Mars appears to have cooled with time, so radiation may be the problem instead.

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The downside of unnecessary CTs is extra radiation, a particular problem in kids and young adults.

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One way to address this problem is to harvest radiation from multiple sources.

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Radiation, too, should not be a problem if a newly launched meteorite is at least the size of a soccer ball.

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"That led to the idea that one could give most or all of the radiation closer to the original tumor bed and that would solve the problem, " says George Sledge, a past president of the American Society of Clinical Oncology and co-director of the breast-cancer program at Indiana University Simon Cancer Center, in Indianapolis.

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The problem, he notes, is that public fears about cell phone radiation do not appear to be supported by the preponderance of scientific research.

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Studies at the Gale Crater landing site have been on hold since the beginning of March after engineers discovered a problem with Curiosity's computer memory, possibly caused by space radiation.

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