Mercury

Introduction

The smallest planet in our solar system and the nearest to the Sun, Mercury is just slightly larger than Earth's Moon. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system! That title belongs to nearby Venus, thanks to its thick atmosphere. But Mercury is the fastest planet, bolting around the Sun every 88 Earth days. Mercury was probably named for the swiftest of the ancient Roman gods.

Size and Distance

With the radius of 1,516 miles (or 2,440 kilometers), Mercury is a little more than 1/3 the width of Earth. If Earth were the size of a nickel, Mercury would be about as big as a blueberry.

From an average distance of 36 million miles (58 million kilometers), Mercury is 0.4 astronomical units (AU) away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 3.2 minutes to travel from the Sun to Mercury.

3D Model:

Orbit and Rotation

Mercury's highly eccentric, egg-shaped orbit takes the planet as close as 29 million miles (or 47 million kilometers) and as far as 43 million miles (70 million kilometers) from the Sun. It speeds around the Sun every 88 days, traveling through space at nearly 29 miles (47 kilometers) per second, faster than any other planet.

Mercury spins slowly on its axis and completes one rotation every 59 Earth days. But when Mercury is moving fastest in its elliptical orbit around the Sun (and is closest to the Sun), each rotation is not accompanied by a sunrise and sunset like it is on most other planets. The morning Sun appears to rise briefly, set and rise again from some parts of the planet's surface. The same thing happens in reverse at sunset for other parts of the surface. One Mercury solar day (one full day-night cycle) equals 176 Earth days—just over two years on Mercury.

Mercury's axis of rotation is tilted just about 2 degrees with respect to the plane of its orbit around the Sun. This means that it spins nearly perfectly upright and so does not experience seasons like many other planets do.

Structure

Mercury is the second densest planet, after Earth. It has a large metallic core with the radius of about 1,289 miles (pr about 2,074 kilometers), about 85% of the planet's radius. There is evidence that it is partly molten, or liquid. Mercury's outer shell, comparable to Earth's outer shell (called the mantle and crust), is only about 400 kilometers (or 250 miles) thick.

Formation

Mercury formed about 4.5 billion years ago when gravity pulled swirling gas and dust together to form this small planet nearest to the Sun. Like its fellow terrestrial planets, Mercury has a central core, a rocky mantle and a solid crust.