Greg Bennett, age 12, of Indianapolis, Indiana, for his question:
When were the moons of Mars discovered?
The Martian moons are too small to be seen without the help of a powerful telescope. Astronomers have been using telescopes to observe details on the planet Mars since the 1600's and you would think that the tiny moons would have been spotted centuries ago. However, there are reasons why nobody noticed them until the late 1800's.
There are times when Mars is way out of sight and times when it seems no higher than a glowing red lamp on top of the nearest mountain. Astronomers say that there are favorable and unfavorable times for viewing the details of the red planet, and the favorable times are very rare. They occur at a period of opposition when the earth is between Mars and the sun. This event occurs once in a period of two years and 50 days. Then Mars is in opposition but not every opposition is favorable. In fact, a favorable opposition occurs only once in 15 or 17 years.
The last favorable opposition was in 1956 and the next will come in 1971. At these times, the earth and Mars are separated by only 35 million miles and the glowing red. planet appears bright above us in the night skies for several weeks. Then is the time for amateurs with small telescopes and experts with big telescopes to observe all they can.
The Martian moons were discovered during a favorable opposition in the year 1877. They were spotted by the American astronomer Asaph Hall with the help of a large telescope at Washington's Naval Observatory. The two little moons appeared as tiny dots of light, very close to their parent planet. It was decided to name them Phobos and Deimos Fear and Panic for the two unworthy companions of Mars, the ancient god of war.
Phobos is estimated to be about ten miles wide and it orbits around Mars about 3,700 miles above the planet's surface. Deimos circles around about 12,500 miles above the planet and it is somewhat smaller than Phobos. Phobos completes three orbits while Mars rotates once around its axis. Seen from the surface of the planet, the tiny inner moon appears to rise in the west and set in the east. Deimos takes a little more than 30 hours to complete its orbit or a few hours longer than the Martian day. The outer moon takes two and a half days to journey over the Martian skies and between rising and setting it passes through all lunar phases twice.
Our spacecraft Mariner IV sent back some very vivid photos of Mars taken from 6,100 miles above the surface, but no new data was added on the Martian moons. Astron¬omers already had figured out the speeds and orbits, the locations and approximate sizes of the tiny satellites.
Estimates on the density of the Martian moons led to some rather astonishing science fiction type speculation. Our scientists figured that Phobos is made of materials lighter than any known solid. Russian scientists used this data to make a wild guess that Phobos must be hollow. And, they argued, a hollow satellite must be artificially made by intelligent beings. Nobody has proved this true or false. The fabulous notion of life on Mars mush wait until our spacemen land there and relay on¬ the spot information that can be accepted as facts.