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Mercury , the closest planet to the Sun at 0.4 AU , takes 88 days for an orbit , but the shortest known orbits for exoplanets take only a few hours , see Ultra-short period planet .
 Mercury
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:
 Mercury