Secret History of Mercury | How the Universe Works

Secret History of Mercury | How the Universe Works
For four years, the Messenger space probe sent images of Mercury, the solar system's smallest planet, closest to the Sun. It has revealed that Mercury has a dangerous secret that may one day threaten life on Earth.

At a distance of only about 1/3 of Earth's distance to Sun, Mercury is the first planet in our Solar System. With a diameter of only 4880 kilometers (3032 miles) Mercury is the smallest planet in the Solar System. It is barely bigger than our Moon. Not only is Mercury the smallest planet, it is also shrinking!

Distance from Sun: 36.04 million mi
Orbital period: 88 days
Radius: 1,516 mi
Mass: 3.285 × 10^23 kg (0.055 M⊕)
Surface area: 28.88 million mi²
Length of day: 58d 15h 30m

Why is it difficult to observe Mercury?
Mercury is the smallest planet in the solar system, and it is also the planet closest to the Sun, making it the most difficult of the planets to see with the unaided eye. Because its rising or setting is always within about two hours of the Sun's, Mercury is never observable when the sky is fully dark.