Mercury is extremely difficult to observe from Earth because of its small size and proximity to the Sun. Its surface is similar to the surface of the moon and is full of craters sustained billion of years ago from impacting comets and asteroids. The craters range in size from small bowl-shaped craters to craters hundreds of miles wide. One of the largest craters is referred to as the Caloris Basin, which stretches over 900 miles in diameter. Despite the craters, Mercury's surface is more uniform than the surface of the Earth, though it does have some ridges, high escarpments, and valleys among its smooth plains. Mercury also features unusual formations called tidal bulges. A tidal bulge is a kind of gravitational tide and happens because the gravitational force of one object on another is not uniform across its diameter. In the case of Mercury, its surface is warped in places where the sun's gravitational pull is strongest. The sun's gravitational force on Mercury is 17 times that of the moon's on Earth.
How big is this planet?
Mercury is the smallest planet. Its surface area only occupies about 15 percent of the Earth's surface area. It's only a little more than five percent as massive as Earth and only has 5.5 percent of Earth's volume.
How long does it take to orbit the sun?
What is its gravity like?
Mercury's gravity is 38% the gravity of Earth. A 100 pound Earthling would weigh 38 pounds on Mercury.
How far is it from the sun? From the Earth?
Mercury is the closest planet to the sun. At its closest, it is 28,600,000 miles from the sun. At its farthest, it is 43.4 million miles away. When Mercury and Earth are on the same side of the sun, the two planets may come within 57,000,000 miles of each other. When they are on opposite sides of the sun, they may be as far as 129,000,000 miles apart.
What is its atmosphere like?
Mercury has an extremely thin atmosphere that consists of atoms being swept off its surface by solar wind.
What's the temperature like?
Mercury is a planet of extremes. The side facing the sun may reach temperatures of 950 degrees F and the side facing away from the sun may drop to -346 degrees F.
How many moons does it have?
Mercury's orbit is highly eccentric. This means its orbit is not as circular as other planets.