Alien Infection

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Alien Infection

 

Astrobiology Magazine

http://66.242.35.139/news/item.php?keyid=5635 & page=1 & category=1

 

August 28, 2003

 

Alien Infection

 

By: Leslie Mullen

 

 

When diseases cross the species barrier and infect humans, they dominate

news headlines. Just imagine, then, the reaction if potentially infectious

pathogens were found in rock samples from Mars.

Credit: NASA

 

When diseases like SARS, Mad Cow Disease and Monkeypox cross the species

barrier and infect humans, they dominate news headlines. Just imagine, then,

the reaction if potentially infectious pathogens were found in rock samples

from Mars.

 

As we look toward exploring other worlds, and perhaps even bringing samples

back to Earth for testing, astrobiologists have to wonder: could alien

pathogens cross the " planet " barrier and wreak havoc on our world?

 

Even though there is no proof of bacterial or viral pathogens anywhere

except Earth, there is already a worried advocacy group called the

International Committee Against Martian Sample Return, and science fiction

novels like " The Andromeda Strain " depict nightmare alien infection

scenarios. The possibility of cross-planetary contamination has concerned

NASA since the early days of the Apollo program, so, as a precaution, the

astronauts were quarantined for three weeks after they left the moon.

 

Chris Chyba, who holds the Carl Sagan Chair for the Study of Life in the

Universe at the SETI Institute, says there are two types of potential alien

pathogens: toxic and infectious. Toxic pathogens act as a poison on other

organisms. Infectious pathogens are viruses or bacteria that are passed

between organisms, causing sickness.

 

Some viruses and microbes rely on specific biological systems in order to

replicate and infect their host, so not all pathogens affect all organisms

the same way. Chicken farmers, for instance, can remain untouched by a

disease that decimates their flocks. It could be that a martian microbe

would enter the human body, but is rendered harmless because it is

incompatible with human physiology.

 

" After living in the dirt of Mars, a pathogen could see our bodies as a

comparable host; they could treat us ´like dirt,´ " says John Rummel, NASA´s

Planetary Protection Officer. " But, to quote Donald Rumsfeld, we´re dealing

with the unknown unknowns. It could be that even if the microbes lived

inside us, they wouldn´t do anything, it would just be this lump living

inside you. "

 

 

" After living in the dirt of Mars, a pathogen could see our bodies as a

comparable host. " -John Rummel

Image Credit: SF Tomajczyk

 

The conditions on Mars are much different than those in the human body, so

an inert pathogen seems the most likely scenario -- especially since any

life on Mars would have evolved without humans being present. Co-evolution

is why some pathogens only affect certain organisms.

 

Infectious pathogens evolve based on the reactions of their hosts. As the

host develops defenses against a predatory pathogen, the pathogen has to

devise new means of sustaining itself within the host (or risk its own

extinction).

 

Some toxins also developed through co-evolution. As predatory organisms seek

food, their prey develop ever more sophisticated means to escape being

eaten. Many organisms developed specially targeted toxins as part of this

evolutionary arms battle.

 

Rummel says that humans have evolved a complex defense system to prevent us

from getting sick from a whole host of disease and pathogens. But

non-specific microbes - where human physiology did not influence their

evolution - may evade our defense mechanisms.

 

The best way to understand the spread of potential alien pathogens is to

examine the spread of such non-specific pathogens on Earth.

 

One example of a non-specific toxic pathogen is cyanobacteria that produce

hepatotoxins (toxins affecting the liver) and neurotoxins. According to

Chyba, cyanobacteria living in lakes on the alpine pastures of Switzerland

have been implicated in a hundred cattle poisonings over the past 25 years.

Chyba says the cyanobacteria most likely did not develop their toxins in

order to escape predation from cows (or to kill the cows in order to eat

them!).

 

" Rather, the susceptibility of cattle to these toxins seems simply to be an

unfortunate coincidence of a toxin working across a large evolutionary

distance, " Chyba writes.

 

 

An example of an infectious pathogen working across large evolutionary

distances is the bacterium Serratia marcescens.

Credit: Digital Learning Center for Microbial Ecology

 

An example of an infectious pathogen working across large evolutionary

distances is the bacterium Serratia marcescens. It is found in a variety of

animal species, and also can be found free-living in water and soil. Its

transmission from human sewage has resulted in the decimation of Caribbean

elkhorn coral.

 

" The distance between humans and corals emphasizes the possibility that

certain organisms may prove pathogenic across a wide evolutionary divide, "

Chyba writes.

 

Of course, the evolutionary divide between humans and coral would not be as

wide a gulf as between any martian organisms and human beings. Yet one

theory for the origin of life on Earth is that it was transferred here from

Mars by meteorites. This variant of the " Panspermia " theory suggests that

life on Earth and any life on Mars might be closely related.

 

If Mars and Earth share the basis for life, this life would presumably have

evolved well beyond the original form. Such a large evolutionary divide

could provide protection from infection. But it could also mean that if

infection does occur, it might be related closely enough to some Earth life

to blaze through that population unchecked.

