The Lessons of Exposure
An interview with Gerda Horneck
|Gerda Horneck of the German Aerospace Center
In this interview with Astrobiology Magazine, Gerda Horneck of the German Aerospace Center discusses the effects of space radiation on life. She has spent her career studying the controversial concept of Panspermia – that life could be transported between different planets by meteorites. She has also looked at issues faced by human astronauts as they venture into space and explore other worlds.
Astrobiology Magazine (AM): When did you start doing astrobiology research?
Gerda Horneck (GD): Nearly 40 years ago, when I earned my Ph.D. My supervisor wrote the first German book on the origin of life. He asked me in my examination, “If DNA could be transported from the Earth to another planet, would that be sufficient to start life?” That was the first time I was confronted with this type of question.
Since then, astrobiology has become very popular, and I think I have maybe contributed a little bit to that. I feel like somebody who spread seeds on a field, and for awhile the field was dry but then suddenly the rain came, and now all the plants are growing.
AM: You sent a lot of biology experiments up on the space shuttle, right?
GD: Yes. But I started with Apollo 16. We did radiation dosimetry, the biological effects of cosmic radiation. I also worked on Apollo 17, and the Apollo-Soyuz test project. Then there was a gap until SpaceLab 1, and then I worked with all the SpaceLab missions. I’ve also worked with Mir. But now we’re waiting, looking to when the Columbus facility is brought back up. They have ETP, the European Technological Platform, which is a big facility to house biological systems that will be exposed to space.
AM:What do your studies teach us about astrobiology?
GD: I was trained as a geneticist and radiation biologist, so I’ve always been interested in what radiation does to biology. On Earth, we have ionizing radiation and solar ultraviolet radiation. So we asked the question that, if we bring organisms and human beings into space, what does the radiation do?
This was 30 years ago. Back then, Panspermia was not a fashionable theory; nobody liked it. Only after the martian meteorites were found did we realize, oh, yeah, material can be transported between the planets. Then Imre Friedman detected endolithic organisms – microbes living inside rocks – and so the picture came together that it might be possible for living creatures to be transported between the different planets. Much of my research was spent on identifying the different steps that are necessary for the interplanetary transport of life. We did either simulation experiments or experiments in space to see under what conditions it could happen.
|Mars, our planetary neighbor
Credit: NASA/JPL Viking
Now, with our neighbor planet Mars being of so much interest, and so many missions going there, I’m again interested in the habitability of that planet, but again from the point of view of radiation. How damaging is the radiation for organic molecules, for possible life forms that could exist there, or for life forms being transported to Mars? And because I’m with the Institute of Air and Space Medicine, I extend that to see how habitable Mars could be for human beings.
AM: What sort of answer have you found to that last question? Many people think the radiation environment of Mars is one of the main barriers to humans living on the planet.
GD:Actually, the radiation environment of Mars is less serious than the radiation of the moon, because Mars has an atmosphere. On Earth, the magnetic field and the atmosphere keep the cosmic radiation away. Our atmosphere has a shielding of about 1,000 grams per square centimeters, so there’s very little radiation arriving on the Earth’s surface.
On Mars, there’s no magnetic field but there is an atmosphere. Because the atmospheric pressure is less than six millibars, the shielding is 60 grams per square meter. That’s nearly a factor of a 100 less than Earth’s, so the annual radiation dose on Mars is about 100 times more than the annual radiation dose on Earth. But there are also areas on Earth, such as in Brazil, where the natural radiation dose also is about a factor of 100 higher than usual.
Of course, the composition of the radiation is different on Mars. For instance, on Earth we have the back-scattering neutrons. But the only thing I think is a problem for people on Mars is the so-called solar flares, which are also called solar particle events. These are eruptions of the sun that blast out a high dose of radiation. To guard against these on Mars, we’ll have to build shelters.
So on Mars, we will have to be careful about radiation, but there are other perimeters that I think are even more serious. One is the dust. We don’t know how hazardous the dust is. We know from the Viking experiments that if you add water to the soil, you get a burst of different gases. These gases include peroxides, and that can create difficulties for astronauts if they get that in their lungs.
|Viking Lander-1 (1976) showed dramatic changes during dust storm activity. The appearance of the sky changes with the atmospheric dust content. The false colors shown here show relative changes in atmospheric opacity over many sols. Credit: JPL/NASA|
The dust on Mars is composed of very tiny, one-micron-sized grains -– the same size of the dust grains on the moon. The lunar astronauts said that you can not get rid of the dust; it gets into everything. So I think it’s urgently required, before we send humans to Mars, for us to do a study with robots to see what happens if you gradually moisten the martian soil. I had proposed such an experiment for ExoMars, a rover of the European Space Agency, but they said it was too complicated.
AM:What is the projected timeline for ExoMars to get to Mars?
GD: There are two different plans. There is an ExoMars “light,” which would be scheduled to fly in 2011. Or the real ExoMars, with an orbiter, that would fly 2013.
For ExoMars I belonged to an international team that proposed a whole series of experiments. What survived from our proposal was a UV dosimeter, a radiation dosimeter, and an atmospheric package. That’s ok. Hopefully with a lifetime of about seven years, we can follow the radiation on Mars and keep track of solar flares.
AM:What sorts of changes do organisms experience from radiation? And how do those changes affect their evolution?
GD: The organisms that are exposed outside the space station are in a dormant state, so they cannot evolve. They are just surviving. We have found that solar ultraviolet radiation is the most damaging perimeter — it kills all organisms so far known. Except that Rosa de la Torre from Spain recently exposed lichens, and discovered that they had the same biological activity as before they were exposed to the full sunlight. So that is something new. But we did find that if we shielded microorganisms against solar UV radiation with dust, even a dust sphere of just one centimeter, they survive pretty well in space. So that means little meteorites just one centimeter in diameter could travel for at least two weeks in space and the organisms inside would survive. I also participated in the NASA LDEF mission, the Long Duration Exposure Facility. Their microorganisms stayed in space for six years, and they also survived pretty well when they were shaded against UV radiation.
AM:You don’t notice any mutational changes that could result in virulent strains?
GD: Noooo! (laughs) The conditions of outer space are mutagenic, but the mutations are no different from what you’d find on Earth. And the radiation environment in space is not high enough to really get a lot of mutations.
|Bacillus subtilis survived six years in the vacuum and cold of space.
In our studies on the biological effects of radiation, we found that cosmic radiation is not homogeneously distributed. You have a heavy ion here and here and here, and every place that a heavy ion went through had a high degree of localized damage. In our experiments, we tracked the paths of these heavy ions. We had something called a BioStack – a stack of nuclear track detectors – and in-between there were things like seeds, animal eggs, and bacterial spores. After the space flight, we separated these pieces, took samples around the path of each ion, and analyzed them. Otherwise the radiation effects don’t do very much, because the dose is not high enough.
AM: So you’re not expecting, on a return trip from Mars, for bacteria to have mutated into a dangerous green slime of any sort.
GD:(laughs) Evolution took millions and billions of years. Nevertheless, I am a member of the ESA Planetary Protection Working Group, and back-contamination is a problem we have to take very seriously. It’s a concern of the public, even if it’s not so risky scientifically. There are a lot of things we must do to protect the Earth before these materials could be released.
But as I understand it, a sample return mission is not in the direct planning of NASA anymore, and Europe will not be able to do it by itself. I personally think we should develop the in situ instruments to do most of the studies on Mars, and not bring the samples back home. We have a lot of sophisticated, miniaturized instruments now that we can use.