Mars, in astronomy, 4th planet from the sun, with an orbit next in order beyond that of the earth.

Physical Characteristics

Mars has a striking red appearance, and in its most favorable position for viewing, when it is opposite the sun, it is twice as bright as Sirius, the brightest star. Mars has a diameter of 4,200 mi (6,800 km), just over half the diameter of the earth, and its mass is only 11% of the earth's mass. The planet has a very thin atmosphere consisting mainly of carbon dioxide (95%) with some nitrogen, argon, oxygen, and other gases. Mars has an extreme day-to-night temperature range, resulting from its thin atmosphere, from about 80°F; (27°C;) at noon to about -100°F; (-73°C;) at midnight; however, the high daytime temperatures are confined to less than 3 ft (1 m) above the surface.

Surface Features

A network of linelike markings first studied in detail (1877) by G. V. Schiaparelli was referred to by him as canali, the Italian word meaning "channels" or "grooves." Percival Lowell, then a leading authority on Mars, created a long-lasting controversy by accepting these "canals" to be the work of intelligent beings. Under the best viewing conditions, however, these features are seen to be smaller, unconnected features. The greater part of the surface area of Mars appears to be a vast desert, dull red or orange in color. This color may be due to various oxides in the surface composition, particularly those of iron. About one fourth to one third of the surface is composed of darker areas whose nature is still uncertain. Shortly after its perihelion Mars has planetwide dust storms that can obscure all its surface details.

Photographs sent back by the Mariner 4 space probe show the surface of Mars to be pitted with a number of large craters, much like the surface of our moon. In 1971 the Mariner 9 space probe discovered a huge canyon, Valles Marineris. Completely dwarfing the Grand Canyon in Arizona, this canyon stretches for 2,500 mi (4,000 km) and at some places is 125 mi (200 km) across and 2 mi (3 km) deep. Mars also has numerous enormous volcanoes—including Olympus Mons (c.370 mi/600 km in diameter and 16 mi/26 km tall), the largest in the solar system—and lava plains. In 1976 the Viking spacecraft landed on Mars and studied sites at Chryse and Utopia. They recorded a desert environment with a reddish surface and a reddish atmosphere. These experiments analyzed soil samples for evidence of microorganisms or other forms of life; none was found. In 1997, Mars Pathfinder landed on Mars and sent a small rover, Sojourner, to take soil samples and pictures. Among the data returned were more than 16,000 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and extensive data on winds and other weather factors. Mars Global Surveyor, which also reached Mars in 1997 and remained operational until 2006, returned images produced by its systematic mapping of the surface. The European Space Agency's Mars Express space probe went into orbit around Mars in late 2003 and sent the Beagle 2 lander to the surface, but contact was not established with the lander. The American rovers Spirit and Opportunity landed successfully in early 2004 and have explored the Martian landscape (Spirit became immobilized in 2008). In 2008 NASA's Phoenix lander touched down in the planet's north polar region; it conducted studies for five months.

Analysis of the satellite data indicates that Mars appears to lack active plate tectonics at present; there is no evidence of recent lateral motion of the surface. With no plate motion, hot spots under the crust stay in a fixed position relative to the surface; this, along with the lower surface gravity, may be the explanation for the giant volcanoes. However, there is no evidence of current volcanic activity.

There is evidence of erosion caused by floods and small river systems as well as evidence of ancient lakebeds. The possible identification of rounded pebbles and cobbles on the ground, and sockets and pebbles in some rocks, suggests conglomerates that formed in running water during a warmer past some 2-4 billion years ago, when liquid water was stable and there was water on the surface, possibly even large lakes or oceans. Rovers have identified minerals that only form in the presence of liquid water. There is also evidence of flooding that occurred less than several million years ago, most likely as the result of the release of water from aquifers deep underground or the melting of ice. However, other evidence suggests that the water would have been extremely salty and acidic. Data received beginning in 2002 from the Mars Odyssey space probe suggests that there is water in sand dunes found in the northern hemisphere, and the Mars Reconnaissance Orbiter, which went into orbit around the planet in 2006, collected radar data that indicates the presence of large subsurface ice deposits in the mid-northern latitudes of Mars. Most of the known water on Mars, however, lies in a frozen layer under the planet's large polar ice caps, which themselves consist of water ice and dry ice (frozen carbon dioxide); the lander Phoenix found and observed frozen water beneath the soil surface in the north polar region in 2008.

Seasonal Changes

Because the axis of rotation is tilted about 25° to the plane of revolution, Mars experiences seasons somewhat similar to those of the earth. One of the most apparent seasonal changes is the growing or shrinking of white areas near the poles known as polar caps. These polar caps, which are are composed of water ice and dry ice (frozen carbon dioxide). During the Martian summer the polar cap in that hemisphere shrinks and the dark regions grow darker; in winter the polar cap grows again and the dark regions become paler. The seasonal portion of the ice cap is dry ice. When the ice cap is seasonally warmed, geyserlike jets of carbon dioxide gas mixed with dust and sand erupt from the ice.

Astronomical Characteristics

The mean distance of Mars from the sun is about 141 million mi (228 million km); its period of revolution is about 687 days, almost twice that of the earth. At those times when the sun, earth, and Mars are aligned (i.e., in opposition) and Mars is at its closest point to the sun (perihelion), its distance from the earth is about 35 million mi (56 million km); this occurs every 15 to 17 years. At oppositions when Mars is at its greatest distance from the sun (aphelion) it is about 63 million mi (101 million km) from the earth. It rotates on its axis with a period of about 24 hr 37 min, a little more than one earth day.