 

Human infection is not the only concern of planetary protection. Life on

Earth forms an interconnected, highly dependent web, so a pathogen affecting

any life on Earth could have serious repercussions for the health and

environment of our planet.

 

Protecting the Earth is, of course, an international concern. The Committee

on Space Research (COSPAR) of the International Council on Science, through

consultation with the United Nations, makes recommendations to space-faring

nations on planetary protection policy. The United Nations Outer Space

Treaty of 1967 requires that the introduction of extraterrestrial materials

must not adversely alter the Earth´s environment.

 

The treaty also says that we must not contaminate other planets as we

explore outer space. Astrobiologists especially are concerned about

inadvertently transmitting microbes from Earth. Bacteria can endure the

cold, dry vacuum of space, so a long journey of months and even years may

not be sufficient to ensure spacecraft sterilization. Our search for life

elsewhere will be frustrated if we come across microbes on another planet,

only to later find that we were the ones who brought them there.

 

 

Bacteria can endure the cold, dry vacuum of space, so a long journey may not

be sufficient to ensure spacecraft sterilization.

Image Credit: Jeff Johnson

 

The previous Mars landers, from Projects Viking and Pathfinder, were

constructed and handled in clean environments to prevent Earth microbes from

hitching a ride to the Red Planet. The Mars Exploration Rovers " Spirit " and

" Opportunity " that currently are headed for Mars followed similar " clean

handling " guidelines.

 

The MER missions will not bring samples of Mars back to Earth, but future

mission proposals do include bringing samples back for testing. For

instance, one recent Mars scout proposal suggests collecting atmospheric

dust. The spacecraft would fly through the atmosphere, collect the dust, and

then sterilize the dust as it flies back to Earth.

 

This strategy follows the guidelines set by a 1997 US National Research

Council report, which said sample returns must be either contained or

sterilized.

 

" Sterilization might present a problem for some samples, but it is well

suited to atmospheric dust since you have a dry medium, " says Rummel.

" Sterilization involves heating, and that wouldn´t alter the dry dust much. "

 

Fearing that containment or sterilization will not be adequate for

protecting the Earth from potential pathogens in martian samples, some have

suggested that the International Space Station (ISS) should be used to study

samples. But Rummel doesn´t agree.

 

" A lot of time and resources are needed to keep the station where it is, but

what goes up must eventually come down, " says Rummel. " ISS has an orbital

life of decades, not hundred of thousands of years. Knowing that, we need to

ask if it is a good place to conduct biological research. "

 

" Containment is also a problem, since there´s not much space to work with, "

Rummel adds. " What do you do if a person on board is exposed? The Earth, on

the other hand, has ample space to deal with accidents, or to build a new

lab next door, if necessary. "

 

 

Japan´s MUSES-C spacecraft, launched May 2003, is headed for asteroid 1998

SF36.

Image Credit: ISAS

 

The only samples that have been returned to Earth so far have come from the

moon. Astronauts on the Apollo missions returned 379 kilograms (835 pounds)

of rock and soil from the Moon, and three Russian spacecraft (Luna 16, 20

and 24) also returned moon samples. The samples were kept in sealed

containers until they arrived at their respective laboratories for study.

 

Some might argue that the precautions of containment or sterilization are

not necessary, since samples from other celestial bodies have been falling

on Earth since its origin. Comets and asteroids are believed to have

impacted the Earth frequently in its earliest years, seeding the young

planet with water and organic chemicals.

 

In addition, many meteorites have been identified as originating from Mars.

A storm of controversy erupted when, in 1996, NASA researchers claimed to

have found fossilized life forms in the martian meteorite ALH 84001.

Although this claim is still hotly debated, some see it as evidence that

martian microbes already have arrived on our planet.

 

" There may indeed be a natural exchange of microbes between Earth and Mars, "

says Rummel. " But we´re being cautious, and we will apply the appropriate

controls. We can´t make the risk zero, but we can make it very small. That´s

the reason why space exploration is so important -- it allows us to start to

address the sorts of questions we are asking. "

What´s Next

According to Rummel, there are no set plans to bring a Mars sample back to

Earth. However, some proposals discuss having both the European Space Agency

and NASA launch martian sample return missions by 2011, with samples

returning to Earth by 2016.

 

Sample return missions currently in progress include spacecraft designed to

sample a comet, an asteroid, and the solar wind. Although life is not likely

to be found in these places, the precursor chemicals that make life possible

may be present.

 

NASA´s Stardust mission, launched in 1999, will reach comet Wild 2 in

January 2004. Stardust will return to Earth with both cometary and

interstellar dust particle samples in January 2006.

 

NASA´s Genesis mission was designed to collect solar wind samples. The

spacecraft was launched in August of 2001 and is now collecting particles

coming off the sun. The samples will be returned to Earth in September 2004.

 

Japan´s MUSES-C spacecraft, launched May 2003, is headed for asteroid 1998

SF36. After its arrival in June 2005, the spacecraft will gather up to one

gram of material from a variety of sites on the asteroid. The samples are

expected to arrive back on Earth by June 2007.