Mercury: The Messenger Planet

Mercury is the planet closest to the sun and it is also the second smallest planet, behind pluto. It was named after the Roman God of Commerce and Thievery who bore wings on his boots and cap. It was probably named so because Mercury seemed to move swiftly across the sky. Since Mercury is closest to the sun, it does have the shortest year (time it takes to make one revolution around the sun). Another interesting fact is that although the side closest to the sun is extremely hot, the other half that faces away from the sun is always extremely cold.

Here is some general planetary data on Mercury

Detailed Information on Mercury:

Mercury's Phases--

Much like the Earth's moon, Mercury can be seen going through "changes" in size and shape that are called phases. This occurs from Mercury's sunlit side being visible from Earth at various times. For 116 days as Mercury and the Earth travel around the sun, almost all its sunlit area is visible from the Earth because Mercury is on the other side of the Sun. When Mercury moves toward the earth, less and less of this sunlit area can be seen. After 36 days, only half of its surface is visible. Soon, after about 22 days, it nears the same side of the sun that the earth is on and then only a thin sunlit area is visible. After Mercury passes in front of the sun and begins moving away from earth, then more of the sunlit are can be seen again.

When Mercury is on the same side of the sun as the earth, then its dark side faces us. Since Mercury and the earth orbit at different angles, Mercury is usually not visible at this point. However, every three to thirteen years the planet is in transit and can be seen as a black spot against the sun. This generally occurs in November and May, but mostly in November.

Surface and Atmosphere--

Also like our moon is Mercury's surface. It reflects about six percent of the light from the sun. Mercury's terrain consists of broad, flat plains, steep cliffs and craters similar to those on our moon. Its probable that the craters were formed by meteors and comets crashing into it when it was still a young planet. But even now, Mercury does not have enough of an atmosphere to slow down and burn up approaching meteors. Like the moon, Mercury is convered by a think layer of minerals called silicates in the form of timy particles.

While Mercury Mercury has a moonlike surface, its interior is more similar to that of the earth. Scientists generally believe that the interior consists of mainly iron and some other heavy elements. Since Mercury has a magnetic field around it, it is likely that it also has a large core of liquid iron, the same as the earth.

The sun's rays are approximately seven times as strong on Mercury as they are on earth whcih results in the planet being extremely dry, hot and virtually airless. It a person could stand on Mercury's surface, the sun would appear about two and a half times larger than it is viewed on earth. The temperature on the planet's surface may reach 801 degrees F. However, at night, that temperature may drop as low as -279 degrees F. Also, because of Mercury's lack of atmosphere, the sky is black and the stars can probably be seen during the day.

The reason that Mercury has such a weak atmosphere is that it is surrounded by an extremely small amount of helium, hydrogen, oxygen and sodium. This envelope of gases is so thin that the greatest possible atmospheric prassure (force exerted by weight of gases) is about 0.00000000003 lbs. per sq.in as compared to earths 14.7 lbs per sq.in. Scientists doubt that there is any life on Mercury because of the lack of oxygen and great heat.

Density and Mass--

Mercury's density is only slightly less than the earth's. However, since Mercury is much smaller than the earth, it has a lot less mass. Its smaller mass cuases its force of gravity to only be one third as strong as the earth's. Thus, an object that ways one hundred pounds on earths, would weigh only thirty-eight pounds on Mercury.

Flights to Mercury--

The first and only spacecraft to visit Mercury was the United States Mariner 10 . This unmanned spacecraft flew within 460 miles of Mercury on March 29, 1974. It passed by one more time on September 24, 1974 and photographed protions of Mercury's surface. It was the spacecraft that detected Mercury's magnetic field.

Mariner 10 was also the first spacecraft to study two planets. It made scientific measurements of Venus on its voyage to Mercury. Manned expiditions of Mercury will be difficult because of the unfavorable surface conditions, but time will tell.