The smallest of the planets in the Solar System, Mercury is an interesting place. Incredibly dense due to its proportionately large core Mercury is thought to have been once a much larger planet.
Mercury is the smallest planet — it is only slightly larger than Earth's moon. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters. About 4 billion years ago, an asteroid roughly 60 miles (100 kilometers) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Known as the Caloris Basin, this crater could hold the entire state of Texas. Another large impact may have helped create the planet’s odd spin.
- Mercury is the smallest planet in our solar system -- only slightly larger than the Earth's moon.
- It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.
- One day on Mercury (the time it takes for Mercury to rotate or spin
once) takes 59 Earth days. Mercury makes a complete orbit around the sun
(a year in Mercury time) in just 88 Earth days.
- Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like Earth's moon.
- Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micro-meteoroid impacts create Mercury's exosphere.
- Mercury has no moons.
- There are no rings around Mercury.
- Only two spacecraft have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.
- No evidence for life has been found on Mercury. Daytime temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius) and drop to -290 degrees Fahrenheit (-180 degrees Celsius) at night. It is unlikely life (as we know it) could survive on this planet.
- Standing on Mercury's surface at its closest point to the sun, the sun would appear more than three times larger than it does on Earth.