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There are two basic kinds of space radiation: radiation from the Sun and cosmicradiation streaming in from outside the solar system. In addition, storms on theSun can cause large flares that occasionally send out a flood of high levels ofradiation that greatly increases the danger to astronauts, especially thosetravelling beyond Earth orbit.Space scientists are trying to devise ways to shield spacecraft against thisradiation, but the task is complicated by the fact that there are still manyunknowns about the exact nature and intensity of space radiation and particularlyabout its biological effects on various organisms, including humans. Canadianresearchers have been very active in studying this problem and have developeddosimeters worn by astronauts to monitor their exposure.Baillie describes C. elegans as a “biological accumulating dosimeter” that willprovide important clues about the effects of long-term radiation exposure. Oneissue he is interested in is how organisms respond to the changing radiationenvironment in space—the varying doses of different kinds of radiation that occurover time.“Nothing is known about longer-term exposure to the different types of radiationin space,” he commented in a paper describing his project. “The wide range ofradiation sources needed to mimic the space environment are not available onthe ground; therefore it is imperative that we develop [an] accumulatingdosimeter for use in space.”He also plans to compare how the natural DNA repair mechanisms that exist inall living things work in space versus how they function on earth.One intriguing possibility is that a brief exposure to low levels of space radiationmight provide organisms with the ability to withstand more damaging effects fromlong-term exposure or pulses of high levels of radiation, such those caused bysolar flares. A period of low-level exposure might “turn up” the natural DNA repairsystem so that it’s better able to cope with higher radiation levels. “We’rebeginning to think there may be some evidence for that,” said Baillie. “We have tolook more carefully at our data but it may well be the case.”If this type of DNA repair turns out to be possible in higher organisms, includinghumans, it would make long-duration spaceflight a much safer and cheaperproposition. Baillie noted that the amount of shielding required to protectastronauts from space radiation is “really enormous” and would significantlyincrease the cost of space missions.38
But an extraordinary amount of shielding might not be needed if a week or two ofexposure to the normal background radiation in space equips astronauts’ DNA tofight off damage from longer or more intense exposures. “We may luck out thatlow exposure may pre-adapt the system for higher levels of repair,” Baillie said.ELERAD was led by Principal Investigator David Baillie of Simon Fraser University, supported bya science team of CO-Is, with project management at the Canadian Space Agency.Planetary Exploration and Space AstronomyAPXS on Mars Science LaboratorySending a robotic vehicle to hunt for rocks on Mars is a high-stakes proposition.Assuming it survives the considerable perils of a long journey from Earth and arisky landing on the surface of Mars, a rover—and the scientists who control itfrom Earth—still face enormous challenges seeking out the best areas to studyand collecting rock and soil samples most likely to reveal the secrets of Mars’history and evolution.A Canadian-built instrument will play a key role in making this difficult task easieron the Mars Science Laboratory (MSL), a NASA mission scheduled to belaunched in 2009 and to land on Mars in 2010. Called APXS (Alpha Particle X-ray Spectrometer), the instrument can quickly determine the elements containedin rock and soil samples before they are sent for more detailed analysis inanother instrument on board the rover.Located on the robotic arm used to dig up the samples, APXS is a pop-can-sizedinstrument that can be maneuvered into contact with a sample, then bombard itwith alpha particles and x-rays. The elements in the sample respond by emittingx-rays in characteristic ways that enable APXS to identify them and measuretheir abundance.APXS is a highly precise instrument that can identify the percentages ofelements like sulphur, iron, silicon and magnesium in a sample, and can evendetect tiny amounts of trace elements like nickel, chlorine and zinc. “We can readout from the elemental composition what the history of this rock or soil is and howit was formed,” said Ralf Gellert, a physics professor at the University of Guelph,who heads the APXS project.For example, some elements, such as iron, silicon or magnesium suggest a rockis volcanic in origin, while those containing more salts, such as sulphur, chlorineor bromine, are likely to have once come in contact with water. Finding evidence39
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