Question 4: the correct answer is Mercury. Got it right? Award yourself 1 point.
Question 5 of 10
In what year did human beings first set foot on the Moon?
Why, in question 4: What is the planet closest to the Sun?
The answer is Mercury. It lies, on average, about 58 million kilometers from the Sun, less than 40% of Earth's distance. It is also the smallest planet in the Solar System.
Hot by day, cold by night
Even so close to the Sun, Mercury is not the hottest planet. With no atmosphere to hold heat, the sunlit side goes above 400 °C, while the dark side drops below −170 °C.
It orbits the Sun in just 88 Earth days, the shortest year in the Solar System, yet it rotates slowly: the interval between two sunrises there lasts about 176 Earth days.
Its surface is full of craters, similar to the Moon's, because there is no wind or water to erase the marks of impacts.
Even so close to the Sun, Mercury has ice, inside craters near the poles where sunlight never reaches. NASA's Messenger probe confirmed this in 2012.
