Pictures from Curiosity’s Mars mission are a welcome relief from our earthbound travails.

It’s no wonder media outlets hyperventilate at the mere thought of such reliably happy material.

But one important aspect of the mission is routinely overlooked in news coverage; and that is the role that plutonium has played in fueling Curiosity’s race through space.   The success of this mission ensures that more will be attempted using the same method of propulsion.  Therein lies the concern.

Nasa has been at great pains to downplay the risk posed by plutonium fuel, insisting that the pelletized fuel is “unlikely,”  even in case of an accident, to be released into the human environment:

It is manufactured in a ceramic form that does not become a significant health hazard unless it becomes broken into very fine pieces or vaporized and then inhaled or swallowed. Those people who might be exposed in a Mars Science Laboratory launch accident would receive an average dose of 5-10 millirem, equal to about a week of background radiation. The average American receives 360 millirem of radiation each year from natural sources, such as radon and cosmic rays.

When examined a little more closely, this argument fails to comfort.  The “360 millirems” cited by Nasa as every American’s dose from natural sources (so-called “background radiation”) refers to external radiation, and assumes that in case of an accident, human exposures to radiation would be limited to external, and therefore finite doses.  

However, the greatest danger from plutonium is posed by its effect when taken internally.  In which case it remains in the body indefinitely, constantly  bombarding surrounding cells with enormous destructive energy.  Even the tiniest possible particle of plutonium has devastating potential for the human body.

Internal exposure can result when plutonium “dust” becomes airborne following an accident that destroys the matrix in which has been captured, thus distributing it in such a way that it can be inhaled or absorbed into the food chain.

Witness the EPA’s take on the effects of plutonium:

External exposure to plutonium poses very little health risk, since plutonium isotopes emit alpha radiation, and almost no beta or gamma radiation. In contrast, internal exposure to plutonium is an extremely serious health hazard. It generally stays in the body for decades, exposing organs and tissues to radiation, and increasing the risk of cancer. Plutonium is also a toxic metal, and may cause damage to the kidneys.

Even though the EIS (Environmental Impact Statement) for the launch of Curiosity put the odds of a plutonium release from the overall mission at “one in 220,” as one concerned commenter observed:

The EIS says “overall” on the mission, the likelihood of plutonium being released is 1-in-220. It puts the odds at 1-in-420 of plutonium being released in a launch accident. This could “release material into the regional area defined…to be within…62 miles of the launch pad,” says the EIS. The most densely populated part of that area is Orlando.

When the overall record of rocket failures over the course of the race for space is considered, those odds don’t look particularly good to me.  If we are about to embark on a new era of space exploration amid the cost constraints  and privatization that is likely in the twenty-first century, there is genuine reason for concern should more and more deep space missions be fueled with plutonium rather than the solar arrays of the past.

I hate to poop on the parade, but as we celebrate the achievements of Curiosity shouldn’t we, also be wiping our brow with relief and reflecting that, this time, the worst did not happen?