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Astrobiologist David Morrison has spoken of repeated disruption of his work by popular anti-scientific phenomena , having been called upon to assuage public fears of an impending cataclysm involving an unseen planetary object - first in 2008 , and again in 2012 and 2017 .
 David Morrison
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 David Morrison