by Carl Sagan
Last Updated February 1997
from Chance Website
Our knowledge of the solar system has been decisively
rewritten. Our species has visited what is now the outermost known
planet. Voyager's place in human history is secure.
If all goes well, it will explore, in much greater
detail than Voyager, multicolored Jupiter, its four large moons - one with active volcanoes, another with a possible underground ocean
- and its vast magnetic field; Galileo will also drop a scientific
probe directly into the atmosphere of Jupiter and radio back what it
finds. It is a trailblazing mission.
It is scheduled to begin operations
there in late 1995. While it's careening past worlds, Galileo will
be gathering data - about Venus, about the Moon, about two worldlets named
Gaspra and Ida, about the interplanetary gas...
and about the Earth. It will help determine the worldwide
distribution of greenhouse gases, the present status of the ominous
hole in the ozone layer over Antarctica, and the water content of
the upper atmosphere - central for understanding the ozone problem.
Furthermore, its investigations of the atmospheres of Venus and
Jupiter promise to improve our knowledge of our own fragile envelope
of air. Galileo will not only be exploring other worlds; it will
help us to understand and safeguard this world. Galileo is a worthy
successor to Voyager.
A lawsuit has been filed in Federal
District Court in Washington, D.C. - by the Washington-based
religious affiliated Christic Institute and other organizations - to
stop the Galileo launch on the grounds that it may pose a serious
danger to public health. Meanwhile, the White House, after
considering the dangers, has given the go-ahead for launch.
Concern about the environment and, especially, about the threat of nuclear war has been a thread woven through my life. I was a member of the team that discovered nuclear winter; I've twice been arrested at the Nevada Nuclear Test Site for demonstrating against continued American testing of nuclear weapons in the face of the Soviet unilateral moratorium; I opposed Ronald Reagan's Star Wars scheme from the moment he proposed it - on grounds that are now widely accepted; for the past decade I've been speaking out around the world to warn about greenhouse warming and depletion of the ozone layer.
At the very least, you can't charge me
with uncritical acceptance of high technology. Twenty years ago, I
also played a role in the NASA decisions to quarantine astronauts
returning from the Moon against the unlikely contingency that they
might bring back disease microorganisms. It turned out as we had
expected: there was not a trace of pathogens. But we had to balance
the low probability of their existence against the enormous
conceivable public health danger that might follow had we been wrong
and such bugs did exist. I would do the same today.
The authoritative Handbook of Physics and Chemistry in its various editions calls plutonium "a very dangerous radiological hazard" and "one of the most dangerous poisons known."
Robert Oppenheimer, the Director of the Manhattan Project, reminisced in February 1960:
A microgram of the stuff - a particle much too tiny to see - if breathed into your lungs may, over a period of decades, give you cancer.
Since Galileo carries 50 pounds of plutonium into space, it is hypothetically carrying a cancer fatality for everyone on Earth. This is an impossibility in fact, because it requires the plutonium to be funneled directly into the lungs of everyone on Earth, instead of being dispersed in and diluted by the Earth's atmosphere. But this is where much of the concern (including real anguish in many letters I've received) is focused. Understandably.
Why didn't we hear similar concerns voiced about the launch of Voyager or Viking (which also carried RTG's)? Because that was in another epoch - before Chernobyl, before Challenger, before the revelations about Rocky Flats, before we got serious about protecting the planet. One year before the Chernobyl disaster a Soviet Deputy Minister of the power industry announced that Soviet engineers were confident that you'd have to wait 100,000 years before the Chernobyl fission reactor had a serious accident.
Less than a year before the Challenger explosion, NASA spokesmen and contractor personnel assured us that at the then current rate of launch, you'd have to wait ten thousand years before a catastrophic launch failure. Hundreds of FBI agents descending on the Department of Energy's Rocky Flats facility in Colorado has raised justifiable fears of criminal carelessness by the U.S. government where public health and nuclear energy intersect.
