10 Cool Facts about the Planet Mercury
The Planet Mercury - First Rock from the Sun
The planet Mercury is as fascinating as it is mysterious. Prior to NASA's MESSENGER spacecraft arriving in orbit around the tiny planet, very little was known about Mercury. The Romans named the planet after the fleet-footed messenger god Mercury due to the speed at which it moves across our sky. However, the first known recorded observations of the planet were most likely made by Assyrian astronomers in the 14th century BC, who referred to Mercury as "the jumping planet." Let's take a look at 10 cool facts about the planet Mercury...
[Image: Composite image of Mercury taken by MESSENGER Wide Angle and Narrow Angle Cameras. (Credit: NASA/Johns Hopkins University APL/Carnegie Institution of Washington)]
Mercury Fact #1 - Eccentric Orbit
Mercury, the closest planet to the sun, has a very elliptical orbit. In fact, it has the most eccentric orbit of all the planets. Its orbit takes the planet as close as 29 million miles to the sun and as far away as 43 million miles. If one was to stand on the surface of Mercury at its closest point to the sun, the sun would appear almost three times as large in the sky as it does on earth.
Mercury Fact #2 - Temperatures
The daytime surface temperatures on Mercury can reach 800 degrees Fahrenheit. However, because the planet has no atmosphere to trap that heat in, the nighttime surface temperatures can plunge to -280 degrees Fahrenheit as that heat radiates out into space.
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Mercury Fact #3 - Length of Year
Mercury orbits the sun at around 107,372 miles an hour -- nearly 31 miles per second faster than any other planet. Due to its orbital speed and closeness to the Sun, Mercury completes each solar orbit in 88 days -- as compared to an Earth year of roughly 365 days.
More About the Planet Mercury - Science Channel Space School: Planet Mercury
Mercury Fact #4 - The Caloris Basin
One of the largest landmarks on the surface of Mercury is the Caloris Basin. This impact crater is approximately 800 miles in diameter and was caused by an asteroid impact during the early years of the solar system. It is estimated that the asteroid was roughly 60 miles wide and the impact released an amount of energy equal to a trillion 1-megaton bombs (NASA Solar System Exploration: About Mercury). The impact was so massive scientists believe it reshaped the topography on the other side of the planet. The Caloris Basin is one of the largest known impact craters in our entire solar system. In fact, the entire state of Texas could fit within the crater.
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Mercury Fact #5 - Rotation & Length of Day
Although astronomers originally believed that the same side of Mercury always faced the sun (meaning its "day" was equal to its "year"), they discovered in 1965 through the use of Doppler radar that the planet actually completes three rotations (also known as sidereal rotations) for every two orbits around the sun. This correlates to a sidereal day that is equal to 58.65 Earth days. However, the planet's solar day (between two meridian transits of the sun) is around 176 Earth days.
More About the Planet Mercury - The Galaxy Channel: The Inner Planet Mercury
Mercury Fact #6 - Atmosphere
Mercury has no atmosphere. Rather, it has a thin exosphere. This exosphere is comprised of atomic sized particles forced from its surface by solar winds and meteoritic collisions. Because of this condition, there is no wind on the surface of the planet (and, thus, no weathering) and no atmospheric friction to slow-down or burn-up meteorites as they fall to the surface.
Mercury Fact #7 - Size
Mercury, one of the four terrestrial planets in our solar system, is the smallest planet in the solar system. Now, you may be wondering about Pluto, which is smaller. However, Pluto is no longer considered a planet by the scientific community; rather, it is now a member of a new class of space objects called dwarf planets. In fact, it is smaller than the largest satellites in our solar system -- Jupiter's moon Ganymede and Saturn's moon Titan. The planet has a diameter of 3,032 miles, which is far closer to that of the moon's 2,159-mile diameter than the earth's 7,926-mile diameter. In terms of volume, the earth is nearly 18 times larger than Mercury.
More About the Planet Mercury - National Geographic - Journey to the Planets (Venus and Mercury)
Mercury Fact #8 - Density
Mercury is the second densest planet (5.43 g/cubic centimeter). Only our own earth is denser (5.52 g/cubic centimeter). However, if you factor out gravitational compression, Mercury would be the densest planet. Mercury's high density is the result of a large iron core that measures about 75 percent of the planet's radius (or roughly 42 percent of its volume) -- much larger than earth's iron core (17 percent of its volume). This density results in a surface gravity that is roughly equal to that of Mars, despite the fact that Mercury is considerably smaller.
Mercury Fact #9 - Magnetic Field
Mercury has a magnetic field that is comparable in nature to that of the earth's (i.e., global and dipolar). However, its strength is believed to be only around 1.1 percent of earth's magnetic field.
Mercury Fact #10 - Gravity
Gravity on the surface of Mercury is only 38 percent of that on earth. This means that if you weigh 150 pounds on earth, you would weigh only 57 pounds on Mercury.
Links to More Great Mercury Resources
- National Geographic
- NASA History Office
Atlas of Mercury
- Planetary Science Research Discoveries, University of Hawaii
- NASA Solar System Exploration
- NASA Lunar and Planetary Science
- NASA MESSENGER
Mission to Mercury website
- NASA Marshall Space Flight Center
Discovery Program: MESSENGER
- NASA JPL & California Institute of Technology
NASA Antenna Cuts Mercury to Core, Solves 30 Year Mystery
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