to characterise the planet and find the
habitats, because until we understand the habitats it鈥檚 presumptuous to go
looking for life,鈥� says Rummel. Meanwhile, he adds, 鈥淲e are checking for signs
of life in the return samples just as a precaution.鈥�
Well, the chances of anything coming from Mars may be very slim, John. But
speaking for the natives of planet Earth, all I can say is we鈥檙e glad you鈥檙e on
the job.