The Department of Energy and the
Department of Defense have systematically minimized the dangers of
nuclear power and of nuclear weapons. These cases rouse valid
skepticism about government-sponsored probability estimates which
are intended to calm the public. Skepticism about government
credibility is, in my view, healthy. You can't maintain a democracy
without it. I'd like to see much more of it.
Are there any plausible circumstances in which
this could happen?
What if the trajectory is a little bit off and it hits the Earth?
Then, entering the Earth's atmosphere at 30,000 miles per hour, it might burn up; it's not guaranteed, it may even be unlikely, but there's a chance that all 50 pounds of plutonium would be vaporized. Some of the plutonium would quickly settle out; some of it would be carried widely by the winds and the general circulation of the Earth's atmosphere. It would be enormously diluted in the air.
Some people would breathe in more plutonium and some less over the next 50 years, but no one is likely to get as much radiation from this source as in a single dental X-ray. But there's a tiny chance that you can get cancer from such an X-ray. In our ignorance, we don't know what these low radiation doses would do. In the worst case, you might have an incremental chance of around one in 10 million of getting cancer were all of Galileo's plutonium to vaporize in the upper air. That's the equivalent of producing bone and other cancers in roughly a thousand people worldwide.
Or there might be no health effects at
all. We simply don't know. (Remember, these people are at risk only
if, improbably, Galileo burns up in the Earth's atmosphere on its
way back from Venus.)
Roughly 1000 deaths, over 50 years, in a world population that will by then be 10 billion people, seems very small. But if anyone dear to me is one of those people, I no longer find the odds comfortably small.
So then I have to ask myself: why
should it matter whether it's someone dear to me? Shouldn't I have
the same concern for the health of everyone on Earth?
They are not made by the Department of Energy or NASA contractors, but by NASA's Jet Propulsion Laboratory (JPL), run by the California Institute of Technology.
These are the people responsible for Voyager and most other American robotic missions to the planets, the people with the most experience on Earth in interplanetary navigation and the inventors of the gravity assist.
program for containing the plutonium in the Galileo RTG's and for
understanding the risks has cost NASA about S50 million.
When the JPL engineers add up all
conceivable sources of trajectory error and their probabilities,
plus the likelihood that the error will make the spacecraft hit the
Earth rather than miss it by a bigger distance, plus the probability
that simultaneously the spacecraft will be unresponsive to commands
from the Earth, they derive an overall estimate of the probability
of accidental impact. This number is 1 chance in 2 million.
This is somewhere around my threshold.
That's why I find the Galileo decision so agonizing. But taking
account of the past history of government incompetence or worse in
matters of public health, considering the likely scientific findings
(including the possibility that many more lives might be saved
because of Galileo's findings), and evaluating the low magnitude of
the risk, my personal vote is to launch.
So no protective covering was included to minimize the plutonium dispersal. No official thought seems to have been given to the possibility that it might be a bad idea to distribute deadly plutonium all over the planet. An even more serious danger than RTG's is power reactors - in which nuclear fission is occurring in Earth orbit. The chief offender here has been the Soviet Union, especially its radar satellites designed to follow the activities of U.S. warships worldwide. Their failed Cosmos 954 satellite distributed plutonium pellets all over Western Canada.
The Washington-based Federation of American Scientists (FAS), the Moscow-based Soviet Scientists Against War and the Nuclear Threat, and House bill H.R. 966, introduced this year, all propose, in the words of the House bill, a,
The FAS, the Chairman
of the Soviet group, and Rep. George Brown, sponsor of the House
Bill, unanimously support the launch of Galileo.
I would like to urge everyone concerned
about the Galileo RTG - including the scientists, engineers and
government officials who for the first time have been forced to
think seriously about this matter because of public protest - to
devote a proportionate amount of passion, wisdom and hard work to
those activities (and inactivities) that really jeopardize the human