Fill in the blanks.

Mercury is one of the …………………….. (less / little / least) explored planets in the solar system. Much of …………………….. (which / that /what) we know about Mercury comes from NASA’s Mariner 10 mission, which ………………………. (flow / flew / has flown) by the planet three times in 1974 and 1975. Mariner ……………………… (can / could) see only half of the planet. During its recent flyby, Messenger ……………………….. (was / can) able to observe about half of the remaining area. The new images……………………….. (showed / shown / show) that Mercury is different from the other rocky objects in our inner solar system—Venus, Earth, Mars, and the moon. Other observations ……………………….. (include / including / includes) tons of craters, huge cliffs, evidence of volcanoes, and a strange, spider-shaped formation.

Answers

Mercury is one of the least explored planets in the solar system. Much of what we know about Mercury comes from NASA’s Mariner 10 mission, which flew by the planet three times in 1974 and 1975. Mariner could see only half of the planet. During its recent flyby, Messenger was able to observe about half of the remaining area. The new images show that Mercury is different from the other rocky objects in our inner solar system—Venus, Earth, Mars, and the moon. Other observations include tons of craters, huge cliffs, evidence of volcanoes, and a strange, spider-shaped formation.