Monday, July 6, 2009

Do we need “All of the Planets, All of the Time”?

A colleague of mine with whom I have written a paper or two, Andrew Schuerger, announced at LPSC one year the existence of life on Mars. While it was a little tongue-in-cheek, his point contained an essential truth: that given the decontamination procedures in use, viable microbial life had almost certainly been transported to Mars on the inside of spacecraft. This was not idle speculation, nor was it entirely novel; cameras retrieved by the Apollo astronauts from the Ranger Lunar Landers still carried culturable bacteria after years of exposure to vacuum and radiation on the surface of the moon.

Even so, this doesn’t mean that we can expect to see carpets of green radiating out from our landed spacecraft any time soon. In fact, what organism are present are most likely in the form of dormant and hardened spores since Mars remains a pretty harsh place for even bacteria to grow. Further, anything viable on the exterior of a Martian spacecraft or on the surface would be killed within at most a few months of exposure to UV, depending on where it fell (you can take a look at http://adsabs.harvard.edu/abs/2007Icar..192..417M for more details on these extreme cases).

This begs the question as to whether procedures used to decontaminate spacecraft and prevent forward contamination (not to be confused with reverse contamination by any extraterrestrial microbes, the type popularized by movies like the Andromeda Strain), collectively known as planetary protection and administered out of the Planetary Protection office of NASA in the United States, are really necessary.

One reason for wanting extra stringent sterilization is scientific. You need to have a very clean spacecraft to prevent any sensitive life or organic-detection equipment from inadvertently showing a false positive. To prevent this, severe decontamination measures are often taken. For instance, the Robotic Arm on the Phoenix Lander was enshrouded in a “bio-barrier” until after landing. But as we didn’t want to come to Mars to “discover” terrestrial organics on the scoop, this was an important precaution.

The specific level of sterility required varies by destination. The Robotic Arm employed by Phoenix needed to be as clean as it was as a result of its potential contact with the ice table in a region where life or its traces were possible. By international agreement, COSPAR has designated four levels of these regions which require progressively more stringent planetary protection measures (category five relates to reverse contamination http://cosparhq.cnes.fr/Scistr/Pppolicy.htm). The level of protection ranges from none, for a level one body like the moon to full sterilization for access to so-called special regions of Mars or Europa, the only two level four bodies in the solar system.

There are a few locations that may come as a surprise. Even orbiters of Mars are designated as level three, while a Venusian lander is rated at level one, mainly because there is nothing we can do to a spacecraft on Earth that is as destructive as what the venusian environment will do in-situ.

Either way, exploring a special region can be a costly or even a prohibitive burden on any space mission. Sterilization for the Viking Mission cost almost US$320 million, adjusted for inflation, or about 70% of the cost of an entire discovery-class mission.

More significant is the potential impact on mission operations. Often there are financial pressures which require reducing the functionality of hardware, a process known as descoping. This is true of nearly any mission, large or small. Cassini, a burly flagship, had its scan platforms eliminated while Phoenix, a bare-bones Scout, saw its Direct-To-Earth antenna and descent imager descoped. Thus, as a significant expense, one can cut costs dramatically by avoiding any region that requires special procedures altogether.

This is having a large impact on our exploration of Mars. Both ESA’s Exo-Mars and NASA’s Mars Science Lab, each a flagship-class mission, are avoiding special regions to pare back costs.

As well, it is arguable that an opportunity to study Europa might have been lost by the requirement of disposing of the Galileo Spacecraft in Jupiter’s atmosphere and not having it strike Europa. This could have been observed from the ground, or timed to coincide with the passage of the New Horizons spacecraft, which passed through the Jovian system on a gravity assist in February, 2007. The resulting plume could have told us a great deal about the composition of the Europan surface. Even if it had not been placed on a collision course for the moon, the spacecraft could have continued collecting data until it ran out of orbit-maintenance propellant and allowed to become derelict.

It is true that we do not want to contaminate these places to the point that we can no longer study them. But what makes these regions special is also what makes them interesting and desirable targets. As such, I have to wonder if the best is not the enemy of the good in this case. As much as we can learn incrementally from non-special regions, the rewards of exploring these other areas are potentially much greater. Space exploration is a public enterprise, and nothing grabs the imagination of our funding base more then uncovering more about the potential for life in the solar system and our place in it. If we continue to ignore these places because we set such a high bar for their exploration, we risk loosing this valuable support.

Perhaps we should be thinking in terms of resource management. Anyone who has had a cold can appreciate the resourcefulness of the little Von Neuman machines which are terrestrial microorganisms. But evolution cannot operate in the absence of reproduction and even in special regions, conditions are not exactly clement. The chances of terrestrial contaminants merely venturing beyond the level of dormant spores, not to mention thriving and replicating, anywhere on the Martian or Europan surface is low.

As such, perhaps we could consider setting aside areas where limited local contamination is permissible. This would preserve the special regions as a whole while allowing us to get answers to our biggest outstanding questions. As well, recall that any directly interacting part or life detection sensor will need to be incredibly clean to avoid false positives, so even this compromise does not increase the risk much. As Andrew has said, there is life on Mars within our landed spacecraft. But if it is confined to that barest of inhabitable niches, then the planet remains protected.

Either way, the point may be moot soon. With boots-on-the-ground human exploration planned for not long after the current pair of missions to Mars, contamination becomes inevitable. After all, it’s hard to sterilize a creature that is 10% by mass bacteria.

For more information, you can check out this helpful Nature News article: http://www.nature.com/news/2009/090520/full/459308a.html

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