Mercury is the littlest planet in the Solar System and the closest planet to the Sun. With a size of just over 3,000 miles, this little planet is no more than 1/3 how big is Earth and no more than 40% bigger than Earth’s moon. On a level where Earth is how big is a baseball, Mercury could be about how big is a tennis ball.
Mercury features a very elongated orbit that takes the planet about 28.5 million miles from the Sun at its closest approach, referred to as PERIHELION, and as far as 43 million miles at its farthest, referred to as paykwik. At perihelion, the Sun would seem nearly 3 x larger and about eleven times brighter when viewed from the top of Mercury than what we see from the top of Earth (but the sky on Mercury could be black because Mercury does not have any air). Mercury is really close to the Sun that it’s usually obscured because of it, making Mercury difficult to examine from the Earth even although the little planet is no more than 48 to 50 million miles from the Earth at its closest approach.
Traveling at a rate of approximately 108,000 miles per hour, Mercury completes one orbit across the Sun in about 88 Earth-days. The Earth travels about 66,000 miles per hour, and completes one orbit across the Sun every 365 days. Mercury completes more than four orbits of the Sun in one Earth-year. On the other hand to this short year, days and nights on Mercury are extremely long. Mercury turns slowly on its axis, taking about 59 Earth-days to perform just one rotation. Mercury only completes three rotations on its axis over the span of two orbits across the Sun. This means that three days on Mercury last two Mercurian-years.
Mercury was the name of the Roman messenger god who carried messages and performed errands for other gods. Mercury was also the god responsible for watching over trade, commerce, travelers and merchants. Mercury was often associated with peace and prosperity, and was also considered a god of the winds due to his speed. Because Mercury orbits the Sun faster than any other planet in the Solar System, ancient civilizations, including Mayans, Egyptians, Greeks and Romans, envisioned this speeding “star” as a messenger god inside their religions and myths.
Mercury’s surface temperatures vary dramatically, from over 800 degrees Fahrenheit quietly facing the Sun to about minus 300 degrees Fahrenheit quietly facing away. This range in surface temperature between Mercury’s sunlit-side and dark-side is the absolute most extreme for almost any planet in the Solar System. Mercury simultaneously broils and freezes… literally! A major contributor to this cycle of extreme heat and cold is the fact Mercury is too small to retain a significant atmosphere. Mercury comes with an atmosphere, but it’s so thin – no more than 1-trillionth the density of Earth’s atmosphere – that it’s practically non-existent. This thin atmosphere prevents Mercury from retaining and circulating heat across the planet. In order the small planet rotates, the side no longer exposed to the Sun cools dramatically while the side facing the Sun roasts.
Mercury’s thin atmosphere contains traces of elements from the solar wind and gases which were baked from the planet’s crust and surface rocks. A planet retains its atmosphere with its gravitational pull. Mercury does not need sufficient mass to retain – by gravitational pull – an amazing atmosphere. Mercury’s surface gravity is no more than 1/3 of the Earth’s. This means that a person who weighs 100 pounds on Earth would only weigh about 38 pounds on Mercury. Also, a planet as close to the Sun as Mercury is even less likely to retain a thick atmosphere than a more distant planet like Earth because it’s constantly being blasted by solar radiation. Charged particles emitted by the Sun are scorching the planet, and this atomic debris does manage to amass, but the intense heat combined with Mercury’s weak gravity allows the gases to escape.
Mercury is composed of about 70% iron and about 30% silicate material. It’s believed that a lot of of Mercury’s iron is concentrated in its core. This core, the densest of some of the planets in the Solar System, accounts for around 75% of Mercury’s volume. This means that Mercury’s core is proportionally bigger than any other planet in the Solar System. This core may be responsible for creating Mercury’s weak – significantly less than 1% as strong as Earth’s – but still detectable magnetic field. This magnetic field is a sign that Mercury’s core contains molten iron and isn’t completely solid. The fluid interior could – like Earth’s core – behave like a molten conductor. As Mercury spins on its axis, the molten iron in the core could generate the magnetic field that surrounds the tiny planet.