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Elements that have been detected include sodium and potassium , produced by sputtering ( also found in the atmospheres of Mercury and Io ) ; helium-4 and neon from the solar wind ; and argon-40 , radon-222 , and polonium-210 , outgassed after their creation by radioactive decay within the crust and mantle .
 astronomical object: Mercury; astronomical object: Io
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 astronomical object: Mercury; astronomical object: Io