Satellites of Mars

Mars has two natural satellites, discovered by Asaph Hall in 1877. The innermost of these, Phobos, is about 7 mi (11 km) in diameter and orbits the planet with a period far less than Mars's period of rotation (7 hr 39 min), causing it to rise in the west and set in the east. The outer satellite, Deimos, is about 4 mi (6 km) in diameter.


See J. K. Beatty and A. Chaikin, ed., The New Solar System (3d ed. 1991).

Mars, in Roman religion and mythology, god of war. In early Roman times he was a god of agriculture, but in later religion (when he was identified with the Greek Ares) he was primarily associated with war. Mars was the father of Romulus, the founder of the Roman nation, and, next to Jupiter, he enjoyed the highest position in Roman religion. The Salii, his priests, honored him by dancing in full armor in the Campus Martius, the site of his altar. Chariot races and the sacrifice of animals were primary features of the festivals held in his honor in March (named for him) and October. Mars was represented as an armed warrior. His attributes include the spear and shield, and the wolf and woodpecker were sacred to him. He was frequently associated with Bellona, the Roman goddess of war.
'' Mars is a borough in Butler County, Pennsylvania, USA. The population was 1,746 at the 2000 census.


Mars is located at (40.696594, -80.012205).

According to the United States Census Bureau, the borough has a total area of 0.4 square miles (1.2 km²), all of it land.


The borough of Mars, Pennsylvania was founded in 1873, and is situated about halfway between the cities of Pittsburgh and Butler. The small community is nestled in a small valley along Breakneck Creek with PA 228 located about a mile south of Mars, and the Mars-Evans City Road located to the north. It is home to the popular roadside attraction, the Mars "Spaceship" or "Flying Saucer". It is also home to the Mars Station which is one of the last railroad depots still standing from the now defunct Pittsburgh and Western Railroad.

In 1873, Samuel Parks constructed a home and a water-powered gristmill along Breakneck Creek. Parks then decided to have a post office placed in his home, so he received help from his friend, Samuel Marshall to help establish it. The name became Mars. No one is sure how the name "Mars" came into being. Some say it was Park's wife who enjoyed astronomy, or it was shortened after Samuel Marshall's name. In 1877, the Pittsburgh, New Castle and Lake Erie Railroad created a stop in the area, and named it Overbrook. Since the name of the railroad's stop conflicted with the borough's name, the railroad had it changed so it would match the borough's. Plus, there was already a community in Pennsylvania with the name, "Overbrook". On March 6, 1895, Mars was incorporated as a borough.

In 1904, the Pittsburgh and Butler Railway gained permission from Mars to construct its right-of-way through the borough. The line would eventually become part of the Pittsburgh, Harmony, Butler and New Castle Railway. The line closed in 1931. The USS Mars (AFS-1) was named after the borough. The ship became part of the United States Pacific Fleet in 1963, and was decommissioned in 1998. It was then sunk in 2006 as a target vessel. The bell of the USS Mars was donated to the borough, and has become a permanent memorial in the downtown park.

The 1996 comedy film, Kingpin, was filmed throughout the borough. There was also a Kraft salad dressing commercial that was filmed in downtown in 2000. However, the commercial never aired on television. In 2006, Mars was featured briefly on The History Channel.

Canadian musician John Southworth named his first album Mars, Pennsylvania for the town, which he had passed through many years earlier on a school trip.

Residents of Mars are often called "Martians", or "Planets" because of the high school team name.


The Mars Area School District serves the boroughs of Mars, and Valencia. It also serves Adams Township and Middlesex Township in Butler County. The Mars Fightin' Planets are one of the many teams located in the north Pittsburgh area.


As of the census of 2000, there were 1,746 people, 687 households, and 395 families residing in the borough. The population density was 3,906.5 people per square mile (1,498.1/km²). There were 715 housing units at an average density of 1,599.7/sq mi (613.5/km²). The racial makeup of the borough was 98.68% White, 0.46% African American, 0.06% Native American, 0.40% Asian, 0.06% Pacific Islander, 0.11% from other races, and 0.23% from two or more races. Hispanic or Latino of any race were 0.40% of the population.

There were 687 households out of which 25.0% had children under the age of 18 living with them, 45.7% were married couples living together, 10.8% had a female householder with no husband present, and 42.4% were non-families. 38.3% of all households were made up of individuals and 24.3% had someone living alone who was 65 years of age or older. The average household size was 2.16 and the average family size was 2.89.

In the borough the population was spread out with 18.6% under the age of 18, 5.7% from 18 to 24, 24.8% from 25 to 44, 17.8% from 45 to 64, and 33.2% who were 65 years of age or older. The median age was 46 years. For every 100 females there were 70.0 males. For every 100 females age 18 and over, there were 64.2 males.

The median income for a household in the borough was $33,073, and the median income for a family was $46,136. Males had a median income of $34,083 versus $26,080 for females. The per capita income for the borough was $17,701. About 7.8% of families and 9.3% of the population were below the poverty line, including 11.8% of those under age 18 and 14.4% of those age 65 or over.